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Old 27th Jan 2018, 12:16 am   #16
MrBungle
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Join Date: Jun 2016
Location: London, UK.
Posts: 3,687
Default Re: Compensating for VFO drift

Ok spent the evening on this, between being stressed about a pizza delivery, and some results finally. I have basically read all the books and articles suggested and come up with a Hartley oscillator instead from a W1FB design.

Dug around in the junk boxes and found a whole bag of 1971 dated 2n4416's and some enameled wire and went to town on winding my own coil. It is wound on paper on an X-Acto knife (exactly .3 inches in diameter) with masking tape over the ends and a fetching colour of nail polish stolen from my eldest to finish. tapped 1/4 of the way up. Measured at 4.7uH, a little higher than the 4.4uH predicted.

Is it stable? Considerably better. After 5 minutes of settling it drifts about 20Hz/minute which is pretty good. It is currently residing in a cardboard box for lack of something better to stick it in. Because it works pretty well, I'm going to reduce all the coupling capacitors considerably from 22pF down to about 10pF and see if it'll still start. This should give better load isolation.

Work in progress (horrible looking I know):
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