Article: 223986 of rec.radio.amateur.antenna From: "Jeff" Subject: Re: Insulation diameter vs Impedance OR how to get 20dBi out of a short Dipole Date: Mon, 1 May 2006 09:10:06 +0100 Message-ID: References: >However, I > found I could reduce the size of a 40M antenna to nearly half by > surrounding the entire radiator with a water jacket only 40cM thick. > It has a good match, and loses roughly a quarter dB to the full size > antenna. It remains to be seen if this is just another aberration, or > is an actual solution. > > 73's > Richard Clark, KB7QHC Surely it is your model that is an aberration. Did it include such things as the loss tangent of the dielectric and the effects of the resistivity of the liquid ? Di-electric loading is a valid concept, but it has to be done sensibly, and modelled even more carefully, taking ALL the effects of the di-electric into account. GIGO. Regards Jeff Article: 223987 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Insulation diameter vs Impedance OR how to get 20dBi out of a Date: Mon, 01 May 2006 02:30:17 -0700 Message-ID: <125bl9gg0e9hu64@corp.supernews.com> References: Jeff wrote: > > Surely it is your model that is an aberration. Did it include such things as > the loss tangent of the dielectric and the effects of the resistivity of the > liquid ? > > Di-electric loading is a valid concept, but it has to be done sensibly, and > modelled even more carefully, taking ALL the effects of the di-electric into > account. GIGO. The flaw is that the "wire insulation" feature of EZNEC is valid only for thin coatings, such as those typically found on insulated wire. I suspect it may also be invalid also for extreme values of dielectric constant. I don't at present know exactly at what thickness or dielectric constant the calculation becomes invalid, so results from models with exceptionally thick and/or high dielectric insulation should be viewed with some skepticism. These limitations aren't spelled out in the EZNEC manual, an oversight on my part for which I apologize. They will be included in the next update to the manual, which will probably be included with the next program update (v. 4.0.27). Roy Lewallen, W7EL Article: 223988 of rec.radio.amateur.antenna From: "Yuri Blanarovich" References: <1146380239.089435.216750@j33g2000cwa.googlegroups.com> <9731-44552433-56@storefull-3254.bay.webtv.net> <1146481819.035769.4590@y43g2000cwc.googlegroups.com> Subject: Re: Velocity Factor and resonant frequency Message-ID: Date: Mon, 1 May 2006 08:48:11 -0400 There you go again. What applies to you , you are trying to slap on others. Reputation is judged by others, judging our doings and record. How is your statement "JI Engineering" made in public and publications justified? I will not go into listing my accomplishments and professional background like Richard did (it would be another big egg on your pea brain and big mouth), I don't make living of ham radio and I don't care what you think. Fair warning back to you! You starting to sound like Freaktenna, nice going! 73 Yuri wrote in message news:1146481819.035769.4590@y43g2000cwc.googlegroups.com... > Yuri, > > Just a fair warning. > > I'd be very careful what you say in public. > At some point your big mouth and very small brain will get you into > trouble. > > Do not be too bold with your personal comments when you do not know > what you are saying and your statements are full of errors. False > statements if they cause harm will backfire on you, I can promise that. > > On a similar topic, don't blame others for your lack of self-esteem. > When you are and how you feel about yourself isn't anyone's problem but > you own. You make your own reputation Yuri. Please don't try to make > me look as bad as you. > > Tom > Article: 223989 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: A little more on missing degrees References: Message-ID: Date: Mon, 01 May 2006 13:30:05 GMT Reg Edwards wrote: > For those of you who may be unfamiliar with the mathematics of > transmission lines, download program TWOLINES and enter the following > practical values - > > Line-1 represents the loading coil. > Line-2 represents the whip to be pruned for 1/4-wave resonance. > > Enter Zo1 = 6000 ohms, a practical value. > Enter electrical length L1 = 0.15 wavelengths. > Enter attenuation = 0.1 dB for wire loss in coil. Ignoring losses and starting at 0-j0, plotting this value on a Smith Chart normalized to 6000 ohms, the normalized value is -j1.38 -j1.38 * 6000 = -j8280 ohms > Enter Zo2 = 400 ohms, a practical value. > Enter electrical length L2 = 0.0077 wavelengths. > Enter attenuation = 0.001 dB Starting at 0-j*infinity and plotting backwards, this value on a Smith Chart normalized to 400 ohms is -j20.7 -j20.7 * 400 = -j8280 ohms > But L1 + L2 = 0.1577 wavelengths = only 57 degrees. The abrupt jump from -j1.38 to -j20.7 provides a 66 degree phase shift in the angle of the reflection coefficient as read off the Smith Chart. > The missing 90 - 57 = 33 degrees are just not needed for resonance. > So why is everybody making such a fuss about it? The missing 33 degrees are there, provided by the phase shift in the reflection coefficient. The angle of the reflection coefficient in the stinger at the impedance discontinuity is ~6 degrees. The angle of the reflection coefficient in the coil at the impedance discontinuity is ~72 degrees. 72 - 6 = a 66 degree jump in the angle of the reflection coefficient. That equates to the missing 33 degrees of antenna. The wave that is only 3 degrees back from the tip reflection point is suddenly only 54 degrees from the current maximum point. It appears to me that the interference of the forward and reflected waves at the impedance discontinuity causes an actual 33 degree phase shift. How to analyze what happens at such an impedance discontinuity is covered in my energy analysis article at: http://www.qsl.net/w5dxp/energy.htm I will try to do that analysis sometime today. -- 73, Cecil http://www.qsl.net/w5dxp Article: 223990 of rec.radio.amateur.antenna From: "Richard Fry" References: Subject: Re: A little more on missing degrees Date: Mon, 1 May 2006 08:31:00 -0500 Message-ID: <44560cd1_2@newsfeed.slurp.net> "Reg Edwards" > The missing 90 - 57 = 33 degrees are just not needed for > resonance. So why is everybody making such a fuss about it? _____________ An antenna * system * does not need to have X number of degrees to be resonant. It only needs to have ~zero reactance at its feedpoint -- which, for electrically short AND long radiators can be achieved by use of a suitable matching network. Such networks don't add or subtract electrical degrees, however. They only reduce/cancel the natural reactance of the physical radiator in use. RF Article: 223991 of rec.radio.amateur.antenna From: "Dale Parfitt" References: Subject: Re: Plastic Antenna Insulators Message-ID: <1Vo5g.1304$g01.285@trnddc01> Date: Mon, 01 May 2006 14:27:09 GMT "stargatesg1" wrote in message news:uKb4g.43$Nh7.12@trnddc01... > Anyone ever try using plastic drywall anchors for yagi antenna insulators? > I'm wondering how they will hold up to UV and the weather in general. > > Thanks, > RoD > >Hi Rod, Someone may have already given this response and I missed it. Charles Byers has both insulators and element "keepers" for the insulators. A Google search under this name should turn up the product. Seem to recall they are black delrin. 73, Dale W4OP Article: 223992 of rec.radio.amateur.antenna From: "Tom Donaly" Subject: Re: Velocity Factor and resonant frequency References: <1146380239.089435.216750@j33g2000cwa.googlegroups.com> <9731-44552433-56@storefull-3254.bay.webtv.net> <1146481819.035769.4590@y43g2000cwc.googlegroups.com> Message-ID: Date: Mon, 01 May 2006 15:37:29 GMT Dave wrote: > Yuri and Tom, > > AD Hominem gains nothing except to raise blood pressure and raise > hostility. It certainly does not contribute to the discussion. > > Reasonable people can and do disagree. > > Please, in the interest of Harmony and Respect, let's move on. > > /S/ Deacon Dave (Rev. Mr.), W1MCE > This is one Christian I can agree with. It's hard to see how anyone can get exercised over a coil of wire. 73, Tom Donaly, KA6RUH Article: 223993 of rec.radio.amateur.antenna From: "Dean Craft" References: <44560cd1_2@newsfeed.slurp.net> Subject: Re: A little more on missing degrees Message-ID: Date: Mon, 1 May 2006 11:41:58 -0400 "Richard Fry" wrote in message news:44560cd1_2@newsfeed.slurp.net... > > > An antenna * system * does not need to have X number of degrees to be > resonant. It only needs to have ~zero reactance at its feedpoint -- > which, for electrically short AND long radiators can be achieved by use of > a suitable matching network. > > Such networks don't add or subtract electrical degrees, however. They > only reduce/cancel the natural reactance of the physical radiator in use. > > RF The above post is without doubt, the clearest, cleanest and to the point statement of any made to date in this whole silly chain of posts! It demonstrates a clear and firm grasp of antenna theory. Something that is so obviously missing from 99 percent plus of the bulk of posts on the subject! Dean -- W4IHK Article: 223994 of rec.radio.amateur.antenna From: "Robert Lay (W9DMK)" Subject: Re: spectral power density Date: Mon, 01 May 2006 12:26:29 -0400 Message-ID: References: <1146491265.725531.281770@i39g2000cwa.googlegroups.com> On 1 May 2006 06:47:45 -0700, "electro" wrote: >under unlicensed 2.4GHz FCC part 15 for digital modulation >system(non-spread spectrum), it says that the >1. maximum conducted power is 1W >2. the spectral density be not greater than 8dB for every 3khz band >during continous transmission >3. the 6-dB bandwith is at least 500khz > >question: >1. what is spectral density in this sense and its significance? >2. how can i measure my spectral density? >3. how does 1, 2 and 3 relate to each other? This is just a guess, but let's see what we can do to make some sense out of this. If you were hoping that the 1 watt of power would be evenly distributed across the 3 kHz bandwidth, that would be for the purpose of making sure that no one would be putting all of his 1 watt into a single frequency, which would be quite a strong concentration of power in comparison to having it spread out over the 3 kHz. The idea being that the power when concentrated is very noticeable and might cause QRM, whereas the same wattage spread out evenly over 3 kHz would barely exceed the background noise and would not be noticeable. So, you might want to require that signals not be very "peaky", or concentrated. In order to put limitations on "peakiness", you might require it to be "at least so wide" and "no higher than x" in units of spectral density. Assume that in the above requirement that the 500 Hz bandwidth requirement is to be interpreted as their requirement that avoids the signal being concentrated in a narrow band of frequencies. Also assume that the maximum power density in that 500 Hz bandwidth should be commensurate with the entire 1 watt being distributed over only 500 Hz instead of 3 kHz. Notice how we have traded off the requirements so that they are being applied to 1/6th of the 3 kHz. If we are allowed to concentrate all of our power in 1/6th of the bandwidth, then it follows that we would be required to keep the power density in that bandwidth at no higher than 6X the level it would have when spread out over the entire 3 kHz. I find that it is probably not a coincidence that the 6:1 ratio is almost exactly 8 dB in power ratio. Article: 223995 of rec.radio.amateur.antenna From: Fred Subject: Re: blame the posters not arrl Message-ID: <5jhc52939d5i1334sj0gq88kmsfc8eii1f@4ax.com> References: <1146271643.734737.155940@j73g2000cwa.googlegroups.com> <3lm5521h52e4jgalekjqq6g64e3i59u1mm@4ax.com> <1146333073.590407.297500@i39g2000cwa.googlegroups.com> <1257hrlls8jm694@corp.supernews.com> <33aa52hjph9c5e7bv6a0ihoonjttmsa7q4@4ax.com> <1146434087.455556.152410@u72g2000cwu.googlegroups.com> <13ja521a4t9lajqiiajd47h1siohf5vf8h@4ax.com> <1146449543.853365.112330@j73g2000cwa.googlegroups.com> Date: Mon, 01 May 2006 17:35:10 GMT On 30 Apr 2006 19:12:23 -0700, "an old friend" wrote: > >Fred wrote: >> On 30 Apr 2006 14:54:47 -0700, "an old friend" >? >> > >> >I have a valid license and radio equipment what would I need a waver >> >for? >> >> Hmmm, you tell us. >why? > >you are making the charge you suport >>You certainly don't seem too bright. I am merely >> making an observation of a known quantity. You act like a retard so >> therefore I assume that you are a retard. Die of HIV, loser. > >you just engage in libel and don't post anything on radio I do but you >don't Is it libel or an observation made of your behavior? If you don't want to be thought of as a retard, then learn how to spell and interact with other human beings. Things might change, but for now everyone has a negative perception of you and I am sure we all want you to die from HIV. I am still waiting for a radio post by you. Article: 223996 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: A little more on missing degrees References: <44560cd1_2@newsfeed.slurp.net> Message-ID: Date: Mon, 01 May 2006 17:47:26 GMT Dean Craft wrote: > The above post is without doubt, the clearest, cleanest and to the point > statement of any made to date in this whole silly chain of posts! It > demonstrates a clear and firm grasp of antenna theory. A self-resonant coil is obviously 90 degrees long. If one removes 5% of the turns and replaces them with a stinger to bring the system back to resonance at the same frequency, do you really believe the coil has magically changed from 90 degrees long to zero degrees long? -- 73, Cecil http://www.qsl.net/w5dxp Article: 223997 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Wire diameter vs Impedance References: <1146256136.332525.320580@i39g2000cwa.googlegroups.com> <1146504560.509236.51040@j33g2000cwa.googlegroups.com> Message-ID: Date: Mon, 01 May 2006 18:09:57 GMT K7ITM wrote: > But to > invoke "velocity factor" assumes something about the solution which may > well lead you away from the correct explanation. For the feedpoint impedance