Subject: GLOWBUGS digest 269

From: [email-masked]
Date: Thu, 22 Aug 1996 22:32:26 -0500 (CDT)

GLOWBUGS Digest 269

Topics covered in this issue include:

  1) Thanks: Dial for Regen
	by Terry Dobler  KJ7F <[email-masked]>
  2) Crystal set article -- 70s Pop Sci needed
	by Andy Wallace <[email-masked]>
  3) Re: And Terry Said.....
	by [email-masked]
  4) "Pi" vs. "T" Matching Net
	by "James P. Rybak" <[email-masked]>
  5) Re: "Pi" vs. "T" Matching Net
	by Steve Ellington <[email-masked]>
  6) Re: "Pi" vs. "T"
	by [email-masked] (Jim Haynes)
  7) Re: those big, smooth dials......
	by [email-masked] (Tom R. Rice)
  8) Re: "Pi" vs. "T"
	by "Peter C. Wotherspoon" <[email-masked]>
  9) Re: "Pi" vs. "T"
	by [email-masked]
 10) Dan's Small Parts
	by "Terry L. Dobler" <[email-masked]>

----------------------------------------------------------------------

Date: Wed, 21 Aug 96 23:38 MDT
From: Terry Dobler  KJ7F <[email-masked]>
To: [email-masked]
Subject: Thanks: Dial for Regen
Message-ID: <[email-masked]>

   Thanks to all who replied to my post.   I am following up on all
the leads.   What a nice place Glowbugs is.

   On the idea of using old CD's.   Very interesting.   Even if I
don't use it on this project I'm sure I will use it sometime.   I
even have a few of the writeable CD's from a project we did at
work.   They are a beautiful gold color.   Perhaps the markings
could be printed on clear sheets like those for overhead projectors
and either transfered or laminated onto the CD?

   I downloaded the circular.zip file and printed it out.   My hats
of to NA4G for a super job.   I'll check out the rest of the files
as time permits.

Terry  KJ7F

[email-masked]  (Boise, Idaho)  http://netnow.micron.net/~kj7f

------------------------------

Date: Thu, 22 Aug 96 08:11:41 EDT
From: Andy Wallace <[email-masked]>
To: [email-masked]
Subject: Crystal set article -- 70s Pop Sci needed
Message-ID: <9608221211.AA00770@taku>

Hi, folks!

Years ago I built a diode crystal set and it
was super...coil was wound on a Diamond Crystal
salt box. Selective and sensitive -- worked great
until I found a "better" coil form and put it
on a nicer board. :-/

I know I have an issue of Popular Science with that
article laying around, but after several moves I
can't find the darn thing. 

I know it was from 77 thru 79, don't remember what
the cover looked like, but the article title was
BUILD AN OLD-TIME CRYSTAL SET. Early 77 sticks in my 
mind. 

Hope the sacrilege of wanting a silicon diode circuit
doesn't spoil the glowbugs list :-) but in
the spirit of homebrewing an ancient circuit 
I thought I'd ask. All I really need is the
coil data. 

Of course if the issue turns up I will be glad to 
make copies or scan it in or something!

73,
--Andy
[email-masked]

------------------------------

Date: Thu, 22 Aug 1996 10:11:45 -0400 (EDT)
From: [email-masked]
To: [email-masked]
Cc: [email-masked] (), [email-masked]
Subject: Re: And Terry Said.....
Message-ID: <[email-masked]>

> 
>    Thanks to all who replied to my post.   I am following up on all
> the leads.   What a nice place Glowbugs is.

Ye knows, mateys, a fine place de ol' Globuggin' hangout it be!
Kudos to all ye fine fellers!

>    On the idea of using old CD's.   Very interesting. 

Continuing the thread, for the sake of discussion.....

Anyone got any ideas about building rim-driven drives (like the dials
on the old Hammarlund receivers using white plastic circular dials
driven by a squeeze roller)?  I like the idea of a regen with a very
fine slow speed rim driven drive about 12 inches in diameter, with
a fine 0-100 scale of some sort, maybe of black imitation bakelite
with white graduations typical of 20's sets or aluminum with black
graduations typical of 10's sets and 30's sets.  Genrad used to make
a magnificent engine cut dial scale about 12 inches in diameter that
was rim driven and had a magnifying glass to read the fine divisions
to one part in 1000.  That would make one classy regenerator dial!

What comes to mind is something like:

1.  cut a circular aluminum plate of appropriate diameter.
    mount on a shaft with a bushing made from an old potentiometer
    housing, and mount the capacitor for tuning way back from
    the front panel on a second subpanel or plate for stability.

2.  use an old potentiometer housing shaft and bearing for the
    drive bushing and shaft.

3.  use a model airplane rubber wheel or a rubber wheel off an old
    recorder capstan or something like that as the drive wheel.

4.  wobble the hole that mounts the shaft bearing bushing so that it
    can wobble a bit to maintain tension on the dial wheel, then
    spring load the drive wheel onto the dial plate.

What have you done in a similar manner?

Bob/NA4G

------------------------------

Date: Thu, 22 Aug 1996 08:34:59 -0600 (MDT)
From: "James P. Rybak" <[email-masked]>
To: Glowbugs <[email-masked]>
Subject: "Pi" vs. "T" Matching Net
Message-ID: <[email-masked]>

Can anyone tell me if there is any particular advantage (or disadvantage) 
over choosing a "Pi" over a "T" matching network, or vice versa, for use 
as an antenna matching circuit?  Most tuners seem to use the "Pi" 
configuration.  Is that because the "Pi" net is easier/better to use or 
is it because of some other factor?

Thanks.

