Article: 217116 of rec.radio.amateur.antenna From: "Tom Donaly" Subject: Re: 73 Ohms, How do you get it? References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> Message-ID: Date: Tue, 13 Sep 2005 20:36:32 GMT Harry wrote: > Hi Tim and Reg, > > Thank you for your valuable information. Is there any website or > textbook that actually shows the step-by-step calculation of this magic > number which has been quoted so often in the cable industry? > > You know most video cables and connectors have characteristic > impedance, 75 Ohms. > > I am not afraid of math. I just like to understand the details of its > derivation. > > -- Harry > What you're seeking is in the book _Antenna Theory, Analysis and Design_ by Constantine A. Balanis, ISBN 0-471-59268-4. 73, Tom Donaly, KA6RUH Article: 217117 of rec.radio.amateur.antenna From: "KØHB" References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <6qudnRtjVJhVpLveRVn-tQ@comcast.com> <0ICdncTJkPKeVrveRVn-vA@comcast.com> Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Message-ID: Date: Tue, 13 Sep 2005 22:29:46 GMT "Dee Flint" wrote > > Nothing stops them from calling an immediate emergency meeting to address > temporarily suspending such limits in times of great need. > If a ham can only use their station "in times of great need" it's unlikely they'd have the equipment to put into service, so it's all a moot point. 73, de Hans, K0HB Article: 217118 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: 73 Ohms, How do you get it? Date: Tue, 13 Sep 2005 22:56:10 +0000 (UTC) Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> "Ham op" wrote > Transmission line calculations are much easier than antenna calculations. > ===================================== Antenna conductors ARE transmission lines and the same sort of calculations apply. ---- Reg. Article: 217119 of rec.radio.amateur.antenna Subject: Re: 73 Ohms, How do you get it? From: Cecil Moore Date: Tue, 13 Sep 2005 18:12:08 -0500 Message-ID: <1126653287_28145@spool6-east.superfeed.net> References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> Harry wrote: > I am a newbi in antennas. > > Here's my question: > > I know that a half-wave dipole in free space has > a feed-point impedance of approximately 73 ohms. > > Can anyone tell me **exactly** how this number is calculated. From "Antenna Theory" by Balanis: Rr = 2*Prad/|Io^2| = 73 ohms (4-93) Prad is found by integrating the Poynting Vector over a certain radius. Io is the current maximum magnitude. The ASCII limitation prevents much more than this. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Article: 217120 of rec.radio.amateur.antenna From: "KØHB" References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <6qudnRtjVJhVpLveRVn-tQ@comcast.com> <0ICdncTJkPKeVrveRVn-vA@comcast.com> Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Message-ID: Date: Tue, 13 Sep 2005 23:19:03 GMT "Dee Flint" wrote > > I was talking about temporarily taking in those left homeless and how it shows > a lack of humanitarianism. > O I C. I have no HOA restrictions, but if I did have some like that, then they'd just be friends visiting for a few weeks. 73, de Hans, K0HB Article: 217121 of rec.radio.amateur.antenna Subject: Re: Hot Flashes From: Cecil Moore Date: Tue, 13 Sep 2005 18:20:50 -0500 Message-ID: <1126653809_28153@spool6-east.superfeed.net> References: <43271ECF.10306@arrl.net> Henry wrote: A funny jpeg but this is an ASCII only newsgroup. It will probably be deleted by the usenet god. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Article: 217122 of rec.radio.amateur.antenna Subject: Re: 73 Ohms, How do you get it? From: Cecil Moore Date: Tue, 13 Sep 2005 18:23:43 -0500 Message-ID: <1126653984_28157@spool6-east.superfeed.net> References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> Harry wrote: > Thank you for your valuable information. Is there any website or > textbook that actually shows the step-by-step calculation of this magic > number which has been quoted so often in the cable industry? "Antenna Theory" by Balanis, second edition, Chapter 4. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Article: 217123 of rec.radio.amateur.antenna Subject: Re: 73 Ohms, How do you get it? From: Cecil Moore Date: Tue, 13 Sep 2005 18:43:42 -0500 Message-ID: <1126655181_28167@spool6-east.superfeed.net> References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> Reg Edwards wrote: > Antenna conductors ARE transmission lines and the same sort of > calculations apply. You're right, Reg. Without reflections from the ends of a dipole, the feedpoint impedance would be hundreds of ohms. A standing wave antenna is like a lossy transmission line where the loss is to radiation. And the SWR on a 1/2WL dipole standing wave antenna is quite high - in the neighborhood of 20:1. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Article: 217124 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: 73 Ohms, How do you get it? Date: Wed, 14 Sep 2005 00:41:57 +0000 (UTC) Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> It is equally correct to say that the radiation resistance of a dipole is 2*73 = 146 ohms, since this is the value when the radiation resistance is assumed to be uniformly distributed along its length as is the conductor resistance. For calculating purposes the radiation and conductor resistances can simply be added together. And when referred to the end of a dipole, at HF the radiation resistance is of the order of Q-squared * 73/2 = 3000 ohms. Although this is somewhat indeterminate because of the difficulty of feeding an isolated dipole at one end. The conductor diameter also plays a significant part. ---- Reg. Article: 217125 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: 73 Ohms, How do you get it? Date: Tue, 13 Sep 2005 17:47:09 -0700 Message-ID: <11iesohk2gnkf80@corp.supernews.com> References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> Just about any antenna textbook will show you the calculation of a half wavelength, infinitely thin dipole in free space. For that special case, the answer ends up being simply 30 * Cin(2 * pi), where Cin is a modification of the cosine integral Ci[*]. That's where the "magic number" comes from. Kraus' _Antennas_ is just one of the many textbooks which give the derivation for this. It takes about 3 pages and 23 equations for Kraus to derive. One assumption made in calculation of this value is that the current distribution is sinusoidal, an assumption that's true only for an infinitely thin antenna. For finite thickness wire, the calculation becomes much more difficult. The radiation resistance changes only slowly with wire diameter, however, so sinusoidal distribution is a reasonably good approximation provided that the antenna is thin. Feedpoint reactance, though, varies much more dramatically with both antenna length and diameter. Calculating its value exactly requires solution of a triple integral equation which can't be solved in closed form. That's why computer programs are used to solve it numerically. To include the effect of ground, you need to calculate the mutual impedance between the antenna and its "image". If the antenna is about 0.2 wavelength above ground or higher (for a half wave antenna -- the height must be greater if the antenna is longer), you can assume that the ground is perfect and get a pretty good result. Below that height, the calculation again becomes much more complicated because the quality of the ground becomes a factor. If you're interested in the numerical methods used, locate the NEC-2 manual (available on the web), which describes it. If you're satisfied with approximate results, the work by S.I. Shelkunoff provides formulas for free-space input impedance of antennas with finite diameter wire which can be solved with a programmable calculator or computer. They're detailed in "Theory of Antennas of Arbitrary Size and Shape", in Sept. 1941 Proceedings of the I.R.E. The formulas for R and X contain many terms involving sine and cosine integrals, which can be approximated with numerical series. You'll find additional information in his book _Advanced Antenna Theory_. For approximate calculations of mutual impedance of thin linear antennas, see "Coupled Antennas" by C.T. Tai, in April 1948 Proceedings of the I.R.E. Those also involve multiple terms of sine and cosine integrals. Before numerical calculations became possible, many very good mathematicians and engineers devised a number of approximation methods of varying complexity and accuracy. You'll find their works in various journals primarily in the 1940s - 1960s. The complexity and difficulty of the problem is why virtually all antenna calculations are done today with computers, using numerical methods such as the moment method. In summary, here are your choices: 1. You can calculate the approximate radiation resistance but not reactance of a thin, free-space antenna by assuming a sinusoidal current distribution and using the method Reg described. To include the effect of ground, you have to calculate or look up from a table the mutual impedance between the antenna and its "image", and modify the feedpoint impedance accordingly by applying the mesh equations for two coupled antennas. This method of including the effect of ground becomes inaccurate below around 0.2 wavelength, if the antenna is over typical earth. 2. You can use various approximation methods to calculate reactance, and resistance with better accuracy. But for the effect of ground, you're still limited to being greater than about 0.2 wavelength high. 3. To accurately include the effect of real ground with low antennas, and/or to get resistance and reactance values with arbitrarily good accuracy requires numerical methods. A computer program is the only practical way to do this. A very good basic description of the moment method can be found in the second and later editions of Kraus' _Antennas_. [*] Cin(x) = ln(gamma * x) - Ci(x), where gamma = Euler's constant, 0.577. . . Ci(x) = the integral from -infinity to x of [cos(v)/v dv] = ln(gamma * x) - (x^2)/(2!2) + (x^4)/(4!4) - (x^6)/(6!6). . . Roy Lewallen, W7EL Harry wrote: > Hi Tim and Reg, > > Thank you for your valuable information. Is there any website or > textbook that actually shows the step-by-step calculation of this magic > number which has been quoted so often in the cable industry? > > You know most video cables and connectors have characteristic > impedance, 75 Ohms. > > I am not afraid of math. I just like to understand the details of its > derivation. > > -- Harry > Article: 217126 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: 73 Ohms, How do you get it? Date: Wed, 14 Sep 2005 00:49:52 +0000 (UTC) Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126653287_28145@spool6-east.superfeed.net> "Cecil Moore" wrote > Prad is found by integrating the Poynting Vector over a > certain radius. ==================================== Cec, what's the Poynting Vector? --- Reg. Article: 217127 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: how to model a loaded vertical ?? Date: Tue, 13 Sep 2005 17:51:23 -0700 Message-ID: <11iet0fapmh7pd2@corp.supernews.com> References: <11i7obsivh8u3c1@corp.supernews.com> <4324780B.9010904@comcast.net> <1126467122_10775@spool6-east.superfeed.net> dansawyeror wrote: > All, > > Thank you for your help to get the basic model in place. It seems to be > working except that ground resistance does not appear to be modeled. > This may be an oversimplification my part in how the source is defined > or connected. It is a simple source connected to the first, lower, > segment. The end of that segment is also connected to a radial system of > 8 quite short radials. I would expect to see the feedpoint impedance > reflect the ground system. However, it seems to reflect the vertical > element only. That value is very close to a theoretical loaded element > over a perfect ground. This ground is a medium ground so it should have > some visible effect. > > Is it obvious what am I doing wrong? It sounds like you're using a MININEC-type ground, which isn't appropriate for this application. Be sure to read the manual sections involving ground modeling. Roy Lewallen, W7EL Article: 217128 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: how to model a loaded vertical ?? Date: Tue, 13 Sep 2005 17:53:16 -0700 Message-ID: <11iet3vqf6q5mf8@corp.supernews.com> References: <11i7obsivh8u3c1@corp.supernews.com> <4324780B.9010904@comcast.net> dansawyeror wrote: > > On the SWR scan is there a way to print or plot the step outputs? I am > trying to determine the resonance point. The SWR scan automatically produces a plot. To print, click File, then Print in the SWR display window. Roy Lewallen, W7EL Article: 217129 of rec.radio.amateur.antenna From: "Bill Turner" Subject: Re: 73 Ohms, How do you get it? Date: 14 Sep 2005 00:54:52 GMT Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> Reg Edwards wrote: > There's no such value as 'exact'. