A quick follow-up to How can I tell the frequency without an oscilloscope, or frequency counter?

My supply is a transformer plucked from a dead power adapter rated for 1.5A. This is rectified cap-filtered, then Vo manipulated through an LM317 with a pair of 1k linear.

I plan to tap the capacitor output to power the oscillator, and use the 317 output to bias the varactor.

Does the varactor bias supply have to be distinct from Vcc?

  • $\begingroup$ What do you mean by "independent" or "distinct"? $\endgroup$ Nov 26, 2014 at 12:23
  • $\begingroup$ Just that. E.g. Vvaractor = dedicated battery $\endgroup$
    – VU2NHW
    Nov 26, 2014 at 12:27
  • 1
    $\begingroup$ Then the answer is no. The question might be better if you explain why you think a separate battery is necessary, then there would be more to say than "no". $\endgroup$ Nov 26, 2014 at 12:29
  • $\begingroup$ Let me catch you in the shack ... hang on. $\endgroup$
    – VU2NHW
    Nov 26, 2014 at 12:30
  • $\begingroup$ @VU2NHW So if the discussion has been had, is there an answer to this question now? $\endgroup$
    – Kevin Reid AG6YO
    Nov 27, 2014 at 19:43

1 Answer 1


No, you can derive the bias from Vcc just fine. You will want to make sure the bias voltage is well-regulated and low-noise, since any error or noise will be manifest in the tuning of your radio. Nothing that can't be accomplished by a voltage regulator and a bit of filtering, however.


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