[Boatanchors] VFOs drifting

[Steve Uhrig]

I've read with interest the posts on the Boatanchor list about the 
gentleman wanting to build a solid state VFO for his old Heathkit, and 
other's comments on VFOs drifting and solutions.

Let me relate a little story.

When I first got my general, around 1972 as I recall, I was a poor farm 
boy shoveling manure and doing related chores to buy radio parts.

My Elmer, who only had a Tech license and couldn't operate HF (back then; 
I have no idea what privileges a Tech has now) built a Heath Cheyenne 
transmitter for the learning experience. That was a CW/AM mobile 
transmitter which used an external supply. Internal VFO, and screen 
modulation for AM instead of plate modulation.

Well, I tapped off my Hunter CM20 (?) CW transmitter for power for the 
Cheyenne, coupled it with my 2B, and put it on the air.

The bloody VFO drifted incredibly bad. Would walk up the band, smoothly 
and steadily. In the space of maybe 20 minutes, I'd be at the top end of 
40 meters.

I went to my Elmer for help. He admitted the thing drifted, several 
others had worked on it unsuccessfully, gave up, and that's why it was 
gifted to me.

My dad, a thoroughly competent electronics engineer who had been a ham 
when he was a kid, looked at it. I seem to recall some comments he made 
that he wasn't going to re-engineer the thing from both an electrical and 
a mechanical standpoint.

I played with every trick I could learn, followed stuff from the 
handbook, asked on the air. No luck.

My dad, who is an old German craftsman with all things mechanical as well 
as electrical, fixed the problem for me, but in a nontraditional manner.

He coupled a little square motor from a battery operated toy race car 
through a pulley and dial cord arrangement to the VFO knob, through a 
rheostat. By playing around some with the rheostat, I could make the 
motor turn the VFO down knob at about the same speed the VFO drifted up --
 at least enough to keep me in band and let the other side track me 
easier.  

I used that thing for some months in that fashion.

If one method doesn't work, consider another, and think outside the box!

Steve WA3SWS


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Steve Uhrig, SWS Security, Maryland (USA)
Mfrs of electronic surveillance equip
mailto:Steve at swssec.com  website http://www.swssec.com
tel +1+410-879-4035, fax +1+410-836-1190
"In God we trust, all others we monitor"
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