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Nonsense. I have exactly two pencils in my pencil holder. :-) 73, Bill W6WRT Article: 217130 of rec.radio.amateur.antenna From: richardharrison@webtv.net (Richard Harrison) Subject: Re: best HF antenna system next to a trailer? Date: Tue, 13 Sep 2005 20:29:31 -0500 Message-ID: <3627-43277CFB-102@storefull-3253.bay.webtv.net> References: Bill Turner wrote: "Without more information, this comparison is flawed." I agree the information was incomplete. I dfid not reproduce the whole article. The fault was mine, not Phil`s. A low dipole has a high radiation angle. For comparison, Phil was working Airstream net stations in New York, New Jersey, Maryland, Pennsylvania, Ohio, and New England. Phil was located in Ontario near Buffalo, New York when he collected his data. His in-laws lived there. Phil`s home QTH at the time was the highest spot in Western Connecticut, with a line-of-sight path to New York City. Phil had surrounded his mountain top with rhombic antennas pointed toward his likely targets. Amateurs answered when he called. In the Airstream net, most of the contacts were made Sundays on 3963 kHz at 8 am local time. Sky wave was mostly near vertical incidence. The low dipole was good for the job. Not too directional and a lot of radiation nearly straight up. Phil noted that several times when he switched to to the mobile whip, he could not be heard through the QRM. The numbers Phil put in Table 3 are only true under the conditions prevailing when he made the checks. Best regards, Richard Harrison, KB5WZI Article: 217131 of rec.radio.amateur.antenna From: Marshall Goldblatt Subject: Re: How to weather-seal an upside down Tailtwister rotor? Date: Tue, 13 Sep 2005 21:40:18 -0400 Message-ID: <3opd8pF71npnU1@individual.net> References: <3op5feF73ibjU1@individual.net> Dan/W4NTI wrote: > "Marshall Goldblatt" wrote in message > news:3op5feF73ibjU1@individual.net... > >>Hello all, >> >>I have a Tailtwister (TX-2) rotor mounted on a Rohn 25 foldover tower. >>While the tower itself appears to have survived intact, hurricane >>Katrina snapped the mast and destroyed the antennas. I need to fold the >>tower over to work in it, and likely leave it folded over for a fairly >>extended period. This will leave the top of the tower and the rotor >>upside down. Unfortunately, it is still the rainy season here, and the >>last time I needed to do this, rain water got into the rotor and settled >>in the bell, causing rust and other corrosion damage inside the rotor, >>because it is only weather protected when it is upright. I would like >>to seal the rotor to prevent this from happening again, but none of the >>ideas I've had so far (wrapping it in plastic garbage bags, using duct >>tape, using sealing foam) are usable, either because they don't seal >>well enough to keep water out or because stuff may get up inside the >>rotor where I can't get it out. >> >>So, does anyone have any suggestions? >> >>73, Marshall - W4EMB >> >> > > > Maybe ... get some axle grease, or RTV sealant would be better, perhaps. > Both should peal off reasonable well. > > One other thing I am concerned with tho. I always heard that the rotar > must be kept in a vertical position or the grease would drain out of the > bearings? Wives tale ??? I don't know. But I always keep mine vertical > when stored. Don't know about that, but there's no way to keep the rotor vertical when lowering a foldover tower... In any case, it's been folded over (for long periods) many times, and I've never noticed a bearing problem. Article: 217132 of rec.radio.amateur.antenna From: Bob Bob Subject: Re: How to weather-seal an upside down Tailtwister rotor? References: <3op5feF73ibjU1@individual.net> Message-ID: <6pakv2-ti9.ln1@p400bob.personal.cox.net> Date: Tue, 13 Sep 2005 20:25:25 -0500 One of the tricks I learnt early on with RTV sealant in medical ultrasound water tanks is if you wet the surfaces with water and a detergent wetting agent the sealant wont actually adhere to the prewetted surface. Kind of handy if you wanted to force the sealant into a clearance slot and remove it later. Or was it oil? Damn I cant remember! I know kerosene is used to pre the surface for better adhesion... How about paper/masking tape over the gaps and spraying with that gluggy sealant you use on sink drains? Probably not very useful thoughts, sorry! Cheers Bob W5/VK2YQA Dan/W4NTI wrote: > > Maybe ... get some axle grease, or RTV sealant would be better, perhaps. > Both should peal off reasonable well. > > One other thing I am concerned with tho. I always heard that the rotar > must be kept in a vertical position or the grease would drain out of the > bearings? Wives tale ??? I don't know. But I always keep mine vertical > when stored. > > Dan/W4NTI > > Article: 217133 of rec.radio.amateur.antenna From: "Roger Leone" References: Subject: Re: Balanced from unbalanced via a 100 ohm Q section Message-ID: <2ALVe.715$Jm.384@newssvr27.news.prodigy.net> Date: Wed, 14 Sep 2005 02:05:50 GMT "Bob Bob" wrote in message news:g46jv2-ib6.ln1@p400bob.personal.cox.net... > Hi Roger > > Might get around to it today! (Being unemployed is sometimes fun..) > Bob: If your 100 ohm Q section doesn't work out as expected, I have lots of RG-71 (93 ohm) coax that might be worth trying. Let me know if you are interested. 73, Roger Article: 217134 of rec.radio.amateur.antenna From: "RST Engineering" Subject: Re: Corrosion on aluminum antenna Date: Tue, 13 Sep 2005 19:06:54 -0700 Message-ID: <11if1e3fd2r81cc@corp.supernews.com> References: <24snh19iu141gghh6iamqv9peh8q7649gd@4ax.com> <0v-dnX_XAvtEJoLeRVn-rA@comcast.com> <313030303837383543232DCF97@zetnet.co.uk> > Is tin worm like ... Bronze Bitch Borers? I've met a few of them in my time... Jim Article: 217135 of rec.radio.amateur.antenna From: nospam@nouce.bellatlantic.net Subject: Re: best HF antenna system next to a trailer? Message-ID: References: <1126505259.234971.15970@f14g2000cwb.googlegroups.com> <9175-4326EEA5-1@storefull-3254.bay.webtv.net> Date: Wed, 14 Sep 2005 02:11:13 GMT On 13 Sep 2005 16:15:08 GMT, "Bill Turner" wrote: >Richard Harrison wrote: > >> Phil found a simple dipole only a few feet above ground would >> outperform a mobile whip on 40 or 75 meters. >~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > >Without more information, this comparison is flawed. A mobile whip has >a lower angle of radiation than a horizontal dipole. On 40 or 75, the >vertical component of radiation can be quite significant for close-in >stations (100 miles or so). At night, working long distances, the whip >may outperform the dipole. During the day, the dipole will probably >outperform the whip. > >It all depends. >73, Bill W6WRT Correct on radiation angle, however the average mobile whip at 3.8mhz is around 10% efficient. Even at 7Mhz it doesn't improve much efficientcy wise. The low dipole (low being less than .25WL) is close or better than 95% efficient but has a rotten radiation angle for DX however close in it will be very good. Myself in that situation.. I'd put a poles at either end of the trailer (thats 50ft length) and if possible get it up 30ft or better and hang a dipole. If the antenna is 66' (40m) the excess length can hang. The support poles can be anything that will stay up. At 20m 30ft is 1/2WL up and will be decent. Even if you can't do two support poles and only one make that one high as possible and mount a dipole as a sloper. It will be somewhat directional but performace will be far better than any ground mounted vertical that has no ground plane. If money wasn't a limiting factor. put down a base and put up a freestanding tower. The rules remain. More metal, higher the better. Allison KB1GMX Article: 217136 of rec.radio.amateur.antenna Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article From: Cecil Moore Date: Tue, 13 Sep 2005 21:31:51 -0500 Message-ID: <1126665270_28245@spool6-east.superfeed.net> References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <6qudnRtjVJhVpLveRVn-tQ@comcast.com> <0ICdncTJkPKeVrveRVn-vA@comcast.com> <30DVe.1556$Nw6.692@bignews6.bellsouth.net> <88WdnbrHqZgpkbreRVn-tg@comcast.com> <4327720A.61F01CAB@earthlink.net> Michael A. Terrell wrote: > Its just too damn bad you can't tar and feather them and then run > them out of town, like the good old days! ;-) Seems to me a large percentage of the blame lies with the buyers who readily agree to such irrational HOA terms and then complain about them later. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Article: 217137 of rec.radio.amateur.antenna Subject: Re: 73 Ohms, How do you get it? From: Cecil Moore Date: Tue, 13 Sep 2005 21:45:48 -0500 Message-ID: <1126666107_28257@spool6-east.superfeed.net> References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126653287_28145@spool6-east.superfeed.net> Reg Edwards wrote: > "Cecil Moore" wrote > >>Prad is found by integrating the Poynting Vector over a >>certain radius. > > Cec, what's the Poynting Vector? Same thing as a power flow vector. The dimensions are energy per second per unit area. If the power flow vector is integrated over the entire surface of a sphere of radius r, the result is total radiated power. I thought maybe you and Mr. Poynting might have worked together at some time in the 20th century. :-) > Poynting, John Henry (1852-1914) > English physicist, mathematician, and inventor. He devised > an equation by which the rate of flow of electromagnetic energy > (now called the Poynting vector) can be determined. http://www.cartage.org.lb/en/themes/Biographies/MainBiographies/P/Poynting/1.html -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Article: 217138 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: 73 Ohms, How do you get it? Date: Wed, 14 Sep 2005 03:31:24 +0000 (UTC) Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> "Reg Edwards" wrote > It is equally correct to say that the radiation resistance of a dipole > is 2*73 = 146 ohms, since this is the value when the radiation > resistance is assumed to be uniformly distributed along its length as > is the conductor resistance. > > For calculating purposes the radiation and conductor resistances can > simply be added together. ===================================== Hints and tips - By the same arithmetical reasoning - The centre feedpoint input resistance of a 1/2-wave dipole is 73 ohms plus HALF of the conductor end-to-end HF resistance, which to be precise sometimes matters. This is exact insofar as 73 is exact - not an approximation. The HF resistance of a copper wire at 20 degrees C is - Rhf = Sqrt( F ) / 12 / d ohms per metre, Where F is the frequency in MHz and d is the wire diameter in millimetres. For example, the end-to-end loss resistance of a 1/2-wave dipole at 1.9 MHz using 16-gauge copper wire is 7.07 ohms, which increases the feedpoint resistance to 73 + 3.53 = 76.53 ohms, to give a radiating efficiency of 95.4 percent. Some people would consider that's enough to lose a contest! Why not start a little notebook to record useful, simple, little formulae such as above which don't appear in Terman et al? Or if they do appear then you can never find the right page in the right volume. ---- Reg. Article: 217139 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: best HF antenna system next to a trailer? Date: Tue, 13 Sep 2005 20:43:23 -0700 Message-ID: <11if72vgu1uln04@corp.supernews.com> References: <1126505259.234971.15970@f14g2000cwb.googlegroups.com> <9175-4326EEA5-1@storefull-3254.bay.webtv.net> An antenna doesn't have a single "radiation angle". It radiates at all angles. The relevant question is how much does it radiate at the particular angle of interest, not at which angle does it radiate the most. An antenna which radiates its maximum at a high angle might well radiate more at a low angle than an antenna with a lower angle of maximum radiation. Roy Lewallen, W7EL nospam@nouce.bellatlantic.net wrote: > On 13 Sep 2005 16:15:08 GMT, "Bill Turner" wrote: >> >>Without more information, this comparison is flawed. A mobile whip has >>a lower angle of radiation than a horizontal dipole. . . > > Correct on radiation angle . . . Article: 217140 of rec.radio.amateur.antenna From: "Joel" Subject: Yet another grounding question Date: Tue, 13 Sep 2005 22:49:27 -0500 Message-ID: After almost 50 years banging around Ham Radio I finely have my tower up.. I have each leg of the tower grounded with 2 inch copper strapping , each to their own ground rod.Those ground rods are all connected together and run off to another ground rod I will use that as a common ground. All the coax that come into the house goes to a outside 5x5 box that has poliphaseres installed in it. The box is brass lined and the brass is lapped to another 2 inch copper strap that goes to the common ground. The station ground is separate until it gets to the common ground.. With all this said,I have a questions.. - I 'should' have the power entrance ground run over to the common ground. But it's over 90 feet away and the house has plastic water pipes.. Does it make sense to run a copper wire or strap that far? If so, should it be berried all the way or run exposed. It seems to me the impedance would be so high in the run, that it would be a waste of copper? TNX Joe AG4QC Article: 217141 of rec.radio.amateur.antenna From: Owen Duffy Subject: Re: loop inductance calculation? Message-ID: References: <6odfi1l8k7bnerl8fucbbbdg17c3mtqg11@4ax.com> Date: Wed, 14 Sep 2005 06:01:17 GMT On Wed, 14 Sep 2005 01:42:03 -0400, TRABEM <> wrote: >What's the approximate inductance for a single turn square loop, 10 >feet per side in free space (if that matters)? There should be an easy >way to calculate this, maybe there is, but I'm not aware of it. > http://www.technick.net/public/code/cp_dpage.php?aiocp_dp=util_inductance_square -- Article: 217142 of rec.radio.amateur.antenna From: David Subject: Open Stub fed J antenna Message-ID: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> Date: Wed, 14 Sep 2005 06:21:54 GMT Does anyone know of where I could find an example of a homebrew open stub fed j antenna. I want to construct a unit for 915 MHz using SMA plug and coaxial cable. Thanks in advance Article: 217143 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: 73 Ohms, How do you get it? Date: Tue, 13 Sep 2005 23:36:35 -0700 Message-ID: <11ifh7o30m2sfca@corp.supernews.com> References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> <11iesohk2gnkf80@corp.supernews.com> <1126670159.827784.237990@g47g2000cwa.googlegroups.com> Harry