Subject: GLOWBUGS digest 252

From: [email-masked]
Date: Sat, 3 Aug 1996 17:56:34 -0500 (CDT)

GLOWBUGS Digest 252

Topics covered in this issue include:

  1) Antioxidant Paste for Aluminum
	by "Barry L. Ornitz" <[email-masked]>
  2) Help!
	by Old Man <[email-masked]>
  3) Re: VFO drift and differential caps
	by [email-masked] (Bill Turner)

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Date: Fri, 2 Aug 1996 21:14:00 -0400 (EDT)
From: "Barry L. Ornitz" <[email-masked]>
To: Boatanchors <[email-masked]>,
Cc: "Rhett T. George" <[email-masked]>
Subject: Antioxidant Paste for Aluminum
Message-ID: <[email-masked]>

Rhett George wrote:

> Please be reminded that there is an anti-oxidant jelly available in
> the electrical supplies area of most hardware stores for improving 
> the connection between Al cable and Cu lugs.  I'll check it out for
> use in Al boatanchor chassis and let you know.

Please do not do this.  The paste (NOALOX and others) is basically a
suspension of fine zinc particles in an organic binder.  It is for
aluminum to aluminum connections ONLY where the sharp (and hard) zinc
particles pierce through the aluminum oxide layer to improve electrical
connections.  The zinc is fairly compatible with the aluminum
electrochemically.  Adding copper to the connection will cause the
aluminum to preferentially corrode in the presence of moisture. 

The correct thing to do, as Bobbi Barmore said, is use toothed lockwashers
with adequate torque to insure the teeth cut through the aluminum oxide
layer and that the fit is essentially air tight.  In the long run, this
joint will still corrode but not nearly as quickly.  In spite of the old
practice of running a ground bus through all lugs, I would not recommend
this.  Any lug not grounded properly is asking for an instability with
ground loops. 

Evidently the electrical supply houses have been promoting NOALOX and such
for copper to aluminum joints but the manufacturers recommendations are
for aluminum to aluminum only. 

		73,  Barry L. Ornitz  WA4VZQ  [email-masked]

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Date: 02 Aug 96 23:02:47 EDT
From: Old Man <[email-masked]>
To: Multiple recipients of l <[email-masked]>
Subject: Help!
Message-ID: <[email-masked]>

	I need the commands to change my e-mail address for the GLOWBUGS
messages.
Can anyone (or the listowner, if he's monitoring things!) let me know.
73,
Sandy W5TVW
new address: [email-masked]

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Date: Sat, 03 Aug 1996 14:16:50 GMT
From: [email-masked] (Bill Turner)
To: [email-masked]
Cc: Multiple recipients of list <[email-masked]>
Subject: Re: VFO drift and differential caps
Message-ID: <[email-masked]>

On Fri, 2 Aug 1996 15:50:36 -0500 (CDT), you wrote:

>Hi gang--
>
>I bought one of those tube-era SSB manuals that ARRL used to publish at the
>recent Flagstaff hamfest, and spent a nice planeride cruising through it
>last week.  I saw a circuit in one of the transceiver projects that I had
>seen before but not understood--and once I understood it, definitely had the
>Oh-Wow! effect in spades.
>
>It's a means of adjusting for VFO drift.  You put a compound capacitance in
>parallel with your main tuning cap.  This compound capacitance consists of
>an NPO cap in series with a differential variable cap. Each of the split
>stator sections of the differential is further in series with a cap.  One
>section goes to an N750 compensating cap, and the other to an NPO cap of
>equal value.
<snip>
---------------------------------------------
There is one catch, which is the same catch all temperature compensation
schemes have:  you must locate the capacitors at a physical location where
their capacitance change will be exactly equal and opposite to whatever is
causing the drift in the first place.  Not easy, but possible in theory at
least.

In fact, you don't need a differential capacitor to do this.  Just use two
separate (ordinary) variables and adjust them one at a time.  Turn variable A
a certain amount, then turn variable B until the frequency comes back to what
it was before turning A.  Then wait and see.

A simpler way to achieve vfo stability is to use a very low-powered oscillator
and let it run 24 hours a day.  A JFET Hartley-type is simple to build and
works fine.  I used one in a 40 meter mobile rig I built some years ago and
never had a trace of drift.  Of course, it needs to be thermally isolated from
the rest of the unit. 
73, Bill W7LZP
[email-masked]

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End of GLOWBUGS Digest 252
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