to be purely resistive, i.e. resonant, for a standing wave antenna, the reflected wave must get back into phase with the forward wave. Velocity factor is a way of explaining how/why that happens. The diameter of the conductor no doubt appears in the VF equation. -- 73, Cecil http://www.qsl.net/w5dxp Article: 223998 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Wire diameter vs Impedance References: <1146256136.332525.320580@i39g2000cwa.googlegroups.com> <1146504560.509236.51040@j33g2000cwa.googlegroups.com> <1146507445.103318.321540@j73g2000cwa.googlegroups.com> Message-ID: <1Bs5g.392$fb2.83@newssvr27.news.prodigy.net> Date: Mon, 01 May 2006 18:38:53 GMT K7ITM wrote: > Thanks for fulfilling my expectation. EZNEC can be used to verify the relationship of conductor diameter to velocity factor. Once the conductor diameter exceeds a certain limit, the standing wave current at the ends of that conductor undergo a 180 degree phase change, indicating a longer length than resonance. Tom, when you can determine the position and velocity of every electron in the system, please get back to us. :-) -- 73, Cecil http://www.qsl.net/w5dxp Article: 223999 of rec.radio.amateur.antenna From: Butch Magee Subject: Re: Plastic Antenna Insulators Date: Mon, 01 May 2006 15:00:44 -0500 Message-ID: <125cq81luegl75b@corp.supernews.com> References: stargatesg1 wrote: > Anyone ever try using plastic drywall anchors for yagi antenna insulators? > I'm wondering how they will hold up to UV and the weather in general. > > Thanks, > RoD > > Go to a new home site (under construction) and pick up a few inches of PVC 1/2 in. or 3/4 in. cut them to an appealing size and drill some holes in them at their ends and BAM, insulators! I like mine professional looking so I buy them from Buxcomm.com. They are inexpensive and in several designs or styles and Buck got good prices too!! Butch KF5DE Article: 224000 of rec.radio.amateur.antenna From: "Richard Fry" References: <44560cd1_2@newsfeed.slurp.net> Subject: Re: A little more on missing degrees Date: Mon, 1 May 2006 15:08:54 -0500 Message-ID: <44566a12_1@newsfeed.slurp.net> "Cecil Moore" > A self-resonant coil is obviously 90 degrees long. _____________ A coil is not the electrical equivalent of a linear, physical, ~90-degree, self-resonant radiator. How well do you expect your self-resonant coil to radiate? When you add a stinger to a coil, it is the stinger that radiates the great majority of the applied power. The coil just makes it possible/practical for the tx to supply r-f power to that antenna system that the stinger CAN radiate, by improving the Z match between the source and the feedpoint. RF Article: 224001 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Wire diameter vs Impedance Date: Mon, 01 May 2006 13:45:52 -0700 Message-ID: <125css3of7lppba@corp.supernews.com> References: <1146256136.332525.320580@i39g2000cwa.googlegroups.com> <1146504560.509236.51040@j33g2000cwa.googlegroups.com> <1146507445.103318.321540@j73g2000cwa.googlegroups.com> <1Bs5g.392$fb2.83@newssvr27.news.prodigy.net> Reg Edwards wrote: > > A cylinder has a flat circular end. Antenna wires and rods are > cylinders. You should be reminded that the true length of the antenna > is its straight length PLUS the radius of the flat circular end. > ---- > Reg. What do you mean by "true" length? Roy Lewallen, W7EL Article: 224002 of rec.radio.amateur.antenna From: "Dean Craft" References: <44560cd1_2@newsfeed.slurp.net> Subject: Re: A little more on missing degrees Message-ID: Date: Mon, 1 May 2006 17:11:28 -0400 "Dave" wrote in message news:NoGdnQPKKNlK9svZnZ2dnUVZ_vudnZ2d@comcast.com... > Dean Craft wrote: > > SNIPPED >> >> The above post is without doubt, the clearest, cleanest and to the point >> statement of any made to date in this whole silly chain of posts! It >> demonstrates a clear and firm grasp of antenna theory. Something that is >> so obviously missing from 99 percent plus of the bulk of posts on the >> subject! >> >> Dean -- W4IHK >> >> > > Dean, maybe we can start a discussion about the missing 1% > > "Something that is so obviously missing from 99 percent..." > I have all but given up on that possibility. If its not heated immature school yard rhetoric driven by obvious professional jealousy, then its mind playing games just as has appeared since my earlier post. The troll effect all too frequently takes over and destroys any serious chain of thought. Dean -- W4IHK Article: 224003 of rec.radio.amateur.antenna From: "Yuri Blanarovich" References: <2adc521i9itsa47hsbqcp0tnok4ml8c5ov@4ax.com> Subject: Re: Insulation diameter vs Impedance OR how to get 20dBi out of a short Dipole Message-ID: Date: Mon, 1 May 2006 17:24:48 -0400 "Richard Clark" wrote in message news:2adc521i9itsa47hsbqcp0tnok4ml8c5ov@4ax.com... > > Further, I do have access to a bulk of work employing water loaded > antennas (peer reviewed and not just more vanity publishing) that can > be used to test reality against theory (as corrupted as it may be by > the aberration factor). > > 73's > Richard Clark, KB7QHC OK, here is the one for the experienced and theoriticians: How about antenna made of wires, submerged just below the surface of water, partially salinated (brakish) or sea water. Would it couple to this huge "water antenna" (variations of insulated vs. bare elements) or connect/tap to it? One experience in this area was, when I operated from VE1ZZ on 160, he has one Eu Beverage that is terminated on the stainless steel hubcap in the ocean. That sucker beats any other "superior" beverages (staggered or phased pairs). Yuri, K3BU Article: 224004 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Wire diameter vs Impedance Date: Mon, 01 May 2006 14:48:38 -0700 Message-ID: <125d0hqiq1jstb3@corp.supernews.com> References: <1146256136.332525.320580@i39g2000cwa.googlegroups.com> <1146504560.509236.51040@j33g2000cwa.googlegroups.com> <1146507445.103318.321540@j73g2000cwa.googlegroups.com> <1Bs5g.392$fb2.83@newssvr27.news.prodigy.net> <125css3of7lppba@corp.supernews.com> Reg Edwards wrote: >> What do you mean by "true" length? >> >> > You know very well what I mean. Have you nothing else better to do > with your time? No, I don't know what you mean. And your response doesn't give me a great deal of confidence that you do, either. The reactance of an infinitely thin half wavelength dipole is 42.5 ohms, meaning that it isn't resonant. An infinitely thin dipole of length 0.496 wavelength, or about 1% shorter, is resonant. So my first question is whether the "true length" of an infinitesimally thin resonant dipole is 0.496 or 0.5 wavelength. (If 1% is too little to quibble about, why are we concerned about a length difference of a wire diameter?) If we increase the diameter of the antenna to 1/50 its length, the "true length" would then be 1.02 times the "true length" of the infinitesimally thin dipole. Yet we have to reduce the antenna length by nearly 7% to maintain resonance. So the "true length" doesn't have anything obvious to do with resonant length, nor does it provide a way to predict the resonant length based on wire diameter. If the meaning of "true length" is obvious, most other readers must know what it means. Would someone please be so kind as to explain to me what it means and how it's used? Roy Lewallen, W7EL Article: 224005 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Insulation diameter vs Impedance OR how to get 20dBi out of a Date: Mon, 01 May 2006 15:11:42 -0700 Message-ID: <125d1t27uta90a3@corp.supernews.com> References: <2adc521i9itsa47hsbqcp0tnok4ml8c5ov@4ax.com> Yuri Blanarovich wrote: > > OK, here is the one for the experienced and theoriticians: > > How about antenna made of wires, submerged just below the surface of water, > partially salinated (brakish) or sea water. Would it couple to this huge > "water antenna" (variations of insulated vs. bare elements) or connect/tap > to it? I don't understand. You're asking about the coupling between a submerged antenna made of wires and a "water antenna"? What's a "water antenna"? How close together are the two antennas? Any submerged antenna would have to be very shallow if it's to receive signals from above the water -- the attenuation of fields traveling through salt water is very high (~16 dB/foot at 1.8 MHz). If it's very deep, it might as well not be there at all. Roy Lewallen, W7EL Article: 224006 of rec.radio.amateur.antenna Date: Mon, 01 May 2006 19:16:13 -0400 From: jawod Subject: Re: blame the posters not arrl References: <1146271643.734737.155940@j73g2000cwa.googlegroups.com> <3lm5521h52e4jgalekjqq6g64e3i59u1mm@4ax.com> <1146333073.590407.297500@i39g2000cwa.googlegroups.com> <1257hrlls8jm694@corp.supernews.com> <33aa52hjph9c5e7bv6a0ihoonjttmsa7q4@4ax.com> <1146434087.455556.152410@u72g2000cwu.googlegroups.com> <13ja521a4t9lajqiiajd47h1siohf5vf8h@4ax.com> <1146449543.853365.112330@j73g2000cwa.googlegroups.com> <5jhc52939d5i1334sj0gq88kmsfc8eii1f@4ax.com> Message-ID: Fred wrote: > On 30 Apr 2006 19:12:23 -0700, "an old friend" > wrote: > > >>Fred wrote: >> >>>On 30 Apr 2006 14:54:47 -0700, "an old friend" >> >>? >> >>>>I have a valid license and radio equipment what would I need a waver >>>>for? >>> >>>Hmmm, you tell us. >> >>why? >> >>you are making the charge you suport >> >>>You certainly don't seem too bright. I am merely >>>making an observation of a known quantity. You act like a retard so >>>therefore I assume that you are a retard. Die of HIV, loser. >> >>you just engage in libel and don't post anything on radio I do but you >>don't > > > Is it libel or an observation made of your behavior? If you don't want > to be thought of as a retard, then learn how to spell and interact > with other human beings. Things might change, but for now everyone has > a negative perception of you and I am sure we all want you to die from > HIV. I am still waiting for a radio post by you. Fred, let it go, man Do YOU have anything related to ham radio to post? Article: 224007 of rec.radio.amateur.antenna From: "Yuri Blanarovich" References: <2adc521i9itsa47hsbqcp0tnok4ml8c5ov@4ax.com> <125d1t27uta90a3@corp.supernews.com> Subject: "Ocean as antenna" Message-ID: Date: Mon, 1 May 2006 19:32:20 -0400 Let me change the subject, in order not to interfere with original thread. OK, let me try to elaborate based on what I know and have observed. We know about the effect of distilled water on submerged radiator, it shrinks the dimensions due to dielectric constant. I am not going to distill the Barnegat Bay. We know that salt water or brackish water have high conductivity and act to radio waves as reflector and we can take the advantage of this property by using suitable antenna over or next to it. There is low penetration of such water surface by radio waves, but there should be some RF currents induced close to the surface of said water, (da poor conductor). The question: is there concentration of induced RF currents near the surface, and if so, can we tap them by furnishing proper antenna - transducer? It may be that the whole sandwich of water is just shunted to ground, or is there enough resistance between the ground and surface to allow enough of workable current/signal to collect. The idea is to "gamma match" the giant "water antenna" which is the water surface, in similar fashion as it is done say with aircraft body surface and a slot (antenna). I do not remember this mentioned in the books I have and I wonder if it is possible to harness the ocean as an antenna. Jus' wanted to make sure we do not overlook potential "antenna" at our feet. 73 Yuri, K3BU "Roy Lewallen" wrote in message news:125d1t27uta90a3@corp.supernews.com... > Yuri Blanarovich wrote: >> >> OK, here is the one for the experienced and theoriticians: >> >> How about antenna made of wires, submerged just below the surface of >> water, partially salinated (brakish) or sea water. Would it couple to >> this huge "water antenna" (variations of insulated vs. bare elements) or >> connect/tap to it? > > I don't understand. You're asking about the coupling between a submerged > antenna made of wires and a "water antenna"? What's a "water antenna"? How > close together are the two antennas? > > Any submerged antenna would have to be very shallow if it's to receive > signals from above the water -- the attenuation of fields traveling > through salt water is very high (~16 dB/foot at 1.8 MHz). If it's very > deep, it might as well not be there at all. > > Roy Lewallen, W7EL Article: 224008 of rec.radio.amateur.antenna Subject: Re: blame the posters not arrl From: Steveo Message-ID: <20060501194523.665$XK@newsreader.com> References: <1146271643.734737.155940@j73g2000cwa.googlegroups.com> <3lm5521h52e4jgalekjqq6g64e3i59u1mm@4ax.com> <1146333073.590407.297500@i39g2000cwa.googlegroups.com> <1257hrlls8jm694@corp.supernews.com> <33aa52hjph9c5e7bv6a0ihoonjttmsa7q4@4ax.com> <1146434087.455556.152410@u72g2000cwu.googlegroups.com> <13ja521a4t9lajqiiajd47h1siohf5vf8h@4ax.com> <1146449543.853365.112330@j73g2000cwa.googlegroups.com> <5jhc52939d5i1334sj0gq88kmsfc8eii1f@4ax.com> Date: 01 May 2006 23:29:43 GMT jawod wrote: > Do YOU have anything related to ham radio to post? > Well to be fair it can pertain to any of these groups.. rec.radio.amateur.antenna,rec.radio.amateur.equipment, rec.radio.amateur.policy,rec.radio.cb,rec.radio.shortwave Article: 224009 of rec.radio.amateur.antenna From: Fred Subject: Re: blame the posters not arrl Message-ID: <23cd521iser4stop3dd1q02s8vrhru353u@4ax.com> References: <3lm5521h52e4jgalekjqq6g64e3i59u1mm@4ax.com> <1146333073.590407.297500@i39g2000cwa.googlegroups.com> <1257hrlls8jm694@corp.supernews.com> <33aa52hjph9c5e7bv6a0ihoonjttmsa7q4@4ax.com> <1146434087.455556.152410@u72g2000cwu.googlegroups.com> <13ja521a4t9lajqiiajd47h1siohf5vf8h@4ax.com> <1146449543.853365.112330@j73g2000cwa.googlegroups.com> <5jhc52939d5i1334sj0gq88kmsfc8eii1f@4ax.com> Date: Tue, 02 May 2006 01:07:16 GMT On Mon, 01 May 2006 19:16:13 -0400, jawod wrote: >Fred wrote: >> On 30 Apr 2006 19:12:23 -0700, "an old friend" >> wrote: >> >> >>>Fred wrote: >>> >>>>On 30 Apr 2006 14:54:47 -0700, "an old friend" >>> >>>? >>> >>>>>I have a valid license and radio equipment