wrote: > Hi Roy, > > Thanks for all the valuable information. Are you a professor? Not by a long shot. I'm way too poor a student to ever be considered for a job as a teacher. > You may want to write a book titled "Story of the 73 Ohms". It's already been written, by many people who know a great deal more than I. Roy Lewallen, W7EL Article: 217144 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: how to model a loaded vertical ?? Date: Tue, 13 Sep 2005 23:41:08 -0700 Message-ID: <11ifhg8s81ven91@corp.supernews.com> References: <11i7obsivh8u3c1@corp.supernews.com> <4324780B.9010904@comcast.net> <1126467122_10775@spool6-east.superfeed.net> <11iet0fapmh7pd2@corp.supernews.com> <4327A068.6060106@comcast.net> dansawyeror wrote: > Roy, > > Thanks, I did and I have tried all the combinations. > > I would suspect that 'free space' would show a mis match for 'short > radials'. It does not. Simulations of free space dipoles seem accurate. > Am I missing something? You'll need to send me the model description (.EZ file) so I can see what you've got. Attach it to an email to me. > I also tried to simulate several values of real earth. None of them > produced high input impedance values. What ground values represent > suburban clay? We have clay here, and by comparing a dipole and vertical at various times of year, I've estimated that the soil is about equivalent to EZNEC's "poor" quality ground in the summer when it's bone dry and "very good" ground in the winter when soaking wet. It's an approximation at best, though. Roy Lewallen, W7EL Article: 217145 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: loop inductance calculation? Date: Tue, 13 Sep 2005 23:44:35 -0700 Message-ID: <11ifhmngeb6au21@corp.supernews.com> References: <6odfi1l8k7bnerl8fucbbbdg17c3mtqg11@4ax.com> The free demo version of EZNEC (http://eznec.com) will tell you. Choose a low frequency where the loop is electrically very small. Put a source anywhere in the loop and look at the Source Data. It'll give you the reactance which you can convert to inductance at the frequency you chose. The inductance should stay fairly constant with frequency as long as the frequency is low enough that the loop circumference is a very small part of a wavelength. Roy Lewallen, W7EL TRABEM wrote: > What's the approximate inductance for a single turn square loop, 10 > feet per side in free space (if that matters)? There should be an easy > way to calculate this, maybe there is, but I'm not aware of it. > > Thanks > > T Article: 217146 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: loop inductance calculation? Date: Tue, 13 Sep 2005 23:55:48 -0700 Message-ID: <11ifibocus6c2e1@corp.supernews.com> References: <6odfi1l8k7bnerl8fucbbbdg17c3mtqg11@4ax.com> TRABEM wrote: > > What's the relative permeability of air?? "Relative permeability" is the permeability relative to that of free space. The relative permeability of any non-magnetic material, including air, is 1. > > They give this statement on the help page, but I don't understand what > it means. > > Note: µ0 = 4¶·10-7 [Hm-1] (Absolute Permeability) The permeability of free space (µ0) is 4 * pi * 10^-7 webers/amp-m (MKSA units). The permeability (µ) of anything is its relative permeability (µr) times µ0. Roy Lewallen, W7EL Article: 217147 of rec.radio.amateur.antenna From: nospam@nouce.bellatlantic.net Subject: Re: best HF antenna system next to a trailer? Message-ID: References: <1126505259.234971.15970@f14g2000cwb.googlegroups.com> <9175-4326EEA5-1@storefull-3254.bay.webtv.net> <11if72vgu1uln04@corp.supernews.com> Date: Wed, 14 Sep 2005 12:00:22 GMT On Tue, 13 Sep 2005 20:43:23 -0700, Roy Lewallen wrote: >An antenna doesn't have a single "radiation angle". It radiates at all >angles. The relevant question is how much does it radiate at the >particular angle of interest, not at which angle does it radiate the >most. An antenna which radiates its maximum at a high angle might well >radiate more at a low angle than an antenna with a lower angle of >maximum radiation. > >Roy Lewallen, W7EL Hello Roy, I do understand that. I also understand when you say radiation angle your talking about the primary or dominent lobe(s). There may be many other lobes at useful or less than useful angles present as well. However, how does that relate to using a shortend antenna with maybe 10% radiation efficientcy to a dipole at a reasonably attainable height? Allison KB1GMX > >nospam@nouce.bellatlantic.net wrote: >> On 13 Sep 2005 16:15:08 GMT, "Bill Turner" wrote: >>> >>>Without more information, this comparison is flawed. A mobile whip has >>>a lower angle of radiation than a horizontal dipole. . . >> >> Correct on radiation angle . . . Article: 217148 of rec.radio.amateur.antenna Subject: Re: Open Stub fed J antenna From: Cecil Moore Date: Wed, 14 Sep 2005 09:07:22 -0500 Message-ID: <1126707001_31799@spool6-east.superfeed.net> References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> David wrote: > Does anyone know of where I could find an example of a homebrew open stub > fed j antenna. I want to construct a unit for 915 MHz using SMA plug and > coaxial cable. An open stub J-pole is the same as a Zepp. 1/2WL element end fed by 1/4WL balanced series section. The coax connects to the end of the series section. Arrow Antenna makes one for 2m. Plans are available that could possibly be scaled to 915 MHz. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Article: 217149 of rec.radio.amateur.antenna From: "Richard Fry" References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> <11iesohk2gnkf80@corp.supernews.com> <1126670159.827784.237990@g47g2000cwa.googlegroups.com> Subject: Re: 73 Ohms, How do you get it? Date: Wed, 14 Sep 2005 09:22:19 -0500 Message-ID: <43283245_3@newsfeed.slurp.net> "Harry" wrote about Roy Lewallen: > You may want to write a book titled "Story of the 73 Ohms". ___________ It should include the point that the 73 ohm radiation resistance value applies to a physical 1/2-wave, thin-wire, linear dipole in free space, and that a reactance term of + j42.5 ohms also applies to such a configuration (Kraus 3rd Edition, p. 182). The dipole length needs to be shorted by a few percent in order to zero out the reactance term, at which time the resistance term will be about 65 ohms. RF Article: 217150 of rec.radio.amateur.antenna From: "W5GT" Subject: WTB: 40' self supporting tower in Dallas area Message-ID: Date: Wed, 14 Sep 2005 10:02:02 -0500 I'm looking for a 40' tower in the Dallas area. Rohn 25 or Universal OK. I'd prefer that the tower is down. If rotor / and or beam available will consider. 73s Dave - W5GT w5gt@arrl.net Article: 217151 of rec.radio.amateur.antenna From: Bob Miller Subject: Re: best HF antenna system next to a trailer? Message-ID: References: <1126505259.234971.15970@f14g2000cwb.googlegroups.com> <9175-4326EEA5-1@storefull-3254.bay.webtv.net> <1126670383.884527.133320@f14g2000cwb.googlegroups.com> Date: Wed, 14 Sep 2005 15:44:33 GMT On 13 Sep 2005 20:59:43 -0700, eternalsquire@comcast.net wrote: >Money and space are actually limiting factors, but at least CC&R's >arent! My wife and I have been discussing this, and she really >doesn't like the idea of something 30 to 40 feet high on a small lot. > ...excerpted... > >I think because space, money, and aesthetics are limiting factors, I >need to use precision to my advantage rather than size or height, and a >4 square may help there. > >Comments? > >The Eternal Squire Any reason you're not considering a 20 meter dipole, fed with ladderline to a tuner, for 20 thru 10 meters? Put it 25 feet high, and it's nearly or more than a half wave high on all bands. bob k5qwg Article: 217152 of rec.radio.amateur.antenna From: "Bill Turner" Subject: Re: best HF antenna system next to a trailer? Date: 14 Sep 2005 15:35:43 GMT Message-ID: References: <1126505259.234971.15970@f14g2000cwb.googlegroups.com> <9175-4326EEA5-1@storefull-3254.bay.webtv.net> <11if72vgu1uln04@corp.supernews.com> Roy Lewallen wrote: > > An antenna doesn't have a single "radiation angle". It radiates at > all angles. The relevant question is how much does it radiate at the > particular angle of interest, not at which angle does it radiate the > most. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ That's true, except few if any hams have a specific "angle of interest", since different angles are used at different times. For most of us, the angle of maximum radiation gives a general indication of how the antenna will perform. A better indication would be a graphical representation. It's always a problem when one tries to reduce a complex situation like this down to a single number. 73, Bill W6WRT Article: 217153 of rec.radio.amateur.antenna From: John - KD5YI Subject: Re: Help required to identify antenna type References: Message-ID: Date: Wed, 14 Sep 2005 16:01:23 GMT > "David" wrote in message > news:v5zVe.42161$FA3.13896@news-server.bigpond.net.au... > >>Hi, >> >>I have a Whip antenna that is supposed to give 3dB "gain" at 915MHz. >>After pulling the unit apart and studying the construction, I am not sure >>what style of antenna this is. >> >>The antenna consists of an SMA plug that has RF178 cable soldered to >>centre pin and >>it appears earth braid is connected to ground side of plug. >> >>The cable goes up the inside of 1 6mm Nylon tube for 40mm and then >>exits the tube and winds around 4.5T. It then enters the tube >>again and runs another 80mm. At this point the earth braid is stripped >>leaving only the centre conductor and dielectric to continue another 70mm >>to the top of the Radome (Nylon tube). >> >>I understand the construction of 5/8 antenna but I would not expect the >>braid to be earthed. >> >>Thanks in advance for any help. >> >>Regards >> >>David > Paul P wrote: > Could you post pictures on the binaries or email them to me please? I would > like to see this. > > Thanks in advance, > Paul. > > p.pinyot [at] worldnet [dot] att [dot] net > Hi, Paul - If you have the 2004 ARRL Handbook, the antenna is described on page 20.17 as a resonant feed-line dipole. The figure on that page shows its construction. If you do not have the handbook, I can scan the page and send it to you. Regards, John Article: 217154 of rec.radio.amateur.antenna From: "Jerry" References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <6qudnRtjVJhVpLveRVn-tQ@comcast.com> <0ICdncTJkPKeVrveRVn-vA@comcast.com> <30DVe.1556$Nw6.692@bignews6.bellsouth.net> <88WdnbrHqZgpkbreRVn-tg@comcast.com> <4327720A.61F01CAB@earthlink.net> Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Message-ID: Date: Wed, 14 Sep 2005 12:45:26 -0400 "Michael A. Terrell" wrote in message news:4327720A.61F01CAB@earthlink.net... > > > As someone who lives near Ocala and has to visit a lot of these gated > communities run by HOAs, I find most of them to be jerks who are only > interested in holding onto their perceived power at any cost. The fact > that it hurts others doesn't matter to them. Another HOA in the area > told a retired couple move out, or send their 17 year old grand daughter > away after she lost both of her parents in an accident. She had a few > months till she was to graduate from high school and no other relatives > but it didn't matter to the HOA. People like that are scum, no matter > how expensive their home, or what they drive. > > Its just too damn bad you can't tar and feather them and then run > them out of town, like the good old days! ;-) > > -- > ? > > Michael A. Terrell > Central Florida I am actually quite peaceable and believe in living and letting live in most cases. Who I allow in my home is up to me and whom I refuse entry is not the purvey of HOA Nazis. And, again, it is why I chose an older home (1956) with plenty of room, almost ZERO crime, and NO HOA's. Now should I run into one of those SOB's that start telling me what I can or can't do, then it will become another story. I feel so strongly about property rights that I would go to WAR over it, both nationally...or on a personal basis. Like, I wouldn't be averse to whuppin' some smartmouth's you-know-what over it. Again, being very quiet and peaceable as I certainly am, I am also quite intimidating in stature, so it would be an interesting fight! LOL! Now, it *could* even get down to the point of "You SOB, you can tell me what to do when you get around on the backside of my shotgun, or you got enough a$$ on ya to MAKE me, you *&^%$#"! LMAO! In Charlotte, NC, this year, there was a case where the HOA Nazis and their powermongers went too far with "foreclosures" and the NC legislature put some restrictions on their ability to foreclose with respect to their "rules". Now, foreclosing on someone's house because some Nazi b#####d didn't LIKE the peoples' guests? NOT! (Not me because I don't HAVE that problem) I can see how this could cause somebody to get severely injured or KILLED! You don't MESS with one's home! :( I feel for those who have to put up with such nonsense! OTH, one should NEVER move into such a place, either, so he bears some of the blame. :) Best to all, Jerry Article: 217155 of rec.radio.amateur.antenna From: "nitram578" Subject: FS: KLM 10-4 10 meter beam NIB Message-ID: Date: Wed, 14 Sep 2005 12:50:40 -0500 For sale a NIB KLM 10-4 (4 element 10 meter beam) $100.00 plus shipping. Article: 217156 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: how to model a loaded vertical ?? Date: Wed, 14 Sep 2005 11:25:00 -0700 Message-ID: <11igqo08d5rp800@corp.supernews.com> References: <11i7obsivh8u3c1@corp.supernews.com> <4324780B.9010904@comcast.net> <11iet3vqf6q5mf8@corp.supernews.com> Ham op wrote: > Roy, if he reads the impedance value he can determine resonance by the > absence of the reactive term. > > Do you agree that the SWR scan is a