EMRFD Message Archive 451

Message Date From Subject
451 2007-02-08 08:39:38 Stan Series tuned Clapp VFO questions
I am looking at Solid State Design Page 34 Figure 2B.

I do not see the Tuned Clapp circuit used very much in qrp VFO circuits.
However, when reading the text it looks like a reasonable ckt to use.

I plan on using a FET. The feed back caps would be of high value at 5
MHz so my thinking is that they would swamp out small changes due to
heating, loading, etc in the FET circuit. The series L is higher
than normal in a similiar VFO circuit so the external influences should
be less. Am I on the right track here?

The tuning cap value to cover a 0.5 mhz is low but the overall C series
value is high.

I would be interested in others comments on using a series tuned Clapp
with a FET on 5 MHz? I am assuming the FET is better to use than a

Thanks, Stan ak0b
455 2007-02-10 22:57:36 jr_dakota Re: Series tuned Clapp VFO questions
I think the biggest drawback is the size of the inductor compared to a
parallel tuned circuit of the same frequency which becomes really
relevant in low frequency LO's and the need to keep size small in QRP