what would I need a waver >>>>>for? >>>> >>>>Hmmm, you tell us. >>> >>>why? >>> >>>you are making the charge you suport >>> >>>>You certainly don't seem too bright. I am merely >>>>making an observation of a known quantity. You act like a retard so >>>>therefore I assume that you are a retard. Die of HIV, loser. >>> >>>you just engage in libel and don't post anything on radio I do but you >>>don't >> >> >> Is it libel or an observation made of your behavior? If you don't want >> to be thought of as a retard, then learn how to spell and interact >> with other human beings. Things might change, but for now everyone has >> a negative perception of you and I am sure we all want you to die from >> HIV. I am still waiting for a radio post by you. >Fred, let it go, man Since someone sane asked politely. No problem man. I'll be good for now. >Do YOU have anything related to ham radio to post? Maybe, but I am more of a reader than a writer. Article: 224010 of rec.radio.amateur.antenna Subject: Re: blame the posters not arrl From: Steveo Message-ID: <20060501211403.555$Yi@newsreader.com> References: <3lm5521h52e4jgalekjqq6g64e3i59u1mm@4ax.com> <1146333073.590407.297500@i39g2000cwa.googlegroups.com> <1257hrlls8jm694@corp.supernews.com> <33aa52hjph9c5e7bv6a0ihoonjttmsa7q4@4ax.com> <1146434087.455556.152410@u72g2000cwu.googlegroups.com> <13ja521a4t9lajqiiajd47h1siohf5vf8h@4ax.com> <1146449543.853365.112330@j73g2000cwa.googlegroups.com> <5jhc52939d5i1334sj0gq88kmsfc8eii1f@4ax.com> <23cd521iser4stop3dd1q02s8vrhru353u@4ax.com> Date: 02 May 2006 00:58:23 GMT Fred wrote: > Maybe, but I am more of a reader than a writer. > Mee two! Article: 224011 of rec.radio.amateur.antenna From: "Yuri Blanarovich" References: <2adc521i9itsa47hsbqcp0tnok4ml8c5ov@4ax.com> <125d1t27uta90a3@corp.supernews.com> Subject: Re: "Ocean as antenna" Message-ID: <5rz5g.80$N11.26@fe08.lga> Date: Mon, 1 May 2006 22:26:04 -0400 "Dave" wrote > Sorry for the top post. > > can the premise be restated as follows: > > "Could an insulated wire in a lossy conductive medium [AKA ocean water] > near the surface be modeled as a slot antenna in a lossy plane?" > > + + + and... if there is such an effect what is the best way to "catch the RF waves" grazing the shining ocean surface. More like - can it work besides just being modeled? I have been using "dog loop" antenna, originally RF dog fence around 3/4 acre lot, which is basically wire loop burried about 1 inch below the surface. It has about 600 ohms and works like a goofy Beverage, low noise pickup and still delivering reasonable signal on 80/160. That's why this bugs me, like using floating antenna? Just wondering if there is any potential in this or if anything was written up in the antenna books pro or con. Yuri, K3BU/mm > > Yuri Blanarovich wrote: > >> Let me change the subject, in order not to interfere with original >> thread. >> >> OK, let me try to elaborate based on what I know and have observed. >> >> We know about the effect of distilled water on submerged radiator, it >> shrinks the dimensions due to dielectric constant. I am not going to >> distill the Barnegat Bay. >> >> We know that salt water or brackish water have high conductivity and act >> to radio waves as reflector and we can take the advantage of this >> property by using suitable antenna over or next to it. >> >> There is low penetration of such water surface by radio waves, but there >> should be some RF currents induced close to the surface of said water, >> (da poor conductor). >> >> The question: >> is there concentration of induced RF currents near the surface, and if >> so, can we tap them by furnishing proper antenna - transducer? >> It may be that the whole sandwich of water is just shunted to ground, or >> is there enough resistance between the ground and surface to allow enough >> of workable current/signal to collect. >> The idea is to "gamma match" the giant "water antenna" which is the water >> surface, in similar fashion as it is done say with aircraft body surface >> and a slot (antenna). >> >> I do not remember this mentioned in the books I have and I wonder if it >> is possible to harness the ocean as an antenna. Jus' wanted to make sure >> we do not overlook potential "antenna" at our feet. >> >> 73 Yuri, K3BU >> >> >> >> >> "Roy Lewallen" wrote in message >> news:125d1t27uta90a3@corp.supernews.com... >> >>>Yuri Blanarovich wrote: >>> >>>>OK, here is the one for the experienced and theoriticians: >>>> >>>>How about antenna made of wires, submerged just below the surface of >>>>water, partially salinated (brakish) or sea water. Would it couple to >>>>this huge "water antenna" (variations of insulated vs. bare elements) or >>>>connect/tap to it? >>> >>>I don't understand. You're asking about the coupling between a submerged >>>antenna made of wires and a "water antenna"? What's a "water antenna"? >>>How close together are the two antennas? >>> >>>Any submerged antenna would have to be very shallow if it's to receive >>>signals from above the water -- the attenuation of fields traveling >>>through salt water is very high (~16 dB/foot at 1.8 MHz). If it's very >>>deep, it might as well not be there at all. >>> >>>Roy Lewallen, W7EL >> >> >> > Article: 224012 of rec.radio.amateur.antenna From: richardharrison@webtv.net (Richard Harrison) Subject: Re: A little more on missing degrees Date: Mon, 1 May 2006 22:59:20 -0500 Message-ID: <20715-4456D918-374@storefull-3255.bay.webtv.net> References: <44560cd1_2@newsfeed.slurp.net> Richard Fry wrote: "Such networks don`t add or subtract electrical degrees, however. They only reduce/cancel the natural reactance of the physical radiator in use." True if the only mismatch is reactance. A too-long antenna can be electrically shortened for matching purposes by tuning it to resonance with the proper series capacitance. A too-short antenna can be electrically lengthened for matching purposes by tuning it to resonance with the proper series inductance. Reactance varies quickly near the resonant length. Radiation resistance varies more slowly tending to increase at a steady rate as the antenna is lengthened. What radiates is current in a length of antenna. What gets current into an antenna is a conjugate match. Reactance is zeroed out, and source and load resistances are matched. That`s what`s needed for maximum power transfer between generator and antenna. Analysis may have been more abundant than needed for practical purposes. The velocity of current through a coil has been disputed. Some said it was almost instantaneous. That was new to me. The nature of inductance is to produce counter emf which by Lenz`s law opposes current into an inductance and temporarily delays current changes in an inductance. Only in a pure resistance is there instantaneous correlation between voltage and current. It is believed that the speed of light "c" is a speed limit on electromagnetic waves. An action in one place must have a delayed response elsewhere depending on distance. I can imagine a wave launched at one of an inductor sweeping across its length and ignoring the round and round path of the wire, but I don`t know of any of the old authors in my collection who say that such a short-cut happens. Conductors are the source of free electrons which permit current flow and my experience is that electricity goes where it is wired. Best regards, Richard Harrison, KB5WZI Article: 224013 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: "Ocean as antenna" Date: Tue, 02 May 2006 02:55:39 -0700 Message-ID: <125eb4vq5mbb030@corp.supernews.com> References: <2adc521i9itsa47hsbqcp0tnok4ml8c5ov@4ax.com> <125d1t27uta90a3@corp.supernews.com> <5rz5g.80$N11.26@fe08.lga> Yuri Blanarovich wrote: > "Dave" wrote > Sorry for the top post. >> can the premise be restated as follows: >> >> "Could an insulated wire in a lossy conductive medium [AKA ocean water] >> near the surface be modeled as a slot antenna in a lossy plane?" No. To my knowledge, a slot antenna requires a thin plane, which an ocean doesn't resemble. I imagine you could make one in a solid like a chunk of metal, but believe that the hole depth would have to be a substantial fraction of a wavelength. >> >> + + + > > and... > if there is such an effect what is the best way to "catch the RF waves" > grazing the shining ocean surface. More like - can it work besides just > being modeled? Not sure what effect you mean. But NEC-4 models interactions at, above, and below a medium like water with reasonable accuracy. > I have been using "dog loop" antenna, originally RF dog fence around 3/4 > acre lot, which is basically wire loop burried about 1 inch below the > surface. It has about 600 ohms and works like a goofy Beverage, low noise > pickup and still delivering reasonable signal on 80/160. That's why this > bugs me, like using floating antenna? I think you'll find that a buried antenna will work more and more poorly as the ground conductivity gets better and better. As an extreme, how well do you think it would work if buried in an Earth-sized chunk of metal? > Just wondering if there is any potential in this or if anything was written > up in the antenna books pro or con. I think you're on your own. The path is clear for you to be the first to make great discoveries! Just be sure to take a little time off along the way to do make those coil measurements. Roy Lewallen, W7EL Article: 224014 of rec.radio.amateur.antenna From: "amdx" Subject: help with rotor brands Date: Tue, 2 May 2006 05:53:57 -0500 Message-ID: <25d5f$44573a3c$45011502$10993@KNOLOGY.NET> Hi All, I'm searching for a rotor to use with a Flag antenna (as in Flag/Pennant). At present I'm using an Alliance U110 tv antenna rotor. I'm rebuilding my Flag and it will a bit heavier and has lots of leverage, 15ft each side of the mast. The tv rotor seems to have been fine in the past but I need a control unit that is SILENT. The Alliance control unit does the Clunk, Clunk, Clunk as the mast rotates. I don't know any brands or specifications so all info is appreciated. Thanks Mike PS. Is there a group or reflector that might be a better resource for this question? Article: 224015 of rec.radio.amateur.antenna From: gwatts Subject: Re: "Ocean as antenna" References: <2adc521i9itsa47hsbqcp0tnok4ml8c5ov@4ax.com> <125d1t27uta90a3@corp.supernews.com> <5rz5g.80$N11.26@fe08.lga> Message-ID: <01I5g.7626$kg.789@news02.roc.ny> Date: Tue, 02 May 2006 12:26:28 GMT Yuri Blanarovich wrote: ... > and... > if there is such an effect what is the best way to "catch the RF waves" > grazing the shining ocean surface. More like - can it work besides just > being modeled? From http://www.mso.anu.edu.au/cas/presents/don.html I quote "Joe Pawsey took me up to Dover Heights that first day to the cliff-top interferometer. It was a very cunning device. As the sun rose above the ocean there was a reflected ray off the ocean, received by the antenna, and then the direct ray; this formed an interferometer - like a Lloyds mirror type thing - this was the array that found that the Crab Nebula was a radio source, and also did much of the early work on Cygnus" Article: 224016 of rec.radio.amateur.antenna From: John - KD5YI Subject: Re: Wire diameter vs Impedance - correction References: <1146256136.332525.320580@i39g2000cwa.googlegroups.com> <1146416277.330091.189340@j73g2000cwa.googlegroups.com> <125a5f49sbulm23@corp.supernews.com> <1146453135.097754.114450@y43g2000cwc.googlegroups.com> <1146453869.698696.76370@j73g2000cwa.googlegroups.com> <1mz5g.10477$t_2.2965@trnddc07> Message-ID: <_JI5g.8915$nV4.6491@trnddc04> Date: Tue, 02 May 2006 13:00:42 GMT Reg Edwards wrote: >>So, if Length / Dia equals e / 4 (about .67957), then C = infinite? >> > > ==================================== > C even goes negative for smaller values of Length/Dia. > > I'll let you into a secret - the formulae are approximate and don't > apply when antenna length is less than about 5 times its diameter. > > When was the last time you saw an antenna wire only 5 times longer > than its diameter? > > You should supply your "secrets" along with your formulae. Article: 224017 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: A little more on missing degrees References: <44560cd1_2@newsfeed.slurp.net> <44566a12_1@newsfeed.slurp.net> Message-ID: Date: Tue, 02 May 2006 13:52:48 GMT Richard Fry wrote: > "Cecil Moore" >> A self-resonant coil is obviously 90 degrees long. > A coil is not the electrical equivalent of a linear, physical, > ~90-degree, self-resonant radiator. How well do you expect your > self-resonant coil to radiate? Not very well. Nobody is saying that a coil is a good radiator. It probably radiates about as much RF as a piece of wire of the same axial length as the coil. Nothing about the discussion of phase shift through a coil has had anything to do with radiation. In fact, I have ignored radiation from the coil in all of my calculations since I consider it to be negligible. We have a phase shift in a transmission line with negligible radiation. The same is true of a loading coil. > When you add a stinger to a coil, it is the stinger that radiates the > great majority of the applied power. Absolutely no question about that. The round and round design of a coil makes it more akin to a piece of transmission line than it does to a radiator. But like a transmission line stub, it contributes a phase shift to the system. The stub on a properly designed J-Pole doesn't radiate much either. But one can certainly calculate the phase shift from the feedpoint to bottom of the radiating element. Again, the phase shift in the coil has virtually nothing to do with how much the coil radiates. Looking at just one turn on the coil, the current on each side of the turn is approximately equal magnitude and flowing in opposite directions (just as in a transmission line). So virtually all the radiation is canceled by the opposite near fields (just as in a transmission line). -- 73, Cecil http://www.qsl.net/w5dxp Article: 224018 of rec.radio.amateur.antenna From: John - KD5YI Subject: Re: Wire diameter vs Impedance - correction References: <1146256136.332525.320580@i39g2000cwa.googlegroups.com> <1146416277.330091.189340@j73g2000cwa.googlegroups.com> <125a5f49sbulm23@corp.supernews.com> <1146453135.097754.114450@y43g2000cwc.googlegroups.com> <1146453869.698696.76370@j73g2000cwa.googlegroups.com> <1mz5g.10477$t_2.2965@trnddc07> <_JI5g.8915$nV4.6491@trnddc04> Message-ID: Date: Tue, 02 May 2006 14:00:47 GMT Reg Edwards wrote: >>You should supply your "secrets" along with your formulae. > > ===================================== > > At my time of life I don't have time to write a book! > > You'll just have to read between the lines. ;o) > ---- > Reg. > > Fine. From now on, I will assume you have no time to explain your "secrets" when you post so I will ignore your formulae. This approach is much better than being misled if I do not read between your lines properly. Article: 224019 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Wire diameter vs Impedance References: <1146256136.332525.320580@i39g2000cwa.googlegroups.com> <1146504560.509236.51040@j33g2000cwa.googlegroups.com> <1146507445.103318.321540@j73g2000cwa.googlegroups.com> <1Bs5g.392$fb2.83@newssvr27.news.prodigy.net> <1146528536.568289.29120@g10g2000cwb.googlegroups.com> Message-ID: <93K5g.71838$H71.57495@newssvr13.news.prodigy.com> Date: Tue, 02 May 2006 14:31:33 GMT K7ITM wrote: > Those sources also don't tell me anything about > "velocity factor" as far as I can tell. What RF engineers call "velocity factor" is related to the phase constant in the complex propagation constant embedded in any transmission line equation in any decent textbook. Do your sources tell you anything about the complex propagation constant? -- 73, Cecil http://www.qsl.net/w5dxp Article: 224020 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: A little more on missing degrees References: <44560cd1_2@newsfeed.slurp.net> <20715-4456D918-374@storefull-3255.bay.webtv.net> Message-ID: Date: Tue, 02 May 2006 14:45:45 GMT Richard Harrison wrote: > I can imagine a wave launched at one of an inductor sweeping across its > length and ignoring the round and round path of the wire, but I don`t > know of any of the old authors in my collection who say that such a > short-cut happens. Conductors are the source of free electrons which > permit current flow and my experience is that electricity goes where it > is wired. Consider a tank circuit link coupled to the outside world. There are probably negligible free electrons flowing from primary to secondary. Yet efficient energy transfer occurs when the coils are tightly coupled. In a loading coil, each turn is tightly coupled to the adjacent turn causing part of the current to be the result of the fields rather than wire path. That's why the VF of the loading coil is roughly double what it would be for "round and round the coil" calculations. The VF for a 75m bugcatcher coil appears to be in the ballpark of 0.04 which is a far cry from the straight across 1.0 or even 0.5 -- 73, Cecil http://www.qsl.net/w5dxp Article: 224021 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Wire diameter vs Impedance References: <1146256136.332525.320580@i39g2000cwa.googlegroups.com> <1146504560.509236.51040@j33g2000cwa.googlegroups.com> <1146507445.103318.321540@j73g2000cwa.googlegroups.com> <1Bs5g.392$fb2.83@newssvr27.news.prodigy.net> <1146528536.568289.29120@g10g2000cwb.googlegroups.com> <6eCdnYZlm9BIzMrZnZ2dnUVZ8qudnZ2d@bt.com> Message-ID: Date: Tue, 02 May 2006 14:55:32 GMT Reg Edwards wrote: > The "end-effect" occurs with any length of antenna. There are only two > ends. Is the lack of an "end-effect" why a full-wave loop has to be made longer than 2*468/f? -- 73, Cecil http://www.qsl.net/w5dxp Article: 224022 of rec.radio.amateur.antenna From: fmmck@aol.com (Fred McKenzie) Subject: Re: Gain of 2.4GHz WiFi vertical Date: Tue, 02 May 2006 12:18:07 -0400 Message-ID: References: <1146576950.559148.53790@j33g2000cwa.googlegroups.com> In article <1146576950.559148.53790@j33g2000cwa.googlegroups.com>, "pdrunen@aol.com" wrote: > Since the antenna is a vertical, I thought that the best low-angle > radiation is 5/8 wave for verticals, anything longer would put the > lobes higher and would result in a lower low angle gain. > > If this is the case then the antenna should only be about 3.5 inches > long. ? PD- The beauty of the 5/8 (0.625) wavelength groundplane antenna, is that its feedpoint impedance has a resistive component of 50 Ohms, and can easily be matched with a small inductor. Some such antennas have been constructed by winding the coil using the base of the antenna rod. It is my recollection from an antennas class 35 years ago, that the best signal towards the horizon comes from a 0.58 wavelength groundplane antenna, not 0.625 wavelength. I can see how 5/8 and 0.58 might be confused, and many may consider the difference trivial. As far as the D-Link antenna, it is most likely a co-axially fed vertical dipole with additional colinear elements separated by phasing networks. Fred Article: 224023 of rec.radio.amateur.antenna From: wood@itd.nrl.navy.mil (J. B. Wood) Subject: Re: Smith Chart inventor Date: Tue, 02 May 2006 12:59:47 -0400 Message-ID: References: <445138e4$0$1007$39cecf19@news.twtelecom.net> In article , "Reg Edwards" wrote: > "Jeff" wrote > > > Smith did not invent the Smith Chart. He simplified, for HF use > only, > > > charts which had been in existence since the Victorian Age, which > > > covered all transmission line frequenies down to telephone and > power > > > frequencies. > > > > > > > That is not quite correct, what Smith did was to take to concept of > the > > pre-existing equations and a rectangular chart which covered a > limited range > > of impedances and develop them into a circular, more complex chart, > that > > covered a full range of impedances. See the Introduction to Smith's > book > > "Electronic Applications of the Smith Chart". > > > > Regards > > Jeff > ========================================= > > Agreed. Your description of what Smith did is more accurate than > mine. > ---- > Reg. Hello, and there appears to be faulty logic here. Any other form of chart not in Smith's format or variants thereof (e.g. a Carter Chart) cannot be a Smith Chart. The fact that Phillip Smith's and similar types of charts are all based upon the transmission line equations is irrelevant to giving due credit to their respective developers. Smith recognizes (pg xv, intro to Smith's book) that similar charts (and their respective limitations) formulated by others inspired him. Do we say that since a couple of brothers from Dayton, Ohio leveraged then-existing aviation technologies and ideas developed by others (e.g. gliders) the Wrights shouldn't be given credit for inventing a successful human carrying, heavier-than-air, propeller-driven aircraft? And for the flip side, while many readily identify Marconi, DeForest, J. Fleming and sometimes Tesla as radio pioneers how many can recall Edwin Armstrong? Sincerely, and 73s from N4GGO, John Wood (Code 5550) e-mail: wood@itd.nrl.navy.mil Naval Research Laboratory 4555 Overlook Avenue, SW Washington, DC 20375-5337 Article: 224024 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Wire diameter vs Impedance References: <1146256136.332525.320580@i39g2000cwa.googlegroups.com> <1146504560.509236.51040@j33g2000cwa.googlegroups.com> <1146507445.103318.321540@j73g2000cwa.googlegroups.com> <1Bs5g.392$fb2.83@newssvr27.news.prodigy.net> <1146528536.568289.29120@g10g2000cwb.googlegroups.com> <6eCdnYZlm9BIzMrZnZ2dnUVZ8qudnZ2d@bt.com> Message-ID: Date: Tue, 02 May 2006 17:16:04 GMT Reg Edwards wrote: > Cec, I do wish you would stick to metric dimensions instead of feet > and inches. Sorry, Reg, I'm with the English on that one. :-) -- 73, Cecil http://www.qsl.net/w5dxp Article: 224025 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Wire diameter vs Impedance References: <1146256136.332525.320580@i39g2000cwa.googlegroups.com> <1146504560.509236.51040@j33g2000cwa.googlegroups.com> <1146507445.103318.321540@j73g2000cwa.googlegroups.com> <1Bs5g.392$fb2.83@newssvr27.news.prodigy.net> <1146528536.568289.29120@g10g2000cwb.googlegroups.com> <93K5g.71838$H71.57495@newssvr13.news.prodigy.com> Message-ID: Date: Tue, 02 May 2006 17:31:08 GMT Dave wrote: > Complex propagation constant is ? = ? +j? : > ? is the attenuation in Nepers/wavelength > ? is the phase shift in Radians/wavelength > Did I pass ?????????? If I remember correctly, SQRT(Z*Y) results in a dimensionless quantity. -- 73, Cecil http://www.qsl.net/w5dxp Article: 224026 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Gain of 2.4GHz WiFi vertical Date: Tue, 02 May 2006 12:17:29 -0700 Message-ID: <125fc2halekg7d4@corp.supernews.com> References: <1146576950.559148.53790@j33g2000cwa.googlegroups.com> Fred McKenzie wrote: > > The beauty of the 5/8 (0.625) wavelength groundplane antenna, is that its > feedpoint impedance has a resistive component of 50 Ohms, and can easily > be matched with a small inductor. Some such antennas have been > constructed by winding the coil using the base of the antenna rod. It is > my recollection from an antennas class 35 years ago, that the best signal > towards the horizon comes from a 0.58 wavelength groundplane antenna, not > 0.625 wavelength. I can see how 5/8 and 0.58 might be confused, and many > may consider the difference trivial. Maximum gain at the horizon actually occurs at around 0.625 wavelength. At lengths between 0.5 and 0.625, a higher angle lobe appears, but it doesn't divert a significant amount of the total power away from the main lobe until the antenna gets longer than 0.625 wavelength. However, those gain figures are for a vertical antenna mounted on a perfect, infinite, ground plane. Actual performance of 0.5 or 0.625 wavelength antennas compared to quarter wave ones varies a great deal in most typical situations. And any kind of WLAN device I've seen deviates in major ways from the ideal case. Gain of a longer antenna is as likely to be due to placebo effect as to physics. One big advantage of a 0.5 wavelength antenna is its high feedpoint impedance. This makes it much more independent of the other half of the antenna -- what amateurs like to call "ground", but is often the top of a car, a person holding an HT, a router box, etc. The advantage isn't shared by the 0.625 wavelength radiator. Roy Lewallen, W7EL Article: 224027 of rec.radio.amateur.antenna From: "J. Mc Laughlin" Subject: Re: Multi hopping radio waves Date: Tue, 2 May 2006 16:21:49 -0400 Message-ID: <125ffq9kpvg3kd6@corp.supernews.com> References: <19197-4450F612-273@storefull-3257.bay.webtv.net> Dear Group: The use of one number is crude and suitable only if one has imbibed enough grain alcohol or one does not care about Lord K's admonition or both. The preferred scheme is to model the expected virtual heights at each ionospheric reflection (note that the apparent TOA (angles) involved are not likely to be the same at each of these reflections) and then to use the angles involved to note the expected incidence angle of the intermediate "ground" reflection. The coordinates of the expected "ground" reflection areas are calculated and note is taken as to whether those areas are predominately salt-water, ice, or neither. A heuristic algorithm is applied that depends on type of "ground" and that weakly depends on the expected incidence angle. The result is a statistically significant reflection loss. [Some iteration is needed, which computers are very good at doing.] It is important to note that the apparent TOA of the major mode between two points is unlikely to be the same at both ends of the path because the virtual height is unlikely to be the same near both ends. For HF paths greater than something like 12 or 14 Mm predictions become more complex. In all cases of multiple hops (real DX), the TOA at which the gain of the antennas is effective varies between about 12 degrees and 2 degrees. If one wishes a simple predictor, one could find it in a paper published in the UK in the transactions on a conference on HF propagation in the 80s (as I recall) by a BBC engineer (IEE was the publisher). The entire computer code is given in the paper. It uses a simple heuristic model that was found by the BBC to give satisfactory results over the paths that their World Service used. Note that the BBC used paths that did not include much of the polar regions. To digress: The worst path to a DXCC entity from the Upper Midwest is over the magnetic pole to VU4. 100 watt transmitters, ice reflections, heavy absorption, and roughly 10 db more noise at the far end make the need for power and high antennas almost necessary. 73 Mac N8TT -- J. Mc Laughlin; Michigan U.S.A. Home: JCM@Power-Net.Net "Richard Harrison" wrote in message news:19197-4450F612-273@storefull-3257.bay.webtv.net... > > It could be right for some reflections. > > E.A. Laport was Chief Engineer of RCA International when he wrote "Radio > Antenna Engineering". On page 236 Fig. 3.17 shows the effect of ground > conductivity on maximum field strength from a horizontal dipole antenna > versus its height in vavelengths. > > Optimum height would be about 0,50 wavelength to most concentrate energy > at a certain vertical angle, 30-degrees according to the RAF Signal > Manual quoted by Laport. 