poor method of determining resonance? No, I usually use the SWR sweep to determine resonance. Stepping the cursor and looking at the impedance at each step quickly identifies the resonant frequency to within the closest step. Additional narrower scans are done as necessary to get more precision. What method do you use that's better? Roy Lewallen, W7EL Article: 217157 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: best HF antenna system next to a trailer? Date: Wed, 14 Sep 2005 11:28:05 -0700 Message-ID: <11igqtpiih2553a@corp.supernews.com> References: <1126505259.234971.15970@f14g2000cwb.googlegroups.com> <9175-4326EEA5-1@storefull-3254.bay.webtv.net> <11if72vgu1uln04@corp.supernews.com> <1126715019.030393.275490@o13g2000cwo.googlegroups.com> nm5k@wt.net wrote: > A better indication would be a > graphical representation. > > The EZNEC demo does that well. There is a little green ball > that you can grab with your mouse, and place it at any angle > you wanna check. Makes it quite easy to see, or compare > various angles. MK > Better yet, you can superimpose the plots from two antennas for direct comparison. In v. 4.0, you can even get a numerical readout of the difference between the two in dB at the angle of the cursor (the little green ball). Roy Lewallen, W7EL Article: 217158 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: best HF antenna system next to a trailer? Date: Wed, 14 Sep 2005 11:31:49 -0700 Message-ID: <11igr4q450p1d7e@corp.supernews.com> References: <1126505259.234971.15970@f14g2000cwb.googlegroups.com> <9175-4326EEA5-1@storefull-3254.bay.webtv.net> <11if72vgu1uln04@corp.supernews.com> nospam@nouce.bellatlantic.net wrote: > On Tue, 13 Sep 2005 20:43:23 -0700, Roy Lewallen > wrote: > > >>An antenna doesn't have a single "radiation angle". It radiates at all >>angles. The relevant question is how much does it radiate at the >>particular angle of interest, not at which angle does it radiate the >>most. An antenna which radiates its maximum at a high angle might well >>radiate more at a low angle than an antenna with a lower angle of >>maximum radiation. >> >>Roy Lewallen, W7EL > > > Hello Roy, > > I do understand that. I also understand when you say radiation angle > your talking about the primary or dominent lobe(s). There may be > many other lobes at useful or less than useful angles present as well. > > However, how does that relate to using a shortend antenna with maybe > 10% radiation efficientcy to a dipole at a reasonably attainable > height? > > Allison > KB1GMX The context was that one antenna was better for DX than the other because it had a "lower radiation angle". An antenna with a "low radiation angle" which is 10% efficient probably radiates less at low angles than a more efficient antenna with a "high radiation angle". Therefore it's not a better DX antenna. My point is simply that the angle of maximum radiation is not a valid criterion for comparing antennas. Roy Lewallen, W7EL Article: 217159 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: best HF antenna system next to a trailer? Date: Wed, 14 Sep 2005 11:37:42 -0700 Message-ID: <11igt81c682aheb@corp.supernews.com> References: <1126505259.234971.15970@f14g2000cwb.googlegroups.com> <9175-4326EEA5-1@storefull-3254.bay.webtv.net> <11if72vgu1uln04@corp.supernews.com> Bill Turner wrote: > Roy Lewallen wrote: > > >>An antenna doesn't have a single "radiation angle". It radiates at >>all angles. The relevant question is how much does it radiate at the >>particular angle of interest, not at which angle does it radiate the >>most. > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > That's true, except few if any hams have a specific "angle of > interest", since different angles are used at different times. For > most of us, the angle of maximum radiation gives a general indication > of how the antenna will perform. A better indication would be a > graphical representation. It's always a problem when one tries to > reduce a complex situation like this down to a single number. > > 73, Bill W6WRT I agree, which is why EZNEC produces a graphical output. I encourage people to look at it rather than reducing the pattern to a single number. And I have to emphasize once again that what really counts is the field strength, not the pattern shape. An antenna can have a wonderful looking pattern with nearly all its radiation at low angles, and still be a poor antenna for DX. Or with nearly all its radiation at high angles and be a poor antenna for short range communications. One familiar example is a Beverage antenna, which has a lovely pattern shape but makes a poor transmitting antenna. A quarter wave vertical will nearly always do much better for transmitting, even at the angles favored by the Beverage. Roy Lewallen, W7EL Article: 217160 of rec.radio.amateur.antenna From: "Frank" References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> <11iesohk2gnkf80@corp.supernews.com> Subject: Re: 73 Ohms, How do you get it? Message-ID: Date: Wed, 14 Sep 2005 20:30:28 GMT "Roy Lewallen" wrote in message news:11iesohk2gnkf80@corp.supernews.com... > Just about any antenna textbook will show you the calculation of a half > wavelength, infinitely thin dipole in free space. For that special case, > the answer ends up being simply 30 * Cin(2 * pi), where Cin is a > modification of the cosine integral Ci[*]. That's where the "magic number" > comes from. Kraus' _Antennas_ is just one of the many textbooks which give > the derivation for this. It takes about 3 pages and 23 equations for Kraus > to derive. > > One assumption made in calculation of this value is that the current > distribution is sinusoidal, an assumption that's true only for an > infinitely thin antenna. For finite thickness wire, the calculation > becomes much more difficult. The radiation resistance changes only slowly > with wire diameter, however, so sinusoidal distribution is a reasonably > good approximation provided that the antenna is thin. Feedpoint reactance, > though, varies much more dramatically with both antenna length and > diameter. Calculating its value exactly requires solution of a triple > integral equation which can't be solved in closed form. That's why > computer programs are used to solve it numerically. > > To include the effect of ground, you need to calculate the mutual > impedance between the antenna and its "image". If the antenna is about 0.2 > wavelength above ground or higher (for a half wave antenna -- the height > must be greater if the antenna is longer), you can assume that the ground > is perfect and get a pretty good result. Below that height, the > calculation again becomes much more complicated because the quality of the > ground becomes a factor. If you're interested in the numerical methods > used, locate the NEC-2 manual (available on the web), which describes it. > > If you're satisfied with approximate results, the work by S.I. Shelkunoff > provides formulas for free-space input impedance of antennas with finite > diameter wire which can be solved with a programmable calculator or > computer. They're detailed in "Theory of Antennas of Arbitrary Size and > Shape", in Sept. 1941 Proceedings of the I.R.E. The formulas for R and X > contain many terms involving sine and cosine integrals, which can be > approximated with numerical series. You'll find additional information in > his book _Advanced Antenna Theory_. For approximate calculations of mutual > impedance of thin linear antennas, see "Coupled Antennas" by C.T. Tai, in > April 1948 Proceedings of the I.R.E. Those also involve multiple terms of > sine and cosine integrals. > > Before numerical calculations became possible, many very good > mathematicians and engineers devised a number of approximation methods of > varying complexity and accuracy. You'll find their works in various > journals primarily in the 1940s - 1960s. > > The complexity and difficulty of the problem is why virtually all antenna > calculations are done today with computers, using numerical methods such > as the moment method. > > In summary, here are your choices: > > 1. You can calculate the approximate radiation resistance but not > reactance of a thin, free-space antenna by assuming a sinusoidal current > distribution and using the method Reg described. To include the effect of > ground, you have to calculate or look up from a table the mutual impedance > between the antenna and its "image", and modify the feedpoint impedance > accordingly by applying the mesh equations for two coupled antennas. This > method of including the effect of ground becomes inaccurate below around > 0.2 wavelength, if the antenna is over typical earth. > > 2. You can use various approximation methods to calculate reactance, and > resistance with better accuracy. But for the effect of ground, you're > still limited to being greater than about 0.2 wavelength high. > > 3. To accurately include the effect of real ground with low antennas, > and/or to get resistance and reactance values with arbitrarily good > accuracy requires numerical methods. A computer program is the only > practical way to do this. A very good basic description of the moment > method can be found in the second and later editions of Kraus' _Antennas_. > > [*] Cin(x) = ln(gamma * x) - Ci(x), where gamma = Euler's constant, 0.577. > . . Ci(x) = the integral from -infinity to x of [cos(v)/v dv] = ln(gamma * > x) - (x^2)/(2!2) + (x^4)/(4!4) - (x^6)/(6!6). . . > > Roy Lewallen, W7EL Very interesting references. In particular Kraus' 2nd ed. pp 359 - 408. Also Stutzman and Thiele, 1st ed. pp 306 - 374. Pretty much grad level, needs effort, (for me) even though I took Stutzman and Thiele's antenna course in 1998 (NCEE). Regards, Frank Article: 217161 of rec.radio.amateur.antenna From: "Frank" References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126653287_28145@spool6-east.superfeed.net> <1126666107_28257@spool6-east.superfeed.net> Subject: Re: 73 Ohms, How do you get it? Message-ID: Date: Wed, 14 Sep 2005 20:34:41 GMT >> Cec, what's the Poynting Vector? > > Same thing as a power flow vector. The dimensions are > energy per second per unit area. If the power flow vector > is integrated over the entire surface of a sphere of radius > r, the result is total radiated power. I thought maybe you > and Mr. Poynting might have worked together at some time in > the 20th century. :-) > >> Poynting, John Henry (1852-1914) >> English physicist, mathematician, and inventor. He devised an equation by >> which the rate of flow of electromagnetic energy > > (now called the Poynting vector) can be determined. S = E X H Article: 217162 of rec.radio.amateur.antenna From: Ian Jackson Subject: Re: 73 Ohms, How do you get it? Date: Wed, 14 Sep 2005 21:39:25 +0100 Message-ID: <5MOAq4S9pIKDFwB+@g3ohx.demon.co.uk> References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> In message <1126655181_28167@spool6-east.superfeed.net>, Cecil Moore writes >Reg Edwards wrote: >> Antenna conductors ARE transmission lines and the same sort of >> calculations apply. > >You're right, Reg. Without reflections from the ends of a >dipole, the feedpoint impedance would be hundreds of ohms. >A standing wave antenna is like a lossy transmission line >where the loss is to radiation. And the SWR on a 1/2WL dipole >standing wave antenna is quite high - in the neighborhood of >20:1. Just a quick question. What is the impedance at the centre of an infinitely long dipole (in free space)? Ian. -- Article: 217163 of rec.radio.amateur.antenna Subject: Re: 73 Ohms, How do you get it? From: Cecil Moore Date: Wed, 14 Sep 2005 16:42:53 -0500 Message-ID: <1126734334_299@spool6-east.superfeed.net> References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> <1126655181_28167@spool6-east.superfeed.net> <5MOAq4S9pIKDFwB+@g3ohx.demon.co.uk> Ian Jackson wrote: > Just a quick question. > What is the impedance at the centre of an infinitely long dipole (in > free space)? Same as a terminated dipole in an anechoic chamber? 600-800 ohms? -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Article: 217164 of rec.radio.amateur.antenna From: "Steve Nosko" Subject: Re: 73 Ohms, How do you get it? Date: Wed, 14 Sep 2005 16:06:10 -0500 Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> Anyway, reading the op carefully, he asked for an exact _explanation_, not an exact calculation result.. Steve, K;9.D,C'I "Bill Turner" wrote in message news:xn0e77aaf2tt5l000@cnews.newsguy.com... > Reg Edwards wrote: > > > There's no such value as 'exact'. > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > Nonsense. I have exactly two pencils in my pencil holder. :-) > > 73, Bill W6WRT Article: 217165 of rec.radio.amateur.antenna From: Owen Duffy Subject: Re: How Handle Multiple Open Wire Lines? Message-ID: References: Date: Wed, 14 Sep 2005 21:50:30 GMT Here is a commercial implementation of MF / HF transmission lines. (They are not telephone lines.) http://members-central.optushome.com.au/vk3ase/feed2.jpg http://members-central.optushome.com.au/vk3ase/feed.jpg Owen On Mon, 1 Aug 2005 17:43:34 -0700, "greg knapp 5" wrote: >I need your advice, as I have never worked with open wire lines before. >I need to feed many different antennas with open wire line and need to run >the feeline from each about 200 feet from the back pasture to the shack. I >don't want to walk out 200 feet and throw knife switches to chose the >antenna/feedline I want to feed, so I plan to run separate 600 ohm open >feeds for each antenna all the way to the shack. >The problem is I don't know what the effect is or how to handle the >multiple open wire feed lines, as they will be parallel for probably 150-200 >feet. I haven't found anything in literature describing this. >For instance, will they interact? how far do you space the feedlines from >one another? If I have 4 feedlines, can I stack them vertically or >horizontally one foot apart from each other? How much is enough separation? >What other precautions do I need? Need they be twisted if they are not near >anything other than the other feed lines? >Any help is appreciated. >73, >Greg, N6GK > -- Article: 217166 of rec.radio.amateur.antenna From: Jim Kelley Subject: Re: 73 Ohms, How do you get it? Date: Wed, 14 Sep 2005 14:38:21 -0700 Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> <1126655181_28167@spool6-east.superfeed.net> <5MOAq4S9pIKDFwB+@g3ohx.demon.co.uk> <1126734334_299@spool6-east.superfeed.net> Cecil Moore wrote: > Ian Jackson wrote: > >> Just a quick question. >> What is the impedance at the centre of an infinitely long dipole (in >> free space)? > > > Same as a terminated dipole in an anechoic chamber? 