Stupid pitch-preview question

Posted: 2/2/2014 8:17:41 PM

Joined: 4/28/2005

One could think of a theremin as a poorly-shielded box with four radio frequency oscillators inside.  If one had an AM radio tuned to the frequency of the fixed pitch oscillator of a theremin (~ 290 kHz in the case of the Etherwave), and one played the instrument to a pitch of a concert A (440 Hz), if the AM radio was picking up the emissions of both pitch oscillators, both frequencies went into the detector, wouldn't the speaker of the AM radio also emit a pitch of concert A? 

I am wondering if this principle could be used to make a non-invasive pitch preview that could be used (hypothetically) with any theremin.

Or, was that the stupidest question ever?


Posted: 2/2/2014 10:28:54 PM

From: Colmar, France

Joined: 12/31/2007

Just try it out and you will see... ;-)

This will give you much more insight as when I tell you everything here. An AM receiver which works in the long wave range (150kHz to 350kHz) is cheap and easy to find around 10$ in an analogue version and around 20$ with digital PLL synthesized tuning. No risk, no fun! But you'll perhaps guess it: If this was a reliable method, we all would already be using it...

Posted: 2/3/2014 5:38:42 AM

From: Tucson, AZ USA

Joined: 2/26/2011

I just tried the radio trick and found a digital radio was worthless but an analog AM Radio tuned to triple the EWS theremin frequency (286 kHz) 858 kHz works good. Hopefully you do not have a radio station joining in your session plus I should mention it is not as clean as a direct connection. Other quiet heterodyning background birdies were apparent; it could work in a jam.


Posted: 2/3/2014 12:51:32 PM

From: Eastleigh, Hampshire, U.K. ................................... Fred Mundell. ................................... Electronics Engineer. (Primarily Analogue) .. CV Synths 1974-1980 .. Theremin developer 2007 to present .. soon to be Developing / Trading as . ...................................

Joined: 12/7/2007

"I just tried the radio trick and found a digital radio was worthless but an analog AM Radio tuned to triple the EWS theremin frequency (286 kHz) 858 kHz works good." - Touchless

Thats real interesting, T ..

I have never played with AM radios for theremins - (not at all surprised DAB radio never worked ;-) - I never bothered with AM radios because I feared results would be untrustworthy, unless a real simple radio was used (was worried about the effects of the radios LO and getting spurios audio as a result of heterodyning with this).

But I am surprised that 858kHz (f*3) worked - I wouldnt have expected there to be enough 3rd harmonics on the antenna waveform.. Kind of worrying from a RFI perspective - I wonder how high the harmonics go and what strength they are..

When I have played with EW oscillators I have always observed really clean sine waves on the antennas except when the oscillators are close to lock.

I suppose the EW is better suited to this kind of "preview" as its oscillators are simply coupled to the mixer - I wonder if it works so well when the signals are buffered (as with Thierrys ESP add on) or other theremins with buffered oscillators, and / or how much of the reference signal is coming from the antenna vs how much is being directly radiated from the board..

Real interesting though - I should knock a simple tuned circuit "radio" together and give it a try -   



Posted: 2/3/2014 8:15:25 PM

From: Scotland

Joined: 9/27/2012

I've had a play with my wee AM radio too and there is a detectable signal all the way up to (f*4) but the sweetest is f itself (approx 280Hz) since the signal is strong and there is very little else going on at that wavelength.

DAB radio...pah!


You must be logged in to post a reply. Please log in or register for a new account.