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Date: Mon, 28 May 2001 20:07:55 -0700
From: alta <alta at alta-research.com>
Subject: [Elecraft] K1 Desert Operation, freq drift management

I just got back from a week of airplane camping at Spencer Hot Springs, an 
unimproved hot springs in a central Nevada desert area.  Temperatures varied 
between 40 and 100 F.  I operated the K1 every day and night.

Previous to this I had had some frequency drift problems with the K1.  It's a 
long story, but the 6v regulator was temp sensitive and subsequently 
replaced.  I also learned from Elecraft that all the caps are chosen to 
offset the drift of the VFO coil and other components in the VFO circuit.  
For example, the poly caps intentionally have a negative coefficient.

I noticed that squeezing the bottom of the case shifted the freq noticeably.  
Temperature could also distort the case, I theorized.  So, I placed a copper 
foil shield between the bottom and the VFO area.  This solved the mechanical 
problem.

I also came to the conclusion that the Elecraft design compensation is 
acceptable *IF* all the critical components change temperature at the same 
time.  I noticed that even a small amount of temp change (I do not mean 
static temp level) from a 20 minute QSO could cause 100 HZ of drift.  The QSO 
shift seemed more apparent with the box cover on than with it off.  So I 
inserted a couple layers of Saran Wrap between the bottom and the ckt board, 
and on top of the VFO.  The purpose is to slow temp change of the VFO, so 
that the components will more likely change temp at the same time.  I also 
inserted a third layer over the top to help keep desert dust from the board.  
(My box has some cracks between aluminum covers that will allow entry of 
dust.)

This all seemed to help.  At least, the drift was acceptable, even when the 
box was hot to touch.

Hope this is useful to someone.

... Reed K7FLY K1 #453
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Date: Mon, 12 Nov 2001 17:05:30 -0800
From: alta <alta at alta-research.com>
Subject: Re: [Elecraft] K1 drift: What's normal?

Lou ...

I had drift problems too.  Here's what I learned.

1. The sensitive components are chosen by Elecraft to cancel drift.  
Therefore, any substituted components (regardless of how good they 
are) can cause increased drift.

2. Good voltage regulation is EXTREMELY important.  That's why they 
use two voltage regulators.  My VFO voltage reg was temperature 
sensitive. I replaced it with a different one (but same part number), 
and stability was improved.

3. I put a copper-foil shield on the bottom of the ckt board near the 
VFO to reduce drift caused by mechanical changes in the box bottom.

4. I put several layers of Saran Wrap over the VFO components in the 
box so that they would heat more evenly.  (Because transmitting 
increases the temp in the box.)

At first, I thought everyone else's rigs were drifting.  I felt 
embarassed when I realized it was ME.  Now, with the above changes, 
the drift is acceptably low.

... Reed K7FLY

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