600-800 ohms? Not at zero Hz. ac6xg Article: 217167 of rec.radio.amateur.antenna From: Jim Kelley Subject: Re: 73 Ohms, How do you get it? Date: Wed, 14 Sep 2005 14:42:37 -0700 Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126653287_28145@spool6-east.superfeed.net> <1126731751.254078.115460@g49g2000cwa.googlegroups.com> Harry wrote: > Hi Cecil, > > I find another formula in Balnais book (section 4.3, 1982 edition) > for Rr: > > Rr = 20 * (pi)^2 * ( l / lamda)^2 (4-37) > > If l = lamda/2, then this formula gives Rr .=. 50 Ohms. > > (4-93) the one you quoted is > > Rr = (120*pi) / (4*pi) * Cin( 2*pi ) = 73 Ohms, (for l = lamda/2) > > where 120*pi is the intrinsic impedance for a free-space medium. > > Would you please explain the difference between these > two formulas (4-37 and 4-93)? > > > Thanks! > > -- Harry 4-37 should apparently read: Rr = 30 * (pi)^2 * (1 / lambda)^2. ac6xg Article: 217168 of rec.radio.amateur.antenna From: David Subject: Re: Open Stub fed J antenna References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <1126707001_31799@spool6-east.superfeed.net> Message-ID: Date: Wed, 14 Sep 2005 22:15:10 GMT Cecil, Thanks for the info. The open stub J looks like it should be suitable for my application being ground independent, omni directional and having low radiation angle. Cecil Moore wrote: > David wrote: > >> Does anyone know of where I could find an example of a homebrew open stub >> fed j antenna. I want to construct a unit for 915 MHz using SMA plug >> and coaxial cable. > > > An open stub J-pole is the same as a Zepp. 1/2WL element > end fed by 1/4WL balanced series section. The coax connects > to the end of the series section. Arrow Antenna makes one > for 2m. Plans are available that could possibly be scaled > to 915 MHz. Article: 217169 of rec.radio.amateur.antenna From: "Jerry Martes" References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <1126707001_31799@spool6-east.superfeed.net> Subject: Re: Open Stub fed J antenna Message-ID: Date: Wed, 14 Sep 2005 23:03:57 GMT Dave Have you considered making a coaxial version of the J-pole? http://www.ansoft.com/news/articles/04.05_MWJ.pdf Jerry "David" wrote in message news:Oh1We.47455$FA3.23606@news-server.bigpond.net.au... > Cecil, > > Thanks for the info. The open stub J looks like it should be suitable for > my application being ground independent, omni directional and having low > radiation angle. > > Cecil Moore wrote: > >> David wrote: >> >>> Does anyone know of where I could find an example of a homebrew open >>> stub >>> fed j antenna. I want to construct a unit for 915 MHz using SMA plug and >>> coaxial cable. >> >> >> An open stub J-pole is the same as a Zepp. 1/2WL element >> end fed by 1/4WL balanced series section. The coax connects >> to the end of the series section. Arrow Antenna makes one >> for 2m. Plans are available that could possibly be scaled >> to 915 MHz. Article: 217170 of rec.radio.amateur.antenna Subject: Re: 73 Ohms, How do you get it? From: Cecil Moore Date: Wed, 14 Sep 2005 18:12:26 -0500 Message-ID: <1126739706_405@spool6-east.superfeed.net> References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126653287_28145@spool6-east.superfeed.net> <1126731751.254078.115460@g49g2000cwa.googlegroups.com> Harry wrote: > Would you please explain the difference between these > two formulas (4-37 and 4-93)? Equation 4-37 is from section "4.3 SMALL DIPOLE", i.e. shorter than 1/2WL. The dipole is so short that its current distribution is triangular, not sinusoidal. Quoting section 4.3: "The radiation resistance of the antenna is strongly dependent upon the current distribution." The "1/2" on the diagram does NOT mean 1/2WL. Equation 4-93 is from section "4.6 HALF-WAVELENGTH DIPOLE". The current distribution on the thin-wire 1/2WL dipole is considered to be sinusoidal. See Figure 4.8. Note the triangular current distribution for L = 1/4WL and the sinusoidal current distribution for L = 1/2WL. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- Article: 217171 of rec.radio.amateur.antenna Subject: Re: Open Stub fed J antenna From: Cecil Moore Date: Wed, 14 Sep 2005 18:13:24 -0500 Message-ID: <1126739764_407@spool6-east.superfeed.net> References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <1126707001_31799@spool6-east.superfeed.net> David wrote: > Thanks for the info. The open stub J looks like it should be suitable > for my application being ground independent, omni directional and having > low radiation angle. Be sure to include a choking function at the feedpoint. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- Article: 217172 of rec.radio.amateur.antenna From: David Subject: Re: Open Stub fed J antenna References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <1126707001_31799@spool6-east.superfeed.net> <1126739764_407@spool6-east.superfeed.net> Message-ID: Date: Thu, 15 Sep 2005 00:34:51 GMT Thanks for the feedback everyone. The article Jerry pointed me to starts looking like the commercial antenna I was initially studying. Their unit though only had a 1/4 wave above the coaxial sleeve. From the SMA plug, the coax coiled around the radome must have been the choke to help reduce RF currents radiating from the earth braid. Then the 1/4 wave length coax forms the match followed by the expose radiating section. It looks like an open stub fed J-pole where the stub is enclosing the inner element rather than being constructed as a rod next to it. Does this seem reasonable ? (PS. I'm a beginner with regards to antenna theory and would like to understand what is happening so that I can experiment with some kind degree of success). Cecil Moore wrote: > David wrote: > >> Thanks for the info. The open stub J looks like it should be suitable >> for my application being ground independent, omni directional and >> having low radiation angle. > > > Be sure to include a choking function at the feedpoint. Article: 217173 of rec.radio.amateur.antenna From: "Jerry" References: <1126505259.234971.15970@f14g2000cwb.googlegroups.com> Subject: Re: best HF antenna system next to a trailer? Message-ID: <2K3We.5007$%Q1.3074@bignews3.bellsouth.net> Date: Wed, 14 Sep 2005 21:03:40 -0400 wrote in message news:1126505259.234971.15970@f14g2000cwb.googlegroups.com... > Hi, > > I'd like some advice for determining the best antenna to put up in my > situation. > > I am getting set to move to a trailer park in northeast arizona, about > 50 miles west of Gallup, NM. Locals have no objection to antennas so > long as people don't have to run into them via normal passage ways. > The trailer is 12 feet high by 15 feet wide by 50 feet long, facing > N-S. Nearest certain ground is electrical panel. The water pipe is > metal but could be interrupted throughout system by PVC. There may > also be significant noise from AC systems in park. > > Good news is that my wife is giving me an entire walk-in closet for my > station, and that I can lay aluminum foil against all surfaces to > create a Faraday cage. > > I have approx 25 to 30 feet between my trailer and neighbors, and a 35 > foot altitude streetlamp 6 feet away curb. Soil conductivity is red > clay, extremely poor. Significant rainfall (monsoons) summer to fall. > Winds gusting to 50 or 60 mph during winter. Soil frosts between > October to March. > > I would like to work CW DX on 40, 30, 20, and 17 meters. 80 and 160 > would > be a bonus. Conventional options such as tower or surplus telephone > pole are out of the question due to cost and lack of available area. > Radials must be buried as children are playing nearby. > > Probable options: > > 1) Load up the streetlamp with an antenna matcher, work against 180 > degrees of buried radials out to 1/8 lambda. > > 2) Solder a series of tin/steel cans (cantenna) using pocket torch and > copper tape to 1/4 lambda with added capacitance hat(s), brace the cans > against the ground and the trailer, work against 270 to 360 degrees of > buried radials out to 3/8 lambda. > > 3) Create a mast from 40 feet of metal pipe and 15 feet of wood rod, > brace against trailer burying pipe end 10 feet, mount an inverted vee > trap dipole in N-S direction for E-W DX. > > 4) Pair of masts on either side of the trailer, mount a delta loop > from each mast, feed one loop and use the other as a reflector. > > 5) Pair of cantennas on each side of the trailer, operating as out of > phase pair of 1/4 lambda verticals. > > Which would be best? And where do I place the lightning arrestor(s)? > > Thanks, > > The Eternal Squire How about the screwdriver antenna. This is compact, can even be "disguised" inside a PVC pipe, can be positioned vertically OR horizontally and can be used to tune a random wire strung into a nearby tree. I used this system on a motor home where we positioned the antenna on the rear ladder with a swivel mount. When traveling, the antenna was positioned at a 45 degree angle and rested in a wooden cradle on top of the bus. At rest, the antenna could be raised to the vertical in a minute or two and tightened with thumbscrews. Because the motor home was mostly fiberglass, we quickly discovered that the antenna could be used in the semi-horizontal position while going down the road with good results! In your case, your trailer would be a "mobile", but you could set it up in several ways to take advantage of various situations, and, also tune a random wire with it. I've done this while on field exercizes with CAP. Now I know I am partial since I make screwdrivers, but you can find a variety of makers on the web. Just try to avoid the ones made of PVC and, of course, there are those that are SUPER expensive. Go for the ones with larger diameter coils and wire sizes and avoid the ones that promise 160 thru 10. Those that promise 160 thru 10 are the ones that are wound on small diameter forms and are wound with 20 gauge wire CLOSELY together (in effect, transformer-wound) which destroys your "Q". I doubt seriously such an antenna would do much "punkin" on 160! Every body runs into compromises at times, so you have to be do the best you can do with what you have to work with. If you have 75 feet of room over your lot, then you might visit www.k1jek.com for an all-band dipole 80-10 Meters. I'm told this is a good choice for short lots. Hope this helps 73 Jerry K4KWH www.qsl.net/k4kwh > Article: 217174 of rec.radio.amateur.antenna From: dplatt@radagast.org (Dave Platt) Subject: Re: Open Stub fed J antenna Date: Thu, 15 Sep 2005 01:09:00 -0000 Message-ID: <11ihidcala4s727@corp.supernews.com> References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <1126739764_407@spool6-east.superfeed.net> In article , David wrote: >The article Jerry pointed me to starts looking like the commercial >antenna I was initially studying. Their unit though only had a 1/4 wave >above the coaxial sleeve. > > From the SMA plug, the coax coiled around the radome must have been the >choke to help reduce RF currents radiating from the earth braid. >Then the 1/4 wave length coax forms the match followed by the expose >radiating section. > >It looks like an open stub fed J-pole where the stub is enclosing the >inner element rather than being constructed as a rod next to it. > >Does this seem reasonable ? (PS. I'm a beginner with regards to antenna >theory and would like to understand what is happening so that I can >experiment with some kind degree of success). Yes, it does. Take a look at the following: http://download.antennex.com/hws/ws1002/sperrtof.pdf A Sperrtof, in effect, is a J-pole whose matching section is a coaxial tube rather than a single rod or wire. It sounds rather like what you're describing. As with all such (I think), the radiating section is 1/2 wavelength long, give or take a smidge, and behaves as an end-fed 1/2-wave dipole. The matching section isn't supposed to radiate significantly. The overall radiation pattern would, I expect, be essentially the same as other J-poles and other end-fed 1/2-wave radiators - similar to a center-fed 1/2-wave dipole, but tilted a bit "upwards" away from the feedpoint. You can distinguish a Sperrtof-type antenna from one of the coaxial dipoles Jerry referred you to, by the length of the single-wire radiator - it's 1/2-wave for a Sperrtof and 1/4-wave for a coaxial dipole (which is really a center-fed dipole). There's an interesting dual-band 2m/440 antenna which was written up in QST in October 2000 - ARRL members can get the article at http://www.arrl.org/members-only/tis/info/pdf/0010050.pdf It's interesting because it's _called_ a J-pole, _looks_ like a J-pole... but electrically it isn't. It's actually a center-fed vertical, not a Zepp. The stub at the bottom acts as a choke/decoupler, not as an impedance transformer. