<html><head><meta http-equiv="content-type" content="text/html; charset=us-ascii"></head><body style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;"><div><br><blockquote type="cite"><div>On 1 Dec 2025, at 09:59, rburnett@richieburnett.co.uk wrote:</div><br class="Apple-interchange-newline"><div><div>It will work. Varactor (varicap) diode VCOs are nothing new, although they usually use a diode designed specifically for the job instead of an LED! Likewise the hetrodyning (RF product "mixing") is a well established technique in radio transmitters/receivers for shifting frequencies up or down.<br><br>The downsides of varicap VCOs are drift and poor linearity (MHz/volt) of the control law. Both of these issues are typically solved in a modern radio transmitter or receiver by making the VCO be part of a PLL structure. This locks the VCO frequency to any one of a number of multiples of an accurate (crystal) reference frequency. Then you get the best of both worlds: adjustable frequency with perfect control linearity, combined with crystal accuracy and low drift.<br><br>If you mix together two RF signals up in the MHz to produce an audio tone the resulting pitch will be *incredibly* sensitive to tiny percentage changes in either of the RF oscillator's frequencies, and things like phase noise. Whether the result sounds to your liking is another matter! I'd expect it to sound like a Theremin because that's essentially the mechanism that it uses to generate audio.<br></div></div></blockquote><div><br></div><div>Minor detail, in the Theremin, the hand-waving *is* the actual change in capacitance. The antenna is part of the tuned LC circuit in one of the oscillators. So no varicap diodes needed. Here is an early article from master theremin builder Bob Moog: <a href="https://ia600107.us.archive.org/23/items/synthmanual-moog-the-theremin-article/moogthethereminarticle_text.pdf">https://ia600107.us.archive.org/23/items/synthmanual-moog-the-theremin-article/moogthethereminarticle_text.pdf</a></div><div><br></div><div>Ben</div><div><br></div></div></body></html>