Thread: Franklin VFO ?
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Old 16th May 2019, 12:45 pm   #36
G0HZU_JMR
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Join Date: Sep 2010
Location: Cheltenham, Gloucestershire, UK.
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Default Re: Franklin VFO ?

Quote:
I've just come across a bit in G3VA's Technical Topics from June 78 Radcom. This is a Franklin designed by ZL2APC, which seems to have a rather more sensible biassing arrangement than some of the others I've looked at. He uses two 2N4360 P-channel devices, but it would work fine with supply polarity reversals and N-channel devices where appropriate. Well worth consideration, I think.
Yes, the VE3RF circuit is very simple and seems to work well but I think it could be a bit unpredictable in terms of loop gain (it might not start with some JFETs) and the resonator voltage may vary a lot because of the way it can be so affected by the JFET characteristics. On a simulator the changes I see across 2N5484 through 2N5486 are quite dramatic.

However, I have to say that this lashup version of the VE3RF oscillator I have in the screened box is probably the most stable 5MHz oscillator I've ever made and I've changed nothing on it since the initial build. I did include the subtle phase correction in the initial build. Up at 16MHz I think the gain/phase error will be less because there will be some phase shift in the overall circuit anyway at the higher frequency.
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Regards, Jeremy G0HZU

Last edited by G0HZU_JMR; 16th May 2019 at 12:54 pm.
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