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! Article: 217175 of rec.radio.amateur.antenna From: David Subject: Re: Open Stub fed J antenna References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <1126739764_407@spool6-east.superfeed.net> <11ihidcala4s727@corp.supernews.com> Message-ID: Date: Thu, 15 Sep 2005 01:41:06 GMT Dave, If I scale that up to 915MHz, the dimensions are almost perfect for using RG58 coax instead of the copper tubing.The outer tube would be 5.5mm and inner conductor 1.6mm. Being 50 Ohm coax, I assume therefore I do not need to slide the tap point up as their design did. I suppose I should also add the choke coil at the antenna base for additional isolation of ground currents. The article mentions the top part as 1/2 wave and bottom at 1/4 wave. If the bottom part of their design is 505mm then the antenna must be used for 2m band. If this is the case, how come the radiating element is 1480 long ? The Coaxial antenna mentioned in the article mentioned by Jerry looks good. The version they mention with a GAP would be simple to construct. It is a 1/4 wave radiating element at the top (earth braid stripped back), then 1/4 wave of full coax, then a "small" gap, then the transmission line. They do not mention the size of the gap but I assume any small gap has the same effect of isolating the reverse current ? Should the actual lengths of these sections be modified by "K" depending on diameter of conductor or are they exact 1/4 wave length cuts ? Thanks heaps. Dave Platt wrote: > In article , > David wrote: > > >>The article Jerry pointed me to starts looking like the commercial >>antenna I was initially studying. Their unit though only had a 1/4 wave >>above the coaxial sleeve. >> >>From the SMA plug, the coax coiled around the radome must have been the >>choke to help reduce RF currents radiating from the earth braid. >>Then the 1/4 wave length coax forms the match followed by the expose >>radiating section. >> >>It looks like an open stub fed J-pole where the stub is enclosing the >>inner element rather than being constructed as a rod next to it. >> >>Does this seem reasonable ? (PS. I'm a beginner with regards to antenna >>theory and would like to understand what is happening so that I can >>experiment with some kind degree of success). > > > Yes, it does. Take a look at the following: > > http://download.antennex.com/hws/ws1002/sperrtof.pdf > > A Sperrtof, in effect, is a J-pole whose matching section is a coaxial > tube rather than a single rod or wire. It sounds rather like what > you're describing. > > As with all such (I think), the radiating section is 1/2 wavelength > long, give or take a smidge, and behaves as an end-fed 1/2-wave > dipole. The matching section isn't supposed to radiate significantly. > > The overall radiation pattern would, I expect, be essentially the same > as other J-poles and other end-fed 1/2-wave radiators - similar to a > center-fed 1/2-wave dipole, but tilted a bit "upwards" away from the > feedpoint. > > You can distinguish a Sperrtof-type antenna from one of the coaxial > dipoles Jerry referred you to, by the length of the single-wire > radiator - it's 1/2-wave for a Sperrtof and 1/4-wave for a coaxial > dipole (which is really a center-fed dipole). > > There's an interesting dual-band 2m/440 antenna which was written up > in QST in October 2000 - ARRL members can get the article at > http://www.arrl.org/members-only/tis/info/pdf/0010050.pdf > > It's interesting because it's _called_ a J-pole, _looks_ like a > J-pole... but electrically it isn't. It's actually a center-fed > vertical, not a Zepp. The stub at the bottom acts as a > choke/decoupler, not as an impedance transformer. > Article: 217176 of rec.radio.amateur.antenna Subject: Re: Open Stub fed J antenna From: Cecil Moore Date: Wed, 14 Sep 2005 21:10:14 -0500 Message-ID: <1126750373_543@spool6-east.superfeed.net> References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <1126739764_407@spool6-east.superfeed.net> <11ihidcala4s727@corp.supernews.com> David wrote: > If I scale that up to 915MHz, the dimensions are almost perfect for > using RG58 coax ... I wouldn't use RG58 for anything above HF. It has 20 dB matched line loss per 100 ft at that frequency. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- Article: 217177 of rec.radio.amateur.antenna From: David Subject: Re: Open Stub fed J antenna References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <1126739764_407@spool6-east.superfeed.net> <11ihidcala4s727@corp.supernews.com> <1126750373_543@spool6-east.superfeed.net> Message-ID: <4b5We.47625$FA3.35929@news-server.bigpond.net.au> Date: Thu, 15 Sep 2005 02:41:04 GMT So for the 1/4 wave (81mm) section of the antenna the loss would be about 0.05dB ? at 915 MHz. I typically have between 150mm (When antenna mounted on enclosure) and 2m length (when antenna external to enclosure) cable between transmitter and Antenna. (Around 1.2dB max. loss in coax between transmitter and antenna). Would this usually be acceptable or do you aim for much lower loss in the transmission line ? Max. power is 1 Watt. Most of the transceivers I play around with are around 10mW. Thanks Cecil Moore wrote: > David wrote: > >> If I scale that up to 915MHz, the dimensions are almost perfect for >> using RG58 coax ... > > > I wouldn't use RG58 for anything above HF. It has 20 dB > matched line loss per 100 ft at that frequency. Article: 217178 of rec.radio.amateur.antenna From: "Dale Parfitt" References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <1126739764_407@spool6-east.superfeed.net> <11ihidcala4s727@corp.supernews.com> <1126750373_543@spool6-east.superfeed.net> <4b5We.47625$FA3.35929@news-server.bigpond.net.au> Subject: Re: Open Stub fed J antenna Message-ID: Date: Thu, 15 Sep 2005 12:42:48 GMT "David" wrote in message news:4b5We.47625$FA3.35929@news-server.bigpond.net.au... > So for the 1/4 wave (81mm) section of the antenna the loss would be about > 0.05dB ? at 915 MHz. > 20dB/100' MATCHED line loss. W4OP Article: 217179 of rec.radio.amateur.antenna Subject: Re: Open Stub fed J antenna From: Cecil Moore Date: Thu, 15 Sep 2005 08:07:35 -0500 Message-ID: <1126789815_959@spool6-east.superfeed.net> References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <1126739764_407@spool6-east.superfeed.net> <11ihidcala4s727@corp.supernews.com> <1126750373_543@spool6-east.superfeed.net> <4b5We.47625$FA3.35929@news-server.bigpond.net.au> David wrote: > So for the 1/4 wave (81mm) section of the antenna the loss would be > about 0.05dB ? at 915 MHz. Depends upon whether you leave the insulation on the radiating part or not. But what I was concerned about is the transmission line. You lose about half of your power every 15 feet. Until your last posting, you didn't tell us the length of the transmission line but personally I find 1.2 dB matched line loss in six feet to be unacceptable. Any SWR above 1:1 and the losses are even greater. > Cecil Moore wrote: >> I wouldn't use RG58 for anything above HF. It has 20 dB >> matched line loss per 100 ft at that frequency. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Article: 217180 of rec.radio.amateur.antenna From: "Fred W4JLE" References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Date: Thu, 15 Sep 2005 10:41:17 -0400 Message-ID: While I would agree with officious and petty, moron and bigot do not apply >from my readings. I get really tired of that old saw being hauled out and applied to people; simply because others disagree with their actions. A few moments spent perusing a dictionary will show that simply refusing to take in a storm victim, while abhorrent to me, does not make one a bigot. "Michael A. Terrell" wrote in message news:4324E0BD.A033E1A@earthlink.net... > "LenAnderson@ieee.org" wrote: > > > > The disaster of hurricane Katrina is of unparalleled proportions > > and ALL humane-thinking citizens can do their part, however big, > > however small. > > > And then, there are the morons and bigots: > > > > -- > ? > > Michael A. Terrell > Central Florida Article: 217181 of rec.radio.amateur.antenna From: "Fred W4JLE" References: <1126505259.234971.15970@f14g2000cwb.googlegroups.com> <9175-4326EEA5-1@storefull-3254.bay.webtv.net> <1126670383.884527.133320@f14g2000cwb.googlegroups.com> Subject: Re: best HF antenna system next to a trailer? Date: Thu, 15 Sep 2005 10:56:26 -0400 Message-ID: <71e25$43298bb2$471c610a$29323@ALLTEL.NET> Smack her in the head and put up a tower, It has worked on all 7 of my wives. :>) wrote in message news:1126670383.884527.133320@f14g2000cwb.googlegroups.com... > Money and space are actually limiting factors, but at least CC&R's > arent! My wife and I have been discussing this, and she really > doesn't like the idea of something 30 to 40 feet high on a small lot. > > Her interest actually is gardening and we had been discussing > containing an area of decent topsoil within a square formed by railroad > ties. She has no objection to 20 to 25 foot high metal poles on the > corners of a square 20 to 25 foot on the side... which turns out to be > the core geometry of a 20 meter 4-square broadside phase array. > > I would lay the poles first in concrete reinforced holes, connect the > feed network and radials on the dirt, and lay feed line underground > from the array to just near the trailer. Then I would lay the railroad > ties along the square, and then fill the square with topsoil. > > Additional radials would need to be buried under a couple inches of red > clay fanning out from the square. > > Variations: > 1) could I create trap verticals from the poles for 20, 17, 15, and 10 > meters, or do I need inscribed squares of seperate verticals because > seperate phased feeds might be needed for these other bands? > 2) could I simply operate the square outside of 20 meters with a tuner > for local operation? > > I think because space, money, and aesthetics are limiting factors, I > need to use precision to my advantage rather than size or height, and a > 4 square may help there. > > Comments? > > The Eternal Squire > Article: 217182 of rec.radio.amateur.antenna From: "Caveat Lector" Subject: Katrina Ham Stories Message-ID: Date: Thu, 15 Sep 2005 08:20:00 -0700 http://ac6v.com/new.htm See big antenna in action Ham Radio Rescue Effort On TV http://easylink.playstream.com/katu/050831ham_operator_530pm.wvx -- CL -- I doubt, therefore I might be ! Article: 217183 of rec.radio.amateur.antenna From: "Fred W4JLE" References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Date: Thu, 15 Sep 2005 12:00:29 -0400 Message-ID: <31f74$43299abf$471c63c6$12083@ALLTEL.NET> Perhaps you could show me where any of the offered definitions apply to an HOA rule that prohibits non family members from residing in a home. "Richard Clark" wrote in message news:4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com... > On Thu, 15 Sep 2005 10:41:17 -0400, "Fred W4JLE" > wrote: > > >A few moments spent perusing a dictionary will show that simply refusing to > >take in a storm victim, while abhorrent to me, does not make one a bigot. > > > from the Oxford English Dictionary: > > Bigot. 1598. 1. A hypocrite. 2. A superstitious person - 1664. 3. A > person obstinately and unreasonably wedded to a creed, opinion or > ritual - 1661. Intolerant toward others - 1645. > > Hardly seems that the meaning has veered from this in the past 340 > years. > > 73's > Richard Clark, KB7QHC Article: 217184 of rec.radio.amateur.antenna From: Walter Maxwell Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Message-ID: References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> Date: Thu, 15 Sep 2005 12:01:35 -0400 In light of Colin Powell's position that the fate of the poorer people of New Orleans was not due to racism, but only failing to realize that those people had no means for transportation out of the city, it seems to me that racism and bigotry were not involved. To me it's significant that that position is held by a highly-respected person of color. Walt, W2DU On Thu, 15 Sep 2005 08:36:56 -0700, Richard Clark wrote: >On Thu, 15 Sep 2005 10:41:17 -0400, "Fred W4JLE" >wrote: > >>A few moments spent perusing a dictionary will show that simply refusing to >>take in a storm victim, while abhorrent to me, does not make one a bigot. >> >from the Oxford English Dictionary: > >Bigot. 1598. 1. A hypocrite. 2. A superstitious person - 1664. 