30-degrees might hop 1000 kilometers. > > At the antenna earth reflection point, frequencies between 2 and 16 MHz > are reduced to 95% of their prereflection field strengths by ordinary > soil from a dipole at 1/2-wavelength height. A reduction to 70.7% of > prereflection strength would represent a 3 dB power loss. So no harm > done yet by the reflection from an antenna over good soil. Lower antenna > height and poorer soil would attenuate more. > > The angle at which rhe signal strikes the earth in subsequent > reflections should be the same as the first reflection from the antenna. > Conductivity and dielectric constant at subsequent earth reflection > points are what they are. > > Shortwave broadcasters use vertically stacked horizontal elements to > concentrate the vertical beam to avoid multipath interference. They also > prefer targets reached on the first reflection from the ionosphere.. > > Best regards, Richard Harrison, KB5WZI > Article: 224028 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Wire diameter vs Impedance Date: Tue, 02 May 2006 15:36:37 -0700 Message-ID: <125fnnqh54t48a7@corp.supernews.com> References: <1146256136.332525.320580@i39g2000cwa.googlegroups.com> <1146504560.509236.51040@j33g2000cwa.googlegroups.com> <1146507445.103318.321540@j73g2000cwa.googlegroups.com> <1Bs5g.392$fb2.83@newssvr27.news.prodigy.net> <1146528536.568289.29120@g10g2000cwb.googlegroups.com> <6eCdnYZlm9BIzMrZnZ2dnUVZ8qudnZ2d@bt.com> <1146596054.095856.75500@g10g2000cwb.googlegroups.com> "End effect" looks to me like a description of a result, not an explanation of a cause. Its "proof" consists of the observation that fatter dipoles have a shorter resonant length than thin ones. I'm afraid a real explanation of why the "end effect" occurs requires much deeper physics and math. I don't believe that Tom's result with the top hat is a demonstration of the same phenomenon that makes resonant fat dipoles shorter than thin ones. Here's what the top hat experiment means: Suppose you have a thin antenna of any length. Look at the current distribution on the last few degrees of the antenna. I believe you'll find that it's the same regardless of the antenna length. Then replace the wire with a top hat. Again you'll find that the current distribution on the top hat is the same regardless of the length of the antenna below it. So it shouldn't be surprising that you can substitute one for the other and get the same result regardless of the antenna length. This proves that you can replace a part of an antenna with a capacitive hat, and that the relationship between the length of wire and size of top hat is, at least to first order, independent of the antenna length. It's not clear to me what else it proves. Incidentally, does this have anything to do with the "true length" of an antenna? No one has stepped forward yet with an explanation. Roy Lewallen, W7EL Reg Edwards wrote: > Tom wrote - >> I also used NEC2 to simulate the effects of a small top-hat: it was > 4 >> radial wires at the top of a vertical, 0.001 wavelengths long. The >> vertical diameter was .000001 wavelengths (as were the radials > forming >> the top hat). I found that adding that top had reduced the length > for >> resonance by exactly the same length in each case, for 1/4, 2/4, 3/4 >> and 4/4 wave tall antennas, probably within the accuracy of the >> computing engine. > > ===================================== > > The "End Effect" is thereby proved. > > Marvellous things are computing engines! > ---- > Reg. > > Article: 224029 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Wire diameter vs Impedance References: <1146256136.332525.320580@i39g2000cwa.googlegroups.com> <1146504560.509236.51040@j33g2000cwa.googlegroups.com> <1146507445.103318.321540@j73g2000cwa.googlegroups.com> <1Bs5g.392$fb2.83@newssvr27.news.prodigy.net> <1146528536.568289.29120@g10g2000cwb.googlegroups.com> <6eCdnYZlm9BIzMrZnZ2dnUVZ8qudnZ2d@bt.com> <1146596054.095856.75500@g10g2000cwb.googlegroups.com> <125fnnqh54t48a7@corp.supernews.com> Message-ID: Date: Tue, 02 May 2006 22:52:24 GMT Roy Lewallen wrote: > Suppose you have a thin antenna of any length. Look at the current > distribution on the last few degrees of the antenna. I believe you'll > find that it's the same regardless of the antenna length. For a 1/2WL dipole, it is also the same at the center of the antenna and at all other points anywhere on the antenna. The standing wave current phase cannot be used to measure phase shift in a wire or a coil or a top hat or a stub. The phase of standing wave current is meaningless. If one makes the top hat large enough, one should see an abrupt ~180 phase reversal in the standing wave current. This happens on each side of a current minimum point. -- 73, Cecil http://www.qsl.net/w5dxp Article: 224030 of rec.radio.amateur.antenna From: richardharrison@webtv.net (Richard Harrison) Subject: Re: Multi hopping radio waves Date: Tue, 2 May 2006 20:16:04 -0500 Message-ID: <5950-44580454-606@storefull-3257.bay.webtv.net> References: <125ffq9kpvg3kd6@corp.supernews.com> Mac, N8TT wrote: "Note that the BBC used paths that did not include much of the polar regions." That`s an indication that they knew something about broadcasting. There must be a better way somewhere that doesn`t involve a path near a polar region. A broadcaster must advertise his programs well in advance. He can`t find a band that`s open and tailor his emissions to it. He must fire up on schedule with the right program at the designated time and direction regardless of conditions. All is planned long ahead of time. One of the most usless toys we had was a backscatter ionospheric sounder. It worked well but we had no immediate need for the information it provided. We were locked in our schedules for months in advance and today`s ionospheric conditions were short-term indeed. Best regards, Richard Harrison, KB5WZI Article: 224031 of rec.radio.amateur.antenna From: Bill Turner Subject: Re: Multi hopping radio waves Date: Tue, 02 May 2006 18:47:45 -0700 Message-ID: References: <125ffq9kpvg3kd6@corp.supernews.com> <5950-44580454-606@storefull-3257.bay.webtv.net> ORIGINAL MESSAGE: On Tue, 2 May 2006 20:16:04 -0500, richardharrison@webtv.net (Richard Harrison) wrote: >A broadcaster must advertise his programs well in advance. He can`t find >a band that`s open and tailor his emissions to it. He must fire up on >schedule with the right program at the designated time and direction >regardless of conditions. All is planned long ahead of time. *********** REPLY SEPARATOR *********** A good argument for moving international broadcast to the VHF/UHF or higher regions. HF was good when there were no alternatives, but the time has come to retire it. Bill, W6WRT Article: 224032 of rec.radio.amateur.antenna From: Buck Subject: Re: RoomCap Antenna Message-ID: <85vg52t9207ouotls9esq04ple5f3gc584@4ax.com> References: Date: Wed, 03 May 2006 05:49:56 -0400 On Wed, 03 May 2006 03:49:40 GMT, "Don" wrote: >try this one 73 ve7ado > >http://www.eh-antenna.com/library/EH_ANTENNA_FOR_HAMS.pdf > >"Buck" wrote in message >news:jb0a52t70cqcnl4o482hh815fkadf6hbmk@4ax.com... >> Can anyone tell me about this RoomCap Antenna? >> Thanks, Don. -- 73 for now Buck N4PGW Article: 224033 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: 4:1 balun question References: Message-ID: Date: Wed, 03 May 2006 13:16:39 GMT Dan Richardson wrote: > The Sept/Oct 2005 issue of QEX has a 4:1 balun design that may > interest you. It can be found on the ARRL's members only web site. Would a 4:1 voltage balun fed through a husky 1:1 choke (W2DU BALUN) accomplish the same thing? -- 73, Cecil http://www.qsl.net/w5dxp Article: 224034 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: 4:1 balun question References: Message-ID: Date: Wed, 03 May 2006 13:22:45 GMT Mike Coslo wrote: > Do the single core designs really not work? I had a single core > homebrew that seemed to work, but I'm a tad confused after hearing that > they don't. The single core designs are usually voltage baluns and what we hams want are balanced currents. I don't see why you couldn't just add a husky 1:1 W2DU style choke on the 50 ohm side of your 4:1 voltage balun to inhibit common mode current. The extra toroid in the afore mentioned QEX article is a 1:1 choke attached to a 4:1 voltage balun. -- 73, Cecil http://www.qsl.net/w5dxp Article: 224035 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: A little more on missing degrees References: <44560cd1_2@newsfeed.slurp.net> Message-ID: Date: Wed, 03 May 2006 14:04:39 GMT Dave wrote: > I gave up on the 'missing degrees' and all variations topic about 1 > month ago. Hit the KILL Button and read on! For those who didn't give up, here is a summary of what I was able to do with EZNEC. This exercise should be able to be repeated in the real world. 1. Using the helix feature of EZNEC, I created a 100 turn octagonal coil, 6 inches in diameter, 4 turns per inch. 2. I installed it as a base loading coil over a mininec ground plane and removed turns until it was self-resonant on 4 MHz. That left a total of 69 turns on a 1.435 foot long coil. Give that the coil is 90 degrees at the self- resonant frequency, I calculated a velocity factor of 0.023 for the coil. 3. The coil was then trimmed to half size, i.e. 34.5 turns. Assuming it was then 45 degrees long, the Z0 was determined to be approximately 2200 ohms by looking at the feedpoint impedance reported by EZNEC. 45 degrees from 0-j0 on the Smith Chart is at -j1.0. 4. A stinger was added to the above 45 degrees of coil to bring the antenna back to resonance on 4 MHz. It took 7 ft. of stinger, or 10.2 degrees. 10.2 degrees from 0-j*infinity on the Smith Chart is at -j4.8. 5. The ratio of -j4.8/-j1.0 is the ratio of the Z0 of the coil to the Z0 of the stinger. If the Z0 of the coil is indeed 2200 ohms, the Z0 of the stinger is 458 ohms, just about where it should be. The impedance discontinuity provides the "missing" ~35 degrees of the antenna. 6. Using Dr. Corum's equation for velocity factor yields 0.02 for that coil, a value 13% lower than the one predicted by EZNEC, well within the ballpark for expectations. My conclusions: The delay through a loading coil is in the tens of degrees. The delay through the elements of the antenna do not add up to 90 degrees. In the above EZNEC example, the delay from feedpoint to the tip of the antenna is only 55 degrees. The "missing" degrees are provided by the impedance discontinuity between the coil and the stinger. There is no real- time delay associated with those "missing" degrees. -- 73, Cecil http://www.qsl.net/w5dxp Article: 224036 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Wire diameter vs Impedance References: <1146256136.332525.320580@i39g2000cwa.googlegroups.com> <1146504560.509236.51040@j33g2000cwa.googlegroups.com> <1146507445.103318.321540@j73g2000cwa.googlegroups.com> <1Bs5g.392$fb2.83@newssvr27.news.prodigy.net> <1146528536.568289.29120@g10g2000cwb.googlegroups.com> <93K5g.71838$H71.57495@newssvr13.news.prodigy.com> Message-ID: Date: Wed, 03 May 2006 14:22:35 GMT Dave wrote: > Alpha and Beta got transformed into ? and j?. Gamma also got transformed > into ?. Now it makes more sense. :-) What is scarey is that some browsers may display Greek characters correctly and some may not. > What kind of bait are you throwing out about SQRT[Z*Y] ? Z is the distributed series impedance and Y is the distributed shunt admittance. The equation for the propagation constant is gamma = alpha + j*beta = SQRT(Z*Y). Doesn't multiplying an impedance by an admittance result in a dimensionless quantity? -- 73, Cecil http://www.qsl.net/w5dxp Article: 224037 of rec.radio.amateur.antenna From: "Robert Lay (W9DMK)" Subject: Re: spectral power density Date: Wed, 03 May 2006 10:32:46 -0400 Message-ID: References: <1146491265.725531.281770@i39g2000cwa.googlegroups.com> <1146496107.299262.109830@i40g2000cwc.googlegroups.com> <1146557393.583471.312740@u72g2000cwu.googlegroups.com> On 2 May 2006 01:09:53 -0700, "electro" wrote: >in other words, when i have a transmit modulation bandwith of 500kbps >my peak power level must be 8 dBm...right? No - that is not correct, in my opinion. My interpretation is that the spectral power density in a 500 Hz bandwidth must not exceed the limit of 2 milliwatts per Hz. (Simply spread the 1 watt over a width of 500 Hz. In my original post I thought your message said 500Hz. Now I see you are saying 500kHz. Which is correct? >what if i use 6khz or >5khz?does proportionality hold here or just say in any bandwith not >greater than 500khz, the peak power level should not always exceed >8dBm?.. The 8 dBm is a red-herring. I took your value of 8 dB as Gospel. If someone says 8 dB they don't mean 8 dBm and vice versa. Can you make sure of the accuracy of your excerpts, because I see nothing in the Part 15 regs that correlate with your numbers. In other words, I'm working with nothing but your excerpts and common sense electrical engineering. Article: 224038 of rec.radio.amateur.antenna From: "Robert Lay (W9DMK)" Subject: Re: A little more on missing degrees Date: Wed, 03 May 2006 10:47:07 -0400 Message-ID: References: <44560cd1_2@newsfeed.slurp.net> <20715-4456D918-374@storefull-3255.bay.webtv.net> On Mon, 1 May 2006 22:59:20 -0500, richardharrison@webtv.net (Richard Harrison) wrote: >Richard Fry wrote: >"Such networks don`t add or subtract electrical degrees, however. They >only reduce/cancel the natural reactance of the physical radiator in >use." > >True if the only mismatch is reactance. A too-long antenna can be >electrically shortened for matching purposes by tuning it to resonance >with the proper series capacitance. A too-short antenna can be >electrically lengthened for matching purposes by tuning it to resonance >with the proper series inductance. > >Reactance varies quickly near the resonant length. Radiation resistance >varies more slowly tending to increase at a steady rate as the antenna >is lengthened. > >What radiates is current in a length of antenna. What gets current into >an antenna is a conjugate match. Reactance is zeroed out, and source and >load resistances are matched. That`s what`s needed for maximum power >transfer between generator and antenna. > >Analysis may have been more abundant than needed for practical purposes. > >The velocity of current through a coil has been disputed. Some said it >was almost instantaneous. That was new to me. The nature of inductance >is to produce counter emf which by Lenz`s law opposes current into an >inductance and temporarily delays current changes in an inductance. Only >in a pure resistance is there instantaneous correlation between voltage >and current. Constraining the discussion to lumped circuit theory, the delay that you speak of would seem to be relevant if one is measuring transient response. However, for a steady-state a.c. current, is it not more appropriate to describe the relationship as a phase lag between the current through and the voltage across the inductor? Further, is it not the case that such phase difference is nominally fixed at near 90 degrees (for a high Q inductor), and is it not true