EMRFD Message Archive 2465
Message Date From Subject 2465 2008-12-01 11:42:07 timshoppa Linear-tuning VFO's The HR article with the eccentric pulleys was interesting.
I also found very interesting the way that folks here, in the past,
have linearized potentiometer-tuned varactor VCO's with nonlinear
tuning voltage networks and 10-turn pots. I think there are some
schematics in the "files" section of this board.
Another way of doing this is properly spacing the windings on a PTO. I
have a lot of respect for, say, the Collins and descenendant PTO's in
390A's with their mechanical corrector stacks. But homebrew-mechanics
wise, the QST article I've always wanted to replicate is I1MK's
article in July 1964's QST. He shows a 500-kHz wide 25-turn PTO
mechanism, with 20kHz/turn tuning rate, and tells how to correct it to
500Hz worst-case. (He says this is 0.02% but I disagree, it's only
0.1%, he "cooked the books" with some clever math but 500 Hz is still
pretty good for not having a corrector stack).
I suppose all this dial-linearization is simply passe in the days of
few-dollars, low cost low weight frequency counters. But I still think
2466 2008-12-01 15:52:04 jr_dakota Re: Linear-tuning VFO's Most people don't realize it but a good source of PTO's for
experimenting is from old 60's and 70's era car 'pushbutton memory' AM
radios, many of which are fairly linear in their tuning ... The reason
they were used in car radios in the pre-digital age was their tuning
linearity and stability to vibrati