3. A >person obstinately and unreasonably wedded to a creed, opinion or >ritual - 1661. Intolerant toward others - 1645. > >Hardly seems that the meaning has veered from this in the past 340 >years. > >73's >Richard Clark, KB7QHC Article: 217185 of rec.radio.amateur.antenna From: "John N9JG" Subject: Wooden I section pole Date: Thu, 15 Sep 2005 11:36:27 -0500 Message-ID: I am in the planning stage for a 160 meters compact loop antenna. A loop antenna may not have metal nearby, so I am planning to use a wooden pole to support the top of the loop. In the ARRL Antenna handbook, it states that "W5QJR made a pole of 2 x 4-inch lumber with 1 x 4-inch boards on either side to form an I section. He held the boards together with 1/4-inch bolts, 2 feet apart and tied rope guys to the top. This made an excellent mast up to 50 feet high." Does anyone have any comments on the feasibility of an unguyed pole using this same type of construction? Naturally, a portion of the pole would have to be underground, and perhaps set in concrete. What about a 50 feet pole, with 10 feet underground ,which would give you a 40 foot mast? An alternative would be to have a contractor install a 40 feet utility pole, but I assume the wooden pole described above would be less of an eyesore (to the neighbors) than a utility pole. Any comments and advice will be appreciated. John, N9JG Article: 217186 of rec.radio.amateur.antenna From: "Fred W4JLE" References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Date: Thu, 15 Sep 2005 12:40:44 -0400 Message-ID: Even more frustrating is the number of school buses controlled by a black Mayor that never were put in to evacuation service. The same buses now set in water and I am sure they will be replaced at taxpayers expense. As I was somewhat involved in the political debacle, I can tell you from personal experience that Red Cross and amateur radio vans were prohibited >from entering the disaster area. My cynical side says that in the background, a chance was both seen and taken to make George Bush look bad. The democrat political machine in New Orleans is only surpassed by that of Chicago. I know for a fact the Red Cross was told that if they were to feed the people in the superdome they would stay. Some how I find it ironical that a black mayor applied the same wisdom to his people that my mother applied to the neighborhood stay dog I attempted to feed. Where were all the murdered bodies, in the superdome, the press reported on so breathlessly? The must have hid them in Al Capone's vault to make Geraldo look bad; as he worked for the evil Fox network... Of course the more the race card is played, the more money is offered by white America to assuage the implied guilt. Black poloticos have learned this lesson well! "Walter Maxwell" wrote in message news:ma6ji1ta47t9n95hh87nssvc4it2pjlko1@4ax.com... > In light of Colin Powell's position that the fate of the poorer people > of New Orleans was not due to racism, but only failing to realize > that those people had no means for transportation out of the city, it > seems to me that racism and bigotry were not involved. To me it's > significant that that position is held by a highly-respected person of > color. > > Walt, W2DU Article: 217187 of rec.radio.amateur.antenna From: "David G. Nagel" Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Date: Thu, 15 Sep 2005 12:08:23 -0500 Message-ID: <11ijakdlh2ucb26@corp.supernews.com> References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> If the poor people of New Orleans didn't have transportation out of town it was because their elected Mayor refused to have them humiliated by having to leave town in a school bus or city bus. He wanted Greyhound busses with working air-conditioning for them. It's in the disaster plan to use busses for evacuation. Read it. Walter Maxwell wrote: > In light of Colin Powell's position that the fate of the poorer people > of New Orleans was not due to racism, but only failing to realize > that those people had no means for transportation out of the city, it > seems to me that racism and bigotry were not involved. To me it's > significant that that position is held by a highly-respected person of > color. > > Walt, W2DU > > > On Thu, 15 Sep 2005 08:36:56 -0700, Richard Clark > wrote: > > >>On Thu, 15 Sep 2005 10:41:17 -0400, "Fred W4JLE" >>wrote: >> >> >>>A few moments spent perusing a dictionary will show that simply refusing to >>>take in a storm victim, while abhorrent to me, does not make one a bigot. >>> > >>from the Oxford English Dictionary: > >>Bigot. 1598. 1. A hypocrite. 2. A superstitious person - 1664. 3. A >>person obstinately and unreasonably wedded to a creed, opinion or >>ritual - 1661. Intolerant toward others - 1645. >> >>Hardly seems that the meaning has veered from this in the past 340 >>years. >> >>73's >>Richard Clark, KB7QHC > > Article: 217188 of rec.radio.amateur.antenna Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article From: Cecil Moore Date: Thu, 15 Sep 2005 12:29:47 -0500 Message-ID: <1126805610_1361@spool6-east.superfeed.net> References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> <11ijakdlh2ucb26@corp.supernews.com> David G. Nagel wrote: > It's in the disaster plan to use busses for evacuation. One news service reported that billions earmarked for mass transit and levee improvements had been spent on advertising for the tourism industry. -- 73, Cecil, http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- Article: 217189 of rec.radio.amateur.antenna From: "Reg Edwards" Subject: Re: Wooden I section pole Date: Thu, 15 Sep 2005 18:05:36 +0000 (UTC) Message-ID: References: A vertical conductor, a metal tube, running diametrically across a large magloop with the tuning capacitor at the top, has no effect either on radiating efficiency or the radiation pattern. It may as well not be there apart from providing a prop or support for the antenna itself. It will, of course, need to be well-insulated from the high-voltage parts. In general, provided the longest dimension of foreign metalwork is much less than 1/2-wavelength, and there is not much of it, negligible loss will be induced in it. This is due to the very low loss resistance of most metals. Metalwork in the vicinity of beam antennas may upset only the radiation pattern. Short lengths of foreign metalwork in close vicinity of tramsmission lines, such as open-wire and ladder lines, will cause neglible loss but will slightly reduce the line impedance Zo which might affect the L and C settings of the tuner. But beware of "semi-conductors", like damp wood such as foliage and tree trunks, in the near-fields of antennas and lines. Their higher impedance provide a better power match to the 'generator'. You can have as much foreign polyethylene as you like. ---- Reg. Article: 217190 of rec.radio.amateur.antenna From: "news-z-non-exist-z" Subject: Re: 73 Ohms, How do you get it? Date: Thu, 15 Sep 2005 21:26:04 +0300 Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> <11iesohk2gnkf80@corp.supernews.com> | "Roy Lewallen" | wrote in message news:11iesohk2gnkf80@corp.supernews.com... | | Just about any antenna textbook will show you the calculation | [...] | ln(gamma * x) - (x^2)/(2!2) + (x^4)/(4!4) - (x^6)/(6!6). . . | | Roy Lewallen, W7EL [... ] and after all that, we finally draw a figure such the one at: http://antennas.ee.duth.gr/Antennas_Notes_II_2005/23.htm pezSV7BAXdag Article: 217191 of rec.radio.amateur.antenna From: dplatt@radagast.org (Dave Platt) Subject: Re: Open Stub fed J antenna Date: Thu, 15 Sep 2005 18:37:48 -0000 Message-ID: <11ijfrs1plk1a5c@corp.supernews.com> References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <11ihidcala4s727@corp.supernews.com> In article , David wrote: >Dave, > >If I scale that up to 915MHz, the dimensions are almost perfect for >using RG58 coax instead of the copper tubing.The outer tube would be >5.5mm and inner conductor 1.6mm. Being 50 Ohm coax, I assume therefore I >do not need to slide the tap point up as their design did. Bad assumption, I think. The portion of the matching section between the tap point and the bottom is a shorted stub, which adds some inductive reactance at the feedpoint. If you don't have it, you won't get a good match. Another approach I've seen to creating the necessary shorted stub is to just use RG-58 and a simple BNC "T" connector. If you look at the Sperrtopf antenna design, picture it made this way: - one long piece of RG-58 1380 mm long, with the upper part of the outer shield removed... that's your radiator, and the portion of the matching section above the feedpoint. - A second section of RG-58, about 100 mm long, with one end shorted. That's the stub. - The feedline RG-58. Now, just connect all three together... radiator/matching section, stub, and feedline. You can solder 'em, or add BNC plugs and use a BNC "T". If you do the latter, remember to include the lengths of the plugs and "T" into account. > I suppose I >should also add the choke coil at the antenna base for additional >isolation of ground currents. Certainly would not hurt to do so. You could either coil the coax below the bottom of the matching section, or add a quarter-wave choke sleeve, or just run the coax through a few ferrite beads. >The article mentions the top part as 1/2 wave and bottom at 1/4 wave. If >the bottom part of their design is 505mm then the antenna must be used >for 2m band. If this is the case, how come the radiating element is 1480 >long ? I think there's some confusion in the antenna schematic diagram, compared with the text and parts list. The diagram appears to show the upper (radiating) portion of the center element being 1480 mm, but the parts list indicates that the *total* length of the inner element is 1480 mm. The latter seems more correct to me... it'd give you a radiating element of (1480 - 505) = 975 mm, which is a bit less than 1/2 physical wavelength at 2 meters. This seems reasonable to me given that the radiating element is fairly thick (10mm) rather than a thin wire. >The Coaxial antenna mentioned in the article mentioned by Jerry looks >good. The version they mention with a GAP would be simple to construct. >It is a 1/4 wave radiating element at the top (earth braid stripped >back), then 1/4 wave of full coax, then a "small" gap, then the >transmission line. They do not mention the size of the gap but I assume >any small gap has the same effect of isolating the reverse current ? I'm not clear about the gap configuration either. The article sort of implies that its size has to be set experimentally, so that the leakage current through the gap is the right amount to cancel out the signal propagating back down the outside of the upper section. The article doesn't say whether the gap is supposed to go around the full circumference of the coax (completely isolating the upper and lower portions of the shield) or only partially around... I infer that it's the latter, because I don't see how the antenna could work with the shield sections fully separated. >Should the actual lengths of these sections be modified by "K" depending >on diameter of conductor or are they exact 1/4 wave length cuts ? Well, I think it's a bit of a compromise. The upper section (the coax center conductor and its surrounding dielectric) is going to have a velocity factor of not much less than 1.0. Cutting to 1/4 physical wavelength, and then trimming a bit, seems likely to work. I think the lower section is likely to be a bit trickier, since there are actually two velocity factors involved. The radiating is done by the RF travelling back down the outside of the coax braid from the feedpoint, and this (like the upper section) will have a velocity factor close to 1.0, which suggests that the gap-to-feedpoint distance should be close to 1/4 physical wavelength. HOWEVER: the signal travelling up the *inside* of the braid, like that travelling up the inner conductor towards the feedpoint, will be travelling more slowly - the velocity factor will be somewhere around .66 - .8 depending on cable type. This means that there will be more than 180 degrees of phase delay between the signal passing the gap going upwards (inside the cable) and the signal reaching the gap from above (travelling back down the outside of the cable). Hence, the gap leakage won't result in full cancellation of the signal travelling down the outside of the coax past the gap. To get the two signals into accurate 180-degree phase opposition, you'd need to make the distance from the feedpoint to the gap a bit less than 1/4 physical wavelength, but a bit more than 1/4 of the coax's usual electrical wavelength. Splitting the difference might work fairly well. I'm not sure what this will do to the antenna's feedpoint impedance / return loss, though, and it'll probably tilt the antenna's radiation pattern somewhat. You will probably need to experiment to get the best compromise between antenna pattern and feedpoint impedance / return loss / SWR. The same is true of the gap size and configuration. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! Article: 217192 of rec.radio.amateur.antenna From: "Percival P. Cassidy" Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> <31f74$43299abf$471c63c6$12083@ALLTEL.NET> Message-ID: <3gjWe.15460$tc7.10245@fe03.lga> Date: Thu, 15 Sep 2005 14:42:06 -0400 On 09/15/05 01:08 pm Richard Clark tossed the following ingredients into the ever-growing pot of cybersoup: >>Perhaps you could show me where any of the offered definitions apply to an >>HOA rule that prohibits non family members from residing in a home. > Christian charity is not fulfilled by a shrug of the HOA committee, > and members who enjoy the veil of these rules won't find it any easier > getting through the eye of the needle. Amen, Brother. "Perce" Article: 217193 of rec.radio.amateur.antenna From: Allodoxaphobia Subject: Re: 73 Ohms, How do you get it? Date: 15 Sep 2005 18:51:10 GMT Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> <11iesohk2gnkf80@corp.supernews.com> On Thu, 15 Sep 2005 21:26:04 +0300, news-z-non-exist-z wrote: >| "Roy Lewallen" >| wrote in message news:11iesohk2gnkf80@corp.supernews.com... >| >| Just about any antenna textbook will show you the calculation >| [...] >| ln(gamma * x) - (x^2)/(2!2) + (x^4)/(4!4) - (x^6)/(6!6). . . >| >| Roy Lewallen, W7EL > > [... ] and after all that, > we finally draw a figure such the one at: > > http://antennas.ee.duth.gr/Antennas_Notes_II_2005/23.htm > > pezSV7BAXdag Yes, but: http://antennas.ee.duth.gr/Antennas_Notes_II_2005/22.htm explains it best of all! HI!HI! 73 Jonesy -- Marvin L Jones | jonz | W3DHJ | linux Pueblo, Colorado | @ | Jonesy | OS/2 __ 38.24N 104.55W | config.com | DM78rf | SK Article: 217194 of rec.radio.amateur.antenna From: "Fred W4JLE" References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> <31f74$43299abf$471c63c6$12083@ALLTEL.NET> Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Date: Thu, 15 Sep 2005 14:51:11 -0400 Message-ID: <6906e$4329c2c1$471c63c6$4287@ALLTEL.NET> Weak Richard, but we love you no less. "Richard Clark" wrote in message news:t3aji1hsepkfap9c8i3h0j3t592t8nedfd@4ax.com... > On Thu, 15 Sep 2005 12:00:29 -0400, "Fred W4JLE" > wrote: > > >Perhaps you could show me where any of the offered