that the velocity is nonetheless at the speed of light? > >It is believed that the speed of light "c" is a speed limit on >electromagnetic waves. An action in one place must have a delayed >response elsewhere depending on distance. > >I can imagine a wave launched at one of an inductor sweeping across its >length and ignoring the round and round path of the wire, but I don`t >know of any of the old authors in my collection who say that such a >short-cut happens. Conductors are the source of free electrons which >permit current flow and my experience is that electricity goes where it >is wired. > >Best regards, Richard Harrison, KB5WZI Article: 224039 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: A little more on missing degrees References: <44560cd1_2@newsfeed.slurp.net> Message-ID: Date: Wed, 03 May 2006 14:59:21 GMT Dave wrote: > In item 2 you make an unsupported statement: "Give that the coil is 90 > degrees at the self-resonant frequency,..." > > Self resonance only means that the capacitive and inductive reactances, > both distributed, are equal. That does not validate a 90 degree > assumption. Without that validation, IMO, the subsequent discussion is > questionable. Quoting from the Corum paper concerning self resonance of a coil: "The forward and backward traveling waves have superposed to give this voltage standing wave distribution along the resonator. There is a voltage null at the base, a voltage maximum at the top, and a sine wave envelope along the structure." That defines 90 degrees of coil. For the standing wave, there are 90 degrees between a voltage null and a voltage maximum. The voltage maximum at the top of the coil corresponds to the current null existing there because the current has no place to go. The voltage null at the base corresponds to the current maximum there which is a necessary condition for self resonance. There's 90 degrees between a voltage null and a voltage maximum. There's 90 degrees between a current null and a current maximum. -- 73, Cecil http://www.qsl.net/w5dxp Article: 224040 of rec.radio.amateur.antenna From: "Robert Lay (W9DMK)" Subject: Re: spectral power density Date: Wed, 03 May 2006 12:52:15 -0400 Message-ID: <0qnh529sudqlmqmhq5142s58q9ejo4jhse@4ax.com> References: <1146491265.725531.281770@i39g2000cwa.googlegroups.com> On 1 May 2006 06:47:45 -0700, "electro" wrote: >under unlicensed 2.4GHz FCC part 15 for digital modulation >system(non-spread spectrum), it says that the >1. maximum conducted power is 1W >2. the spectral density be not greater than 8dB for every 3khz band >during continous transmission >3. the 6-dB bandwith is at least 500khz > >question: >1. what is spectral density in this sense and its significance? >2. how can i measure my spectral density? >3. how does 1, 2 and 3 relate to each other? I downloaded the FCC's Part 15 regulations and have concluded: 1) They do say 500 kHz bandwidth 2) They do refer to +8dBm - not 8 dB 3) I agree with Tom's response Article: 224041 of rec.radio.amateur.antenna From: Me Subject: Re: Measuring quarter wave cable length with HP 8405A References: <3omh52p0s8ch01bocrb8l3bgbd2deg5en9@4ax.com> Message-ID: Date: Wed, 03 May 2006 16:52:47 GMT In article <3omh52p0s8ch01bocrb8l3bgbd2deg5en9@4ax.com>, Gary Schafer wrote: > I am using an HP 8405A vector voltmeter to try and measure the delay > in a transmission line in the 2 meter band. > This is part of a phasing harness for a pair of 2 meter antennas to > put them into circular polarization. > > The set up is as follows: A T connector on the signal generator with a > pair of 75 ohm ¼ wave length jumpers from either side of the T. At the > ends I put an adaptor and a bnc T connector of which one side connects > to the probe of the 8405A and the other end of the bnc T is a 50 ohm > load. > The other 75 ohm ¼ wave jumper has the same setup with the bnc T, 50 > ohm load and B channel probe of the 8405A. > > With this I see a zero degree phase difference on the 8405A as it > should be. > Then I insert a ¼ wave length 50 ohm cable between one of the 75 ohm > cable ends and the bnc T connector / 8405A probe connection point. > There are the same number of adaptors in each side of the lines. The > only addition is one barrel connector and the ¼ wave length of 50 ohm > cable. (this is in the B channel by the way) > The additional barrel connector is part of the ¼ wave length on the 50 > ohm line. > > The wanted frequency is 145 Mhz. > Rather than seeing 90 degrees delay with the added 50 ohm line section > I only see 60 degrees of delay?? If I run the frequency up to around > 180 Mhz I get the 90 degrees delay shown on the 8405A. > What do you suppose I am doing wrong in the measurement setup? > > I have measured the delay on the 50 ohm line section by itself (with > the one barrel connector) and I see 90 degrees of delay at 145 Mhz. I > used 20 db pads on each side of the T from the signal generator to > isolate the two sides of the test setup when measuring this cable by > itself. > > Thanks > Gary K4FMX > When you figured the length of the 1/4 wave section, did you account for the Velocity Factor of the cable? Me Article: 224042 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Measuring quarter wave cable length with HP 8405A References: <3omh52p0s8ch01bocrb8l3bgbd2deg5en9@4ax.com> Message-ID: Date: Wed, 03 May 2006 17:18:16 GMT Gary Schafer wrote: > The wanted frequency is 145 Mhz. > Rather than seeing 90 degrees delay with the added 50 ohm line section > I only see 60 degrees of delay?? If I run the frequency up to around > 180 Mhz I get the 90 degrees delay shown on the 8405A. > What do you suppose I am doing wrong in the measurement setup? I don't understand the description of the test setup so this may be a stupid question but what would a 50 ohm SWR meter read if installed in that 50 ohm line during the test? -- 73, Cecil http://www.qsl.net/w5dxp Article: 224043 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Wire diameter vs Impedance References: <1146256136.332525.320580@i39g2000cwa.googlegroups.com> <1146504560.509236.51040@j33g2000cwa.googlegroups.com> <1146507445.103318.321540@j73g2000cwa.googlegroups.com> <1Bs5g.392$fb2.83@newssvr27.news.prodigy.net> <1146528536.568289.29120@g10g2000cwb.googlegroups.com> <93K5g.71838$H71.57495@newssvr13.news.prodigy.com> Message-ID: <7766g.20846$4L1.20063@newssvr11.news.prodigy.com> Date: Wed, 03 May 2006 17:54:11 GMT Dave wrote: > So, the attenuation constant is still a complex number and it is > dimensionless. The attenuation constant is a real number, not a complex number. -- 73, Cecil http://www.qsl.net/w5dxp Article: 224044 of rec.radio.amateur.antenna Date: Wed, 03 May 2006 14:31:12 -0400 From: Dave Subject: Re: Wire diameter vs Impedance References: <1146256136.332525.320580@i39g2000cwa.googlegroups.com> <1146504560.509236.51040@j33g2000cwa.googlegroups.com> <1146507445.103318.321540@j73g2000cwa.googlegroups.com> <1Bs5g.392$fb2.83@newssvr27.news.prodigy.net> <1146528536.568289.29120@g10g2000cwb.googlegroups.com> <93K5g.71838$H71.57495@newssvr13.news.prodigy.com> <7766g.20846$4L1.20063@newssvr11.news.prodigy.com> Message-ID: My error ... I meant propagation constant. Cecil Moore wrote: > Dave wrote: > >> So, the attenuation constant is still a complex number and it is >> dimensionless. > > > The attenuation constant is a real number, not a complex number. Article: 224045 of rec.radio.amateur.antenna From: Butch Magee Subject: Re: 4:1 balun question Date: Wed, 03 May 2006 14:00:07 -0500 Message-ID: <125hvhfq0l5vl7f@corp.supernews.com> References: Mike Coslo wrote: > Anyone here have a good web reference on making a 4:1 balun? I'm looking > for the dual core design, not the single core design. Lots of those to > google. > > Do the single core designs really not work? I had a single core > homebrew that seemed to work, but I'm a tad confused after hearing that > they don't. > > - 73 de Mike KB3EIA - > > Better, easier and probably cheaper to buy what you need from Buxcomm.com Article: 224046 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: A little more on missing degrees References: <44560cd1_2@newsfeed.slurp.net> Message-ID: <4u76g.64848$_S7.5680@newssvr14.news.prodigy.com> Date: Wed, 03 May 2006 19:26:56 GMT Dave wrote: > Where is the other 74 degrees?? Please reference my other postings. It is all explained there. 1. There are tens of degrees in the coil. That phase shift is not instantaneous and obeys the VF of the coil. 2. There are tens of degrees in the impedance discontinuity between the coil and stinger. That phase shift is instantaneous and requires no delay. 3. There are tens of degrees in the stinger. That phase shift is not instantaneous and obeys the VF of the stinger. 4. They all add up to 90 degrees. -- 73, Cecil http://www.qsl.net/w5dxp Article: 224047 of rec.radio.amateur.antenna From: "XaNder" Subject: NewB: antenna and ADC howto Message-ID: <1K76g.18754$TK.18106@tornado.fastwebnet.it> Date: Wed, 3 May 2006 21:43:53 +0200 Hi all, I'm Alexander and I'm a total newbe of radiofrequency comunication. Fortunately I have a little knowledge of physics. Now, my problem is: I want to record a raw UHF signal. First step: I need an antenna. Any suggestion (web HowTos, pdf or anything alike)? Once I have the antenna and the circuitry behind it, I'd need a means of recordingWhen I was at the university we had some nice toys which were able to create (wired) digital signals. No I suppose there also are spectrum analizers which could transform an analogic signal from the antenna to a digital one so it can be easily recorded on a pc. Unfortunately I don't even know how they are called! :-/ I called them ADC (as opposed to DAC), but never heard this term actually. Could you give me a track to follow? Thanks to anyone so kind to help, Alexander Article: 224048 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: A little more on missing degrees Date: Wed, 03 May 2006 13:19:09 -0700 Message-ID: <125i422gjc92dcf@corp.supernews.com> References: <44560cd1_2@newsfeed.slurp.net> Dave wrote: > > Where is the other 74 degrees?? This is the question that started this > 2 month discussion. > > Is there a fallacy in Corum's paper? > > Does Corum's paper apply to a combination of a loading coil and > radiating elements? > > My reasoning is as follows: if I draw a phasor diagram, I have +10 > degrees phase shift from the feed point to the base of the coil. I can > then assume a +90 degree phase shift in the coil, classical inductive > response; then, the 'stinger', from the top of the coil to the tip of > the antenna produces a net -10 degree phase shift from both inductive[+] > and capacitive[-] effects resulting in a net 90 degree phase shift for > the full eight foot antenna. > > Am I being too simplistic? > > I conclude that I have a 16 degree long antenna with a feedpoint > resistance of ~13 ohms [ Rr = ~1.0 ohm and Rloss = ~12 ohms] with zero > ohms reactance [resonant]. [And that the phase shifts stated above are > fundamentally correct.] You don't need to go to anywhere near that much trouble. If you replace the stinger with a lumped series RC to ground with the same impedance as the stinger, you'll get nearly the same currents, both magnitude and phase, at the top and bottom of the coil as you did with the stinger. No "missing degrees" -- no "degrees" at all, in fact. No forward and reverse traveling waves, no standing waves. No smoke and mirrors, no bafflegab. Just plain old circuit analysis. Roy Lewallen, W7EL Article: 224049 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Measuring quarter wave cable length with HP 8405A Date: Wed, 03 May 2006 13:29:59 -0700 Message-ID: <125i4mcgol7vv65@corp.supernews.com> References: <3omh52p0s8ch01bocrb8l3bgbd2deg5en9@4ax.com> Forgive me for asking questions about seemingly obvious things, but something isn't as it appears. If it's really like you've described, the phase difference should be 90 degrees. Please verify that the added 50 ohm quarter wave section is between the end of the 75 ohm line and the 50 ohm terminator/probe connector as you described and not between the signal generator tee and one of the 75 ohm lines. If the latter, you will get something other than 90 degrees of phase shift, although I haven't run the numbers to see what it would be. Are you sure the added quarter wave line is 50 and not 75 ohms? Also, what's the ratio of voltage magnitudes at the two probes? Roy Lewallen, W7EL Gary Schafer wrote: > I am using an HP 8405A vector voltmeter to try and measure the delay > in a transmission line in the 2 meter band. > This is part of a phasing harness for a pair of 2 meter antennas to > put them into circular polarization. > > The set up is as follows: A T connector on the signal generator with a > pair of 75 ohm ¼ wave length jumpers from either side of the T. At the > ends I put an adaptor and a bnc T connector of which one side connects > to the probe of the 8405A and the other end of the bnc T is a 50 ohm > load. > The other 75 ohm ¼ wave jumper has the same setup with the bnc T, 50 > ohm load and B channel probe of the 8405A. > > With this I see a zero degree phase difference on the 8405A as it > should be. > Then I insert a ¼ wave length 50 ohm cable between one of the 75 ohm > cable ends and the bnc T connector / 8405A probe connection point. > There are the same number of adaptors in each side of the lines. The > only addition is one barrel connector and the ¼ wave length of 50 ohm > cable. (this is in the B channel by the way) > The additional barrel connector is part of the ¼ wave length on the 50 > ohm line. > > The wanted frequency is 145 Mhz. > Rather than seeing 90 degrees delay with the added 50 ohm line section > I only see 60 degrees of delay?? If I run the frequency up to around > 180 Mhz I get the 90 degrees delay shown on the 8405A. > What do you suppose I am doing wrong in the measurement setup? > > I have measured the delay on the 50 ohm line section by itself (with > the one barrel connector) and I see 90 degrees of delay at 145 Mhz. I > used 20 db pads on each side of the T from the signal generator to > isolate the two sides of the test setup when measuring