I'm building a FM receiver based on a SA615. But when I test the VFO (variable frequency oscillator) with a spectrum analyzer and a sniffer probe I don't see any frequency showing up. So the oscillator isn't starting up.

The VFO circuit I made is composed of salvaged radio parts. Like a fm radio tuning capacitor, and the coil of the radio's loc osc. The circuit I use is this one:enter image description here
Where VAR-CAP is connected to the FM tuning capacitor.
And OSC_OUT to pin 3 of the sa615 (emmiter) and OSC_IN to pin 4 (base).
My circuit is based on following examples: enter image description here and this enter image description here

I hope someone can give me some tips or see whats wrong with it.

Thanks in advance!

  • 3
    \$\begingroup\$ Comparing NE602 second circuit and "Fundamental Crystal" they both connect base (pin 6) to the top of the tank, and emitter (pin 7) to the tap, while you claim to do the reverse. That may be relevant. (NE602 data sheet) pdf1.alldatasheet.com/datasheet-pdf/view/107776/PHILIPS/… \$\endgroup\$
    – user16324
    Nov 23, 2015 at 18:46
  • \$\begingroup\$ thnx for the fast response I'll try it the other way around. \$\endgroup\$
    – Bruce
    Nov 23, 2015 at 18:50

1 Answer 1


enter image description here

You have in and out the wrong way round. It's meant to be a colpitts oscillator.


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