definitions apply to an > >HOA rule that prohibits non family members from residing in a home. > > You said it yourself: > >>refusing to take in a storm victim > exactly conforms to > >>>Intolerant toward others - 1645. > > otherwise, why would you offer your opinion > >>while abhorrent to me > > Christian charity is not fulfilled by a shrug of the HOA committee, > and members who enjoy the veil of these rules won't find it any easier > getting through the eye of the needle. > > 73's > Richard Clark, KB7QHC Article: 217195 of rec.radio.amateur.antenna From: "Fred W4JLE" References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> <11ijakdlh2ucb26@corp.supernews.com> <1126805610_1361@spool6-east.superfeed.net> Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Date: Thu, 15 Sep 2005 14:53:01 -0400 Message-ID: Not to mention the purchase of a casino and the construction of a Marina. "Cecil Moore" wrote in message news:1126805610_1361@spool6-east.superfeed.net... > David G. Nagel wrote: > > It's in the disaster plan to use busses for evacuation. > > One news service reported that billions earmarked for mass > transit and levee improvements had been spent on advertising > for the tourism industry. > -- > 73, Cecil, http://www.qsl.net/w5dxp > > ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- > http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups > ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- Article: 217196 of rec.radio.amateur.antenna Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article From: Cecil Moore Date: Thu, 15 Sep 2005 13:55:56 -0500 Message-ID: <1126810780_1703@spool6-east.superfeed.net> References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> <31f74$43299abf$471c63c6$12083@ALLTEL.NET> Richard Clark wrote: > Christian charity is not fulfilled by a shrug of the HOA committee, > and members who enjoy the veil of these rules won't find it any easier > getting through the eye of the needle. The small "eye of the needle" gate at the walls of a city was sized for human beings. It was camels that couldn't get through it. Camels had to enter through the main gate. -- 73, Cecil, http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- Article: 217197 of rec.radio.amateur.antenna From: "KØHB" References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> <31f74$43299abf$471c63c6$12083@ALLTEL.NET> Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Message-ID: Date: Thu, 15 Sep 2005 19:09:05 GMT "Richard Clark" wrote > > Christian charity is not fulfilled by a shrug of the HOA committee, > and members who enjoy the veil of these rules won't find it any easier > getting through the eye of the needle. > How is "Christian charity" different from other charity, and do I need to be a member of your cult in order to get through the eye of the needle (and why would I want to?)? 73, de Hans, K0HB -- Homepage: http://www.home.earthlink.net/~k0hb Member: ARRL http://www.arrl.org SOC http://www.qsl.net/soc VWOA http://www.vwoa.org A-1 Operator Club http://www.arrl.org/awards/a1-op/ TCDXA http://www.tcdxa.org MWA http://www.w0aa.org TCFMC http://www.tcfmc.org FISTS http://www.fists.org LVDXA http://www.upstel.net/borken/lvdxa.htm NCI http://www.nocode.org Article: 217198 of rec.radio.amateur.antenna From: nospam@nouce.bellatlantic.net Subject: Re: Open Stub fed J antenna Message-ID: <9ogji11j72vmidsbque5h0utjt7mgj40b2@4ax.com> References: <6kPVe.45149$FA3.38745@news-server.bigpond.net.au> <11ihidcala4s727@corp.supernews.com> <11ijfrs1plk1a5c@corp.supernews.com> Date: Thu, 15 Sep 2005 19:13:28 GMT On Thu, 15 Sep 2005 18:37:48 -0000, dplatt@radagast.org (Dave Platt) wrote: >In article , >David wrote: > >>Dave, >> >>If I scale that up to 915MHz, the dimensions are almost perfect for >>using RG58 coax instead of the copper tubing.The outer tube would be >>5.5mm and inner conductor 1.6mm. Being 50 Ohm coax, I assume therefore I >>do not need to slide the tap point up as their design did. Using RG58 at 900mhz is a lossy situation to be avoided. >Bad assumption, I think. The portion of the matching section between >the tap point and the bottom is a shorted stub, which adds some >inductive reactance at the feedpoint. If you don't have it, you won't >get a good match. True. You can alter the lengths and use the stub section to cancel the inductive or capacitive reactance set up by the radiating element if present. If your radiating element is capacitive (tad shorter) then the stub can be open which will reflect as inductive. It's only a matter of juggling the numbers. >Another approach I've seen to creating the necessary shorted stub is >to just use RG-58 and a simple BNC "T" connector. If you look at the >Sperrtopf antenna design, picture it made this way: > >- one long piece of RG-58 1380 mm long, with the upper part of > the outer shield removed... that's your radiator, and the portion > of the matching section above the feedpoint. > >- A second section of RG-58, about 100 mm long, with one end shorted. > That's the stub. > >- The feedline RG-58. > >Now, just connect all three together... radiator/matching section, >stub, and feedline. You can solder 'em, or add BNC plugs and use a >BNC "T". If you do the latter, remember to include the lengths of the >plugs and "T" into account. > >> I suppose I >>should also add the choke coil at the antenna base for additional >>isolation of ground currents. > >Certainly would not hurt to do so. You could either coil the coax >below the bottom of the matching section, or add a quarter-wave choke >sleeve, or just run the coax through a few ferrite beads. If the antenna feed point is a matched condition what is the RF on the coax shield from? It should be very small. >>The article mentions the top part as 1/2 wave and bottom at 1/4 wave. If >>the bottom part of their design is 505mm then the antenna must be used >>for 2m band. If this is the case, how come the radiating element is 1480 >>long ? > >I think there's some confusion in the antenna schematic diagram, >compared with the text and parts list. The diagram appears to show >the upper (radiating) portion of the center element being 1480 mm, but >the parts list indicates that the *total* length of the inner element >is 1480 mm. For 2m the correct length for the total center element is 1480 (58"). At 2m the halfwave length is in free space is 1M or for real elements about 38" (.95M) or a K around .96-97. >The latter seems more correct to me... it'd give you a radiating >element of (1480 - 505) = 975 mm, which is a bit less than 1/2 >physical wavelength at 2 meters. This seems reasonable to me given >that the radiating element is fairly thick (10mm) rather than a thin >wire. Correct. Thick elements do make a noticeable difference especially when the ratio of wavelength to element diameter gets below 500:1. The effect is elements are shorter, bandwidth wider. >>The Coaxial antenna mentioned in the article mentioned by Jerry looks >>good. The version they mention with a GAP would be simple to construct. >>It is a 1/4 wave radiating element at the top (earth braid stripped >>back), then 1/4 wave of full coax, then a "small" gap, then the >>transmission line. They do not mention the size of the gap but I assume >>any small gap has the same effect of isolating the reverse current ? There is no requirement for the bottom to be coaxial. it can be parallel lines (convential Jpole) in either case the antenna is a 1/2 lamda using a open section of transmission line for matching. >I'm not clear about the gap configuration either. The article sort of >implies that its size has to be set experimentally, so that the >leakage current through the gap is the right amount to cancel out the >signal propagating back down the outside of the upper section. The >article doesn't say whether the gap is supposed to go around the full >circumference of the coax (completely isolating the upper and lower >portions of the shield) or only partially around... I infer that it's >the latter, because I don't see how the antenna could work with the >shield sections fully separated. The gap is fully open. Also that gap sets up a transmisstion line between the outer braid and the inner transmission line braid. There is an interaction between the gap and braid section length. >>Should the actual lengths of these sections be modified by "K" depending >>on diameter of conductor or are they exact 1/4 wave length cuts ? Yes. however the difference between K and free space will be maybe a 2-4% difference. At 2m that comes out to around .5" (12mm) give or take. >Well, I think it's a bit of a compromise. > >The upper section (the coax center conductor and its surrounding >dielectric) is going to have a velocity factor of not much less than >1.0. Cutting to 1/4 physical wavelength, and then trimming a bit, >seems likely to work. Even without insulation it's lower than 1.0 (likely .98 or so) but insulation will increase that. >I think the lower section is likely to be a bit trickier, since >there are actually two velocity factors involved. The radiating is >done by the RF travelling back down the outside of the coax braid from >the feedpoint, and this (like the upper section) will have a velocity >factor close to 1.0, which suggests that the gap-to-feedpoint distance >should be close to 1/4 physical wavelength. > >HOWEVER: the signal travelling up the *inside* of the braid, like that >travelling up the inner conductor towards the feedpoint, will be >travelling more slowly - the velocity factor will be somewhere around >.66 - .8 depending on cable type. This means that there will be more >than 180 degrees of phase delay between the signal passing the gap >going upwards (inside the cable) and the signal reaching the gap from >above (travelling back down the outside of the cable). Hence, the gap >leakage won't result in full cancellation of the signal travelling >down the outside of the coax past the gap. > >To get the two signals into accurate 180-degree phase opposition, >you'd need to make the distance from the feedpoint to the gap a bit >less than 1/4 physical wavelength, but a bit more than 1/4 of the >coax's usual electrical wavelength. Splitting the difference might >work fairly well. > >I'm not sure what this will do to the antenna's feedpoint impedance / >return loss, though, and it'll probably tilt the antenna's radiation >pattern somewhat. You will probably need to experiment to get the >best compromise between antenna pattern and feedpoint impedance / >return loss / SWR. The same is true of the gap size and configuration. If properly matched the feedpoint will be 50ohms and the return loss will be reflective of a good match. Allison Kb1GMX Article: 217199 of rec.radio.amateur.antenna From: "John N9JG" Subject: Re: Wooden I section pole Date: Thu, 15 Sep 2005 14:44:19 -0500 Message-ID: References: This is useful information to know. I don't know why the section about small loops in the Antenna Handbook doesn't mention this. BTW, how far does the near-field extend? "Reg Edwards" wrote in message news:dgcd5g$j7b$1@nwrdmz01.dmz.ncs.ea.ibs-infra.bt.com... >A vertical conductor, a metal tube, running diametrically across a > large magloop with the tuning capacitor at the top, has no effect > either on radiating efficiency or the radiation pattern. It may as > well not be there apart from providing a prop or support for the > antenna itself. It will, of course, need to be well-insulated from the > high-voltage parts. > > In general, provided the longest dimension of foreign metalwork is > much less than 1/2-wavelength, and there is not much of it, negligible > loss will be induced in it. This is due to the very low loss > resistance of most metals. > > Metalwork in the vicinity of beam antennas may upset only the > radiation pattern. > > Short lengths of foreign metalwork in close vicinity of tramsmission > lines, such as open-wire and ladder lines, will cause neglible loss > but will slightly reduce the line impedance Zo which might affect the > L and C settings of the tuner. > > But beware of "semi-conductors", like damp wood such as foliage and > tree trunks, in the near-fields of antennas and lines. Their higher > impedance provide a better power match to the 'generator'. > > You can have as much foreign polyethylene as you like. > ---- > Reg. > > Article: 217201 of rec.radio.amateur.antenna From: "news-z-non-exist-z" Subject: Re: 73 Ohms, How do you get it? Date: Thu, 15 Sep 2005 23:04:17 +0300 Message-ID: References: <1126625499.680151.37850@g47g2000cwa.googlegroups.com> <1126638695.918035.51910@z14g2000cwz.googlegroups.com> <11iesohk2gnkf80@corp.supernews.com> "Allodoxaphobia" wrote in message news:slrndijgku.1fdu.bit-bucket@shell.config.com... | On Thu, 15 Sep 2005 21:26:04 +0300, news-z-non-exist-z wrote: | [...] | Yes, but: | http://antennas.ee.duth.gr/Antennas_Notes_II_2005/22.htm | | explains it best of all! HI!HI! | | 73 | Jonesy d;^) Article: 217202 of rec.radio.amateur.antenna From: "KØHB" References: <11htogetcauugb1@news.supernews.com> <1126247960.516709.218910@g49g2000cwa.googlegroups.com> <1126296865.329405.72430@g43g2000cwa.googlegroups.com> <4324E0BD.A033E1A@earthlink.net> <4o4ji1p26o2mcctbkfbuugpan1qmlt05nd@4ax.com> <31f74$43299abf$471c63c6$12083@ALLTEL.NET> <1126813628_2069@spool6-east.superfeed.net> Subject: Re: "Hams to the Rescue After Katrina" MSNBC News Article Message-ID: Date: Thu, 15 Sep 2005 20:33:13 GMT "Cecil Moore" wrote > > Hans, Richard has obviously followed Christian principles by > selling all that he owns, giving the proceeds to the poor, > and becoming a pennyless missionary. But wait, he appears not > to have sold his computer yet. :-) > -- > 73, Cecil, http://www.qsl.net/w5dxp > Cecil, you are one dangerous dude! Welcome back. I misse