this cable by > itself. > > Thanks > Gary K4FMX > Article: 224050 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: A little more on missing degrees References: <44560cd1_2@newsfeed.slurp.net> <125i422gjc92dcf@corp.supernews.com> Message-ID: Date: Wed, 03 May 2006 22:29:31 GMT Roy Lewallen wrote: > You don't need to go to anywhere near that much trouble. If you replace > the stinger with a lumped series RC to ground with the same impedance as > the stinger, you'll get nearly the same currents, both magnitude and > phase, at the top and bottom of the coil as you did with the stinger. No > "missing degrees" -- no "degrees" at all, in fact. No forward and > reverse traveling waves, no standing waves. No understanding of the laws of physics - just 1001 shortcuts and rules of thumb - consistent with the dumbing down of the US educational system and amateur radio. -- 73, Cecil http://www.qsl.net/w5dxp Article: 224051 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Measuring quarter wave cable length with HP 8405A References: <3omh52p0s8ch01bocrb8l3bgbd2deg5en9@4ax.com> <125i4mcgol7vv65@corp.supernews.com> <5dai52dp1ftujkssdqjh8398q2l5gusemr@4ax.com> Message-ID: Date: Wed, 03 May 2006 22:34:25 GMT Gary Schafer wrote: > 180 Mhz = -90 degrees A channel -5dbm B channel -2dbm. > 145 Mhz = -60 degrees A channel -3.5dbm B channel -3dbm Did anyone else notice that 90/60 = 75/50? -- 73, Cecil http://www.qsl.net/w5dxp Article: 224052 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Wire diameter vs Impedance Date: Wed, 03 May 2006 15:55:23 -0700 Message-ID: <125id7656rs2vf3@corp.supernews.com> References: <1146256136.332525.320580@i39g2000cwa.googlegroups.com> <1146504560.509236.51040@j33g2000cwa.googlegroups.com> <1146507445.103318.321540@j73g2000cwa.googlegroups.com> <1Bs5g.392$fb2.83@newssvr27.news.prodigy.net> <1146528536.568289.29120@g10g2000cwb.googlegroups.com> <6eCdnYZlm9BIzMrZnZ2dnUVZ8qudnZ2d@bt.com> <1146596054.095856.75500@g10g2000cwb.googlegroups.com> <125fnnqh54t48a7@corp.supernews.com> <1146636593.492337.13540@y43g2000cwc.googlegroups.com> Here's an interesting quote from S.A. Schelkunoff, "Theory of Antennas of Arbitrary Size and Shape", Proc. of the I.R.E., September, 1941 (footnote 17): "From the point of view developed in this paper there is no difference between 'end effect' and radiation." This is the paper in which Schelkunoff develops his often-quoted approximate equations for antenna feedpoint impedance (the ones including sine and cosine integral -- Si and Ci -- terms). He says, basically, that an antenna acts like a transmission line -- a conical antenna like a constant-Z line and a cylindrical (e.g., wire or tubing) antenna like a variable-Z line -- *except at the ends*. At the ends, modes other than TEM are excited, resulting in radiation, modification of antenna impedance, and modification of current distribution. The radiation, he says, can be modeled as either a terminating impedance or as a distributed impedance (R and L) along the line. You can find an abbreviated version of this explanation in Kraus' _Antennas_. A transmission line is similar to an antenna in only some respects, and assuming they act exactly the same leads to erroneous conclusions. Among the many mistakes made in recent postings is the assumption that a complete reflection takes place from the end of an antenna wire. As Schelkunoff, Kraus, and others explain, this isn't correct. Roy Lewallen, W7EL Article: 224053 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: Wire diameter vs Impedance References: <1146256136.332525.320580@i39g2000cwa.googlegroups.com> <1146504560.509236.51040@j33g2000cwa.googlegroups.com> <1146507445.103318.321540@j73g2000cwa.googlegroups.com> <1Bs5g.392$fb2.83@newssvr27.news.prodigy.net> <1146528536.568289.29120@g10g2000cwb.googlegroups.com> <6eCdnYZlm9BIzMrZnZ2dnUVZ8qudnZ2d@bt.com> <1146596054.095856.75500@g10g2000cwb.googlegroups.com> <125fnnqh54t48a7@corp.supernews.com> <1146636593.492337.13540@y43g2000cwc.googlegroups.com> <125id7656rs2vf3@corp.supernews.com> Message-ID: <5Ia6g.21438$4L1.16339@newssvr11.news.prodigy.com> Date: Wed, 03 May 2006 23:06:41 GMT Roy Lewallen wrote: > A transmission line is similar to an antenna in only some respects, and > assuming they act exactly the same leads to erroneous conclusions. A capacitor and resistor is similar to a stinger in only some respects, and assuming they act exactly the same leads to erroneous conclusions. -- 73, Cecil http://www.qsl.net/w5dxp Article: 224054 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Can you put a ground plane 1/2 wave below the antenna to keep Date: Wed, 03 May 2006 16:11:33 -0700 Message-ID: <125ie59o9r6apa7@corp.supernews.com> References: You would have to create a ground plane that extends many wavelengths >from your antenna. The multiple lobe pattern is produced by reflections >from the ground which are far away -- the lower the angle, the farther >from the antenna. Why don't you just lower the antenna to 1/2 wavelength if that's the pattern you want? Then you'll have just the ground plane you need, the right height below the antenna -- the ground. Roy Lewallen, W7EL Harbin wrote: > Howdy: > When a 1/2 wave vertical is about 1/2 wave off the ground you get > your best radiation pattern without extra lobes, but > if you were to put it on a tower, several wavelengths high, you get > multiple lobes. My question is how can you > keep a clean radiation pattern when you are several wavelengths high > with a 1/2 wave antenna? Can you put a ground > plane 1/2 wave below the antenna to keep the clean pattern? > > -- > SeeYaa:) Harbin Osteen KG6URO Article: 224055 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: measuring impedance - I and V phase, or forward and reflected Date: Wed, 03 May 2006 20:11:30 -0700 Message-ID: <125is77pnh2atd9@corp.supernews.com> References: <-IKdnQYQp4968cTZRVn-iA@comcast.com> dansawyeror wrote: > All, > > What is the best way to base impedance measurements, by voltage and > current phase or by forward and reflected power? Measurement or calculation of forward and reverse power don't give you enough information to determine impedance. There are an infinite number of impedances which result in any given set of forward and reverse powers. Likewise, voltage and current phase don't provide enough information. Again, there are an infinite number of impedances possible for any set of voltage and current phases. > First I assume both methods provide the data to measure impedance. No, neither one does. Among adequate sets of measurements which will allow you to determine impedance are both magnitude and phase of both voltage and current; or the ratio of voltage and current and the difference between their phase angles; or the magnitude and angle of the reflection coefficient. > It would seem that both suffer from the real effects of the taking the > measurement. Measuring voltage suffers from the effects of the reflected > signal, I would assume current does as well. Couplers have a built in > cross talk parameter. It's much more difficult than most people realize to make accurate RF measurements. Any measurements have numerous potential sources of error. If you need accurate results, you should always measure a number of known impedances approximately equal to the measurement being questioned to verify that the system is sound. Measuring antennas brings the additional problems of coupling among the antenna, test equipment, and you; disturbances from other signals being received by the antenna; common mode currents; and properties of connecting feedlines. Roy Lewallen, W7EL Article: 224056 of rec.radio.amateur.antenna From: Buck Subject: Re: Can you put a ground plane 1/2 wave below the antenna to keep the clean pattern? Message-ID: References: Date: Wed, 03 May 2006 23:15:11 -0400 On Wed, 3 May 2006 14:51:05 -0700, "Harbin" wrote: >Howdy: > When a 1/2 wave vertical is about 1/2 wave off the ground you get your best radiation pattern without extra lobes, but >if you were to put it on a tower, several wavelengths high, you get multiple lobes. My question is how can you >keep a clean radiation pattern when you are several wavelengths high with a 1/2 wave antenna? Can you put a ground >plane 1/2 wave below the antenna to keep the clean pattern? create a half-wave dipole and mount it vertically. buck n4pgw -- 73 for now Buck N4PGW Article: 224057 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: Measuring quarter wave cable length with HP 8405A Date: Wed, 03 May 2006 20:46:06 -0700 Message-ID: <125iu83jl4b2f3f@corp.supernews.com> References: <3omh52p0s8ch01bocrb8l3bgbd2deg5en9@4ax.com> <125i4mcgol7vv65@corp.supernews.com> <5dai52dp1ftujkssdqjh8398q2l5gusemr@4ax.com> Gary Schafer wrote: > . . . > The length of the 50 ohm line is 9 ¾" from shielded area to shielded > area (not counting the center pin exposed when shell is pulled back). > With the barrel installed it makes it 10 ¾" in length that is > shielded. > . . . By my reckoning, a free space quarter wavelength at 145 MHz is 20.335 inches. Assuming solid polyethylene dielectric coax, this would be about 13.4 inches of coax. 10-3/4 inches would be about 72 degrees. The probes have a shunt C of 2.5 pF, resulting in a Z (-X) of about 440 ohms at 145 MHz, not 100k ohms. If you parallel that with 50 ohms and terminate a 72 degree 50 ohm cable with it, the voltage delay in the cable is 78 degrees -- that is, the imperfect termination actually increases the cable delay by 6 degrees. If the cable Z0 is 45 ohms instead of 50, the delay is a couple of degrees less with that load; if it's 55 ohms, the delay is a couple of degrees more. Maybe your 50 ohm termination isn't quite what you think it is -- as you can see, it doesn't take much to substantially change the cable's delay. As I've said often, most people don't realize how difficult it is to make accurate RF measurements. Roy Lewallen, W7EL Article: 224058 of rec.radio.amateur.antenna From: Allisonnospam@nouce.bellatlantic.net Subject: Re: FCC regulation on max. antenna tower height @ 2.4GHz ??? Message-ID: References: <1146737737.626050.144830@v46g2000cwv.googlegroups.com> Date: Thu, 04 May 2006 12:32:28 GMT On 4 May 2006 03:15:37 -0700, "electro" wrote: >what is the maximum limit for antenna tower @ 2.4ghz ISM band?any link >you know that leads to this regulation? or only the FAA authorizes such >height regulations? > >thanks For towers over 200ft and within a specific distances to an airport there are rules (both FAA and FCC). There may be other restrictions but not specific to only 2.4ghz ISM and local codes are more often an issue than federal codes. Allison Article: 224059 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: measuring impedance - I and V phase, or forward and reflected References: <-IKdnQYQp4968cTZRVn-iA@comcast.com> Message-ID: Date: Thu, 04 May 2006 12:48:28 GMT dansawyeror wrote: > What is the best way to base impedance measurements, by voltage and > current phase or by forward and reflected power? > It would seem that both suffer from the real effects of the taking the > measurement. Measuring voltage suffers from the effects of the reflected > signal, I would assume current does as well. Couplers have a built in > cross talk parameter. If in a transmission line where the Z0 is known, either method will give valid results within a certain accuracy. A bridge circuit would probably yield the most accurate measurement. -- 73, Cecil http://www.qsl.net/w5dxp Article: 224060 of rec.radio.amateur.antenna From: Cecil Moore Subject: Re: 4:1 balun question References: Message-ID: Date: Thu, 04 May 2006 13:19:29 GMT Dan Richardson wrote: > Did you read the article Cecil? He place the current balun/choke on > the opposite side. Looked like an interesting approach. Yes, I'm wondering if things would change if the positions were reversed? How does that choke perform when it sees 2000 + j1000 ohms? -- 73, Cecil http://www.qsl.net/w5dxp Article: 224061 of rec.radio.amateur.antenna From: gsm@mendelson.com (Geoffrey S. Mendelson) Subject: Re: FCC regulation on max. antenna tower height @ 2.4GHz ??? Date: Thu, 4 May 2006 13:21:05 +0000 (UTC) Message-ID: References: <1146737737.626050.144830@v46g2000cwv.googlegroups.com> Allisonnospam@nouce.bellatlantic.net wrote: > There may be other restrictions but not specific to only 2.4ghz ISM > and local codes are more often an issue than federal codes. It is also important to check the terms of your license. In the U.S. 2.4gHz is shared between amateur (Ham), ISM (industrial, scientific and medical) and unlicensed users. Each has it's own terms and conditions. For example, the infamous Pringles can antenna was designed and used by an FBI agent in the course of an investigation. It may not have been legal for use by regular unlicensed WiFi users. Geoff. -- Geoffrey S. Mendelson, Jerusalem, Israel gsm@mendelson.com N3OWJ/4X1GM IL Voice: (07)-7424-1667 IL Fax: 972-2-648-1443 U.S. Voice: 1-215-821-1838 Visit my 'blog at http://geoffstechno.livejournal.com/ Article: 224062 of rec.radio.amateur.antenna From: "Tom Donaly" Subject: Re: May 1st 2006, Civil War Begins References: <1146730693.889876.75440@j73g2000cwa.googlegroups.com> Message-ID: Date: Thu, 04 May 2006 13:51:04 GMT nm5k@wt.net wrote: >>May 1st 2006, Civil War Begins .. > > > LOL, that'll be the day... is this related to "missing degrees" ? > I guess we missed the civil war down here in Texas. May 1 > came and went, and I didn't notice anything irregular at all. > Nothing was hampered, and it is still quite warm here too.. > MK > Nothing happened here in California, either, except that a lot of immigrants had a nice march and got to listen to some inspirational speeches. Afterwords, they all went back to work. 73, Tom Donaly, KA6RUH Article: 224063 of rec.radio.amateur.antenna From: "Cecil Moore" References: Subject: Re: 4:1 balun question Message-ID: Date: Thu, 04 May 2006 15:33:59 GMT "Reg Edwards" wrote: > When it sees 2000 + j1000 ohms there's hardly any current to choke > anyway. Yes, but how much current is there 3/8WL back from that point? -- 73, Cecil, W5DXP Article: 224064 of rec.radio.amateur.antenna From: "Cecil Moore" References: Subject: Re: 4:1 balun question Message-ID: <7eq6g.1670$fb2.1060@newssvr27.news.prodigy.net> Date: Thu, 04 May 2006 16:46:59 GMT "Reg Edwards" wrote: > W5DXP wrote: > > Yes, but how much current is there 3/8WL back from that point? > Isn't that where you should be placing the choke? Kinda hard to do if the feedline is ladder-line. Maybe a more logical thing to do is to increase the length of the ladder-line until a current maximum point is available at the coax/ladder-line junction. -- 73, Cecil, W5DXP Article: 224065 of rec.radio.amateur.antenna From: Roy Lewallen Subject: Re: measuring impedance - I and V phase, or forward and reflected Date: Thu, 04 May 2006 11:49:37 -0700 Message-ID: <125kj69ov8qqfc4@corp.supernews.com> References: <-IKdnQYQp4968cTZRVn-iA@comcast.com> <125is77pnh2atd9@corp.supernews.com> <4459FB68.2080502@comcast.net> Thanks for the clarification. The HP4805a isn't an impedance meter. It's a vector voltmeter, which measures voltage amplitude and phase. As you know, it requires external directional couplers to measure impedance. (Or you could use current measurements using current probes in addition to the voltage measurements.) When you use directional couplers with the vector voltmeter -- or with a network analyzer for that matter -- you're not measuring forward and reflected power. You're measuring forward and reflected voltage. As I mentioned in my last posting, power measurement doesn't give you enough information to determine impedance. The answer to your question is that you can't measure impedance at all using only the voltage probes of the 4805a, and you can't measure it at all by measuring forward and reverse power with directional couplers. If you want to compare using voltage *and current* probes with measuring forward and reverse *voltages* with directional couplers, the former is probably better when impedances are considerably different than 50 ohms resistive, the latter better in a near 50 ohm system. Making accurate measurements with either method is much more difficult than most people realize, and it helps to have an understanding of what you're actually measuring. Both methods have numerous sources of possible error which have to be understood and controlled. Roy Lewallen, W7EL Network dansawyeror wrote: > Roy, > > Thank you. Yes, I understood both magnitude and phase are required for > both. > > The question arose after looking into the block diagram of an HP 4805a > Impedance Meter. It measures voltage and current as the basis for > determining impedance. > > My work with a vector voltmeter has been through using directional > couplers and measuring forward and reflected power. > > My question is: Is there an inherent accuracy benefit to one measurement > basis over the other? > > Or: Are current and voltage probes inherently easier to build and more > accurate then directional couplers? > > - Dan > > > Roy Lewallen wrote: >> dansawyeror wrote: >> >>> All, >>> >>> What is the best way to base impedance measurements, by voltage and >>> current phase or by forward and reflected power? >> >> >> Measurement or calculation of forward and reverse power don't give you >> enough information to determine impedance. There are an infinite >> number of impedances which result in any given set of forward and >> reverse powers. >> >> Likewise, voltage and current phase don't provide enough information. >> Again, there are an infinite number of impedances possible for any set >> of voltage and current phases. >> >>> First I assume both methods provide the data to measure impedance. >> >> >> No, neither one does. Among adequate sets of measurements which will >> allow you to determine impedance are both magnitude and phase of both >> voltage and current; or the ratio of voltage and current and the >> difference between their phase angles; or the magnitude and angle of >> the reflection coefficient. >> >>> It would seem that both suffer from the real effects of the taking >>> the measurement. Measuring voltage suffers from the effects of the >>> reflected signal, I would assume current does as well. Couplers have >>> a built in cross talk parameter. >> >> >> It's much more difficult than most people realize to make accurate RF >> measurements. Any measurements have numerous potential sources of >> error. If you need accurate results, you should always measure a >> number of known impedances approximately equal to the measurement >> being questioned to verify that the system is sound. Measuring >> antennas brings the additional problems of coupling among the antenna, >> test equipment, and you; disturbances from other signals being >> received by the antenna; common mode currents; and properties of >> connecting feedlines. >> >> Roy Lewallen, W7EL Article: 224066 of rec.radio.amateur.antenna From: Michael Coslo Subject: Re: Plastic Antenna Insulators Date: Thu, 04 May 2006 17:00:46 -0400 Message-ID: References: <8J-dnfyFU-D-w8jZnZ2dnUVZ_tOdnZ2d@adelphia.com> Dave Heil wrote: > Mike Coslo wrote: >> Dave Heil wrote: >>> Highland Ham wrote: >>> ========================= >>> >>>> To be UV resistant the plastic should be black ,eg it contains >>>> carbon black ( like soot) If ,in general, plastic material is >>>> exposed to sun light it deteriorates over time (especially when >>>> pigments are involved). >>>> Example: coloured polypropylene rope . >>>> If that material would be black ,it would have a very long life. >>>> But then the sales of this material would decline ;)), hence you >>>> only find coloured polypropylene rope ,blue ,orange ,red , yellow >>>> ,etc ,at least in the UK. >>>> >>>> Here in the north of Scotland (no sun in abundance) I use >>>> (blue)polypropylene guys on a 13m (40ft)mast ,which have to be >>>> replaced every 7 -8 years .But it is cheap. >>> >>> >>> I question that 7-8 year figure. Some Finnish friends put up a >>> "temporary" tower with a tribander at the OH0Z site in the 1990s. >>> They used new polypropylene ski rope. I went out one weekend and >>> there lay the tower and tribander, victims of a guy rope failure. >>> I'd NEVER use the stuff for guying or antenna supports. >> >> >> I've not found the polyester stuff to be very good either. I >> wonder if that stuff lasting for 7 years might be something else? > > Polyester or polypropylene? The polyester is pretty good even without > the black UV resistant layer. Polypropylene frizzes, fades and gets > weak very, very quickly. > >>>> Polyester rope as used on sailing boats is UV resistant (even >>>> without carbon black) and would last 30+ years ,but it is relatively >>>> expensive. >>> >>> >>> Polyester is excellent material. There is a polyester rope sold >>> under the "Synthetic Textiles" name here in the U.S. which is simply >>> great. >>> It is braided, not twisted. The inner core is white. There is an >>> outer braid which is black. I have some which is fourteen years >>> old. It is still strong and flexible. I've seen it. I might just pt my next antenna up with it. >> Does it have much stretch? I'm looking for something new after >> replacing my dipole the third time since January..... > > One of the very good things about polyester rope is that it doesn't > stretch much at all--let's say, compared to nylon rope which stretches a > great deal. Where I am at, we get some pretty strong and gusty winds the past few years. The trees can get whipping in different directions fairly often. My old nylon string would stretch, and could even support my weight (don't ask how I know that) My thoughts are that iff I put up something that doesn't have a little give, the stress is just going to transfer from the line to the antenna. At that point I'd start breaking the antenna. > Where is your rope breaking and what is it attached to? I use plain old > nylon 1/4" rope to support the end of my inverted L for 160m. The far > end runs though a nylon pulley attached to another rope up in a maple > tree. The rope attached to the antenna runs down the tree and is > attached to an old window sash weight. The weight is free to bob up and > down with the swaying of the tree. That keeps the rope and antenna wire > from breaking. Nothing so complex. I have some line running through a grook in the limbs. The failure point for the old stuff I was using was at the rub point. Now it seems almost random. Your method would probably be a lot better for me to use. >>>> Plastic antenna insulators (sold in the UK ) are usually black , so >>>> are the outdoor balun enclosures and plastic insulators on Yagi >>>> antennes. >>> >>> >>> We're now seeing some white plastic insulators here. I tried some in >>> the sun of Africa. They looked like they were pitted and >>> deteriorating after three years in the sun of Botswana. I either use >>> ceramics or make my own out of 1/2" thick clear plexiglass sheet or >>> 3/4" plexi rod. That yellows but doesn't otherwise seem to deteriorate. >> >> >> I've been using black plastic eggs sold for electric fencing apps. >> They've worked well for about 5 years now. > > They're likely a little short for high power, Mike. You might consider > using a couple of them at each end with a short piece of nylon rope in > between them. I use the black plastic "nail-on" fence insulators for > running a beverage antenna down a tree line. They are cheap and they > work well. The have a snap-in retainer so they're easy to re-use if the > aluminum fence wire I'm using should ever break. > > I use those Hy-Gain center insulators made of black plastic with rubber > membrane and stainless screws and nuts. They never seem to fail and > certainly keep water out of the coaxial cable. Ten-Tec is making their > little Acro-Bat center insulator. It is good for 300 ohm window line > and RG-58 but they don't make a model for RG-213-sized cable. Once again, sounds like a setup I might want to emulate. Thanks, Dave. - 73 de Mike KB3EIA - Article: 224067 of rec.radio.amateur.antenna From: XaNder Subject: Re: NewB: antenna and ADC howto References: <1K76g.18754$TK.18106@tornado.fastwebnet.it> <1146687006.485441.17900@j73g2000cwa.googlegroups.com> Message-ID: Date: Thu, 04 May 2006 23:39:47 +0200 First of all thanks for your answer. K7ITM wrote: > The antenna you pick should depend on just what you are trying to > receive. Could you give us any more info? I have to be able to read an UHF signal produced by an ISO-18000/6 (not B version) RFID reader/tag signal. I first thought to directly use the tag's antenna itself but have no idea of how to connect it to a sampler. Plus it uses backscatter asa means of communication and don't know how this influences any signal at the end of the antenna. > As for digitizing the signal, yes, you can actually buy receivers with > digital output, though good ones tend to be expensive. Well, we are a research lab. Sooner or later I think we'll get our hands on something if it's actually usefull and we ask for it. Nevertheless it has to be as cheap as suitable. --Inline Edit--: I have to ask our providers if they have any passive reader they won't miss ;-) . > If you want > very broadband digitization, you can get ADCs that sample at 10^9 > samples/second and above, but only to about 8 bits of resolution, and > accuracy even less than that. If you want to digitize only a > relatively narrow band, you can use analog techniques to convert the > signal to a lower frequency, or you can use an ADC that is capable of > "undersampling" -- accurately sampling a signal at a frequency above > half its sampling frequency. In either case, you need filters to > insure that the band of frequencies you let through doesn't cause > "aliasing". > (You should be able to find plenty on that with a web search.) Thanks, I'll go and search as I don't remember very well. The band is as narrow as 70MHz if I'm not mistaking. Take a look at http://zone.ni.com/devzone/conceptd.nsf/webmain/1622E8ED427AA28C8625714D0067926D As I told you I'm a total noob and I don't even know if there's only a channel or more (though I think there's only 1) > Anyway, there are some key questions: what signals do you > want to receive, and what bandwidth do you want to digitize? Well, there are lots of RFID protocols out there, but as this is our first test I think we should do simple things. That's why I chose this protocol (it should be simple (yet very complicated for me!) compared to the ISO 18000/6B).Do you think this should be easier in HF (125/130kHz) or VHF (13.56MHz) domain (we have any kind of readers:-). > Do you > want to be able to adjust the center frequency of the band you > digitize, or will it be fixed? What dynamic range do you need? What > amount of noise in the receiver can you tolerate? I'm not really a guru of telecom. The only thing I can say is that the S/N ratio is *probably* no problem to me ... just get the reciever closer to the emitter and I *think* it would be ok. Correct me if I say any nonsense. > Without answers to > these basic questions and some others, you probably won't get the > results you seek. On the back end, another question is, what will you > do with the data? Can you record it or process it real-time without > choking on it? No real-time processing. At least for now and a good deal of time from now. I first have to understand how this works. Plus once it's sampled I can do all the tests I need to. > And finally, are you looking to buy a system, or build > one, or some combination? It depends on how much time would cost (or how much money...). Cheers and thanks again, Alexander From Thu May 4 22:33:03 EDT 2006 Article: 224068 of rec.radio.amateur.antenna NNTP-Posting-Date: Thu, 04 May 2006 19:37:30 -0500 From: Dan Richardson <> Newsgroups: rec.radio.amateur.antenna Subject: Re: J pole question Date: Thu, 04 May 2006 17:37:14 -0700 Message-ID: References: X-Newsreader: Forte Agent 1.93/32.576 English (American) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 23 NNTP-Posting-Host: 68.64.59.124 X-Trace: sv3-WYxW9hVYLWG9wzbiCgCfYK+D2YrRJAQcYmO+jyGYmZAIHCHLnVxGxPRYiHSJ1MmvuuFiGpgiIfWJfnA!gQGtHQTI1M2P9ZRZ4oneFF08UAASxnP/NQnPCCHN6pt7RULKbzpd5YpvY9uG2LpsHQ8Aig7DrI5E!SThHs40LcBi2QPkX5Zmb X-Complaints-To: abuse@adelphia.net X-DMCA-Comp