Jim Rybak  W0KSD

------------------------------

Date: Thu, 22 Aug 1996 10:58:58 -0400 (EDT)
From: Steve Ellington <[email-masked]>
To: "James P. Rybak" <[email-masked]>
Subject: Re: "Pi" vs. "T" Matching Net
Message-ID: <Pine.GSO.3.93.960822105050.16246A-100000@iglou>

One advantage of the T network is that if you use a roller inductor, it
allows you to physically ground the roller and drive shaft. The Pi's
roller inductor must be floating and would require total isolation from
ground. However, I believe there are some trade-offs as to efficiency.
Seems like I recently read an article in QST which compared various
antenna matching boxes. The T network version were the most lossy while
the old boatanchor Johnson and Collins units has the least amout of loss.
And we're talking significant loss to the tune of 20% in some tuners they
tested. 

Steve Ellington [email-masked]  Louisville, Ky 

------------------------------

Date: Thu, 22 Aug 1996 09:44:01 -0700
From: [email-masked] (Jim Haynes)
To: [email-masked]
Subject: Re: "Pi" vs. "T"
Message-ID: <[email-masked]>

Another factor is that the pi network has the configuration of a low-pass
filter; hence it attenuates harmonics.  I recall that the pi network
became popular in the time frame when the cancer of TV was spreading
across the face of the land.

------------------------------

Date: Thu, 22 Aug 1996 10:02:48 -0700 (PDT)
From: [email-masked] (Tom R. Rice)
To: [email-masked] (glowbugs)
Subject: Re: those big, smooth dials......
Message-ID: <[email-masked]>

> 
> What have you done in a similar manner?

	Well, I'm fortunate in having a few of the real Velvet
	Vernier dials in stock, but somehow the lust for smooth,
	pretty dials is never satisfied.  The National ODD dial
	drive was a neat little pinch drive to be applied to
	the plain-jane brass disk dials such as the O or the
	K types.  So I think the approach of making a big disk
	is the way to go, but the problem will be making a smooth
	pincher drive.  I've not had much success with a straight
	rubber rim-drive roller.  

	Note that precision machine part houses such as PIC and
	W. Berg sell beautiful engraved dials up to four inches
	in diameter;  they're not cheap, but they're sure pretty!

	My problem is less the mechanical end, but the hassle of
	making really nice engraving/printing/whatever markings
	on the dial.   Suggestions are appreciated......

	73 de WB6BYH  

-- 
"Start off every day with a smile and get it over with."  --W.C.Fields
Tom R. Rice  
[email-masked]     
CIS: 71160,1122       

------------------------------

Date: Thu, 22 Aug 1996 13:35:22 -0400 (EDT)
From: "Peter C. Wotherspoon" <[email-masked]>
To: Jim Haynes <[email-masked]>
Subject: Re: "Pi" vs. "T"
Message-ID: <[email-masked]>

Right on!

On Thu, 22 Aug 1996, Jim Haynes wrote:

> 
> Another factor is that the pi network has the configuration of a low-pass
> filter; hence it attenuates harmonics.  I recall that the pi network
> became popular in the time frame when the cancer of TV was spreading
> across the face of the land.
> 

------------------------------

Date: Thu, 22 Aug 1996 14:04:47 -0400 (EDT)
From: [email-masked]
To: [email-masked]
Cc: [email-masked] (), [email-masked]
Subject: Re: "Pi" vs. "T"
Message-ID: <[email-masked]>

> 
> Another factor is that the pi network has the configuration of a low-pass
> filter; hence it attenuates harmonics.  I recall that the pi network
> became popular in the time frame when the cancer of TV was spreading
> across the face of the land.
> 

A scourge across the land that TV it were.....

Actually, Arthur Collins of Collins Radio fame designed the Pi-network
back in 1930 or so, and it was published in QST about that time.
Memory greymatters tell me it was in 1933 or 1934 maybe in May.
I forget the issue right off, but others should know offhand.
It never really took off in ham use until after the war tho.
It was used in commercial applications before the war, in military
applications during the war (most notably in the ART-13 designed by
Collins), and then after the war in the Collins ham rigs and elsewhere
like a firestorm.  It actually works pretty well, but in modern usage
a Pi-L is probably a better system, or better still, a Pi-L+series-C
for ultimate harmonic rejection and antenna tuning all in one.  The
extreme is the M (Pi+Pi) or M+L+series-C, but it is rarely used in ham gear.

As an antenna matching device the Pi-net quite flexible, much more so
than a standard T style configuration (which is very prone to harmonic
passing).

A good Pi-net should attenuate 30 or so db, while a Pi-L should give
about 40, and the M about 50 (although my rules-of-thumb-numbers may
be a bit off the theoretical or practical attainments).  Memory tells
me the T is about 10-15 db attenuation or not much.

On a homebrew glowbottleburner, I would opt for a Pi-L if I were
using a Pi-net tank or a standard LC tank loosecoupled to a second
tank with a Pi-net taken off a tap on the second tank coil.
But, since I do a lot of breadboarding, and shielding may be secondary,
then the plain Pi-net with series-C is about as good as it will get.

73/ZUT DE NA4G/Bob

p.s. I must have missed the original posting and if this is away off
     topic, then circulate to the bit bucket.....(:+}}.....

------------------------------

Date: Thu, 22 Aug 1996 13:15:51 -0600
From: "Terry L. Dobler" <[email-masked]>
To: [email-masked]
Subject: Dan's Small Parts
Message-ID: <[email-masked]>

   I called Dan of (Dan's Small Parts) today and he has a site 
on the Web.   His catalog may be accessed at ... 
  
   http:\\www.fix.net/dans.html

Terry  KJ7F

------------------------------

End of GLOWBUGS Digest 269
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