Antennas & antenna coils for EM theremin

Posted: 7/12/2012 12:03:06 AM

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

"Also, does anyone know if there's anything to gain using a frequency higher than 260 kHz?" - antman

All frequencies probably have some "gains" and some "losses" -

Higher frequencies require smaller linearizing (antenna) inductors, which tends to lower the cost a bit.. Lower frequencies (I think) are less likely to interfere with, or be interfered with by, other radio or EM emmitting appliances.

With lower frequencies, it is easier to retain the higher harmonics of the oscillator waveforms - but IMO this is not a big issue really as most often harmonics are produced mainly by mixer imperfections and deliberate 'distortion' of the audio waveform.. one does tend to find though that higher frequency theremins often produce a more sine-like audio.

It is easier to deal with lower frequencies as PCB / wiring capacitances and inductances are less critical (one gets less unwanted coupling).. I tend to think of 500kHz as the top frequency I would normally use for pitch oscillators, and 1Mhz as the top for volume oscillators.

Frequencies lower than about 200kHz add slight "difficulty" in rejecting the sum components - not a real difficulty, but one may need more elaborate filtering than just RC, as to get rid of anything lower than 400kHz sum adequately (as in, with no HF squeezing its way out on the audio with potential for trouble if taken to a digital effect or whatever) the RC might need to be big enough to slug the (wanted) audio high harmonics... Not a great problem at all (one usually has an opamp or other active component where you can implement a higher order filter easily) but probably woth mentioning.

To be honest, I have not actually played with many designs operating below 250kHz,  270kHz to 470kHz have been the main frequency range I have used.


Posted: 7/18/2012 9:48:25 PM

Joined: 7/5/2012

Parameter k is defined by the ratio h/L(corrected!) where L is a length af antenna and h is a distance between  antenna and conductive surface in the ideal model.

Some values of k:

h/L        k=

0.02 - 0.928 

0.04 - 0.884 

0.08 - 0.82 

0.2 - 0.702

0.4 - 0.604

0.8 -  0.504

2 - 0.408

5 - 0.352 

10 - 0.332 

 inf. - 0.307

ilya, i was running through these values and it wasn't really making sense to me. Sorry for asking, but how did you get the values of k.

Posted: 7/19/2012 12:29:46 AM
RS Theremin

From: 60 mi. N of San Diego CA

Joined: 2/15/2005


Remember the theremin only invites a few, the rest she plays endless mind games!  You can tell them apart by how often they scrap their approach as senseless and talk talk talk with no sound byte validation. Everybody is an expert.

You should not build any theremin design that does not furnish a sound byte you like.


Posted: 7/19/2012 5:42:16 PM

From: Theremin Motherland

Joined: 11/13/2005

antman>> Sorry for asking, but how did you get the values of k.

From the book:
 Iossel, Yury Yakovlevich at all. "Calculation of the electrical cаpacity" (2-nd edition),  pages 199-200.

It is placed here.
I think the tabulated D=0 for inf. is a typo. With a formula for D it must be  0.307.

The book in djvu format (in Russian).

Edit-2016: As the links above are died, I have placed the page 199 in TW photo album.



Posted: 7/20/2012 4:54:58 PM

Joined: 7/5/2012

Thanks a bunch

Posted: 10/16/2016 3:36:28 PM
Wesley Crispus

From: Chennai, Tamil Nādu

Joined: 10/16/2016

Hello Sir, I need the details about design a inductor eg: I need to design a inductor (were1996 Build the EM Theremin) of 40mH, 5mH & 2.5mH, for that I have a ferrite with 10mm length and 6mm dia,

-What gauge of copper I should select?

-How many turns I should wound to get the required inductor value?

-What about the frequency of that inductor?

Posted: 10/16/2016 6:49:01 PM

From: Colmar, France

Joined: 12/31/2007

When it comes to inductors L1 to L4 and L7 to L10, do not waste your time by trying out alternative solutions! Only these special 3-Pi wound 630x series Miller inductors or the compatible Hammond 1535 series inductors will exactly have the needed not too low not too high distributed parasitic capacitance which is needed to give a coherent tone spacing in the pitch field and a decent volume response. Both, the Miller and the Hammond ones can be ordered without problems online at the known distributors (Mouser, Digikey, and so on).
Posted: 10/17/2016 5:19:49 PM

From: Theremin Motherland

Joined: 11/13/2005

Wesley Crispus,

all you need are the sectioned former (at least  30 mm length, as many section as possible), wire 0.08-0.15 mm diameter and RLC meter. 

With the air core you need 3000-4000 turns for EQ coil and 1500-2000 turns for volume coil (the tap from 1/5). A ferrite rod allows to reduce the number of turns by 1.5-2 times. Never do layered winding by all the length, only section by section.

Posted: 3/18/2017 4:48:44 PM

From: portugal

Joined: 2/22/2016

"Use copper or brass tube for the antenna.   - will perform better and telescopic antenna just looks lame  -will make your all your hard work look like  Rabbit-ears/ TV antenna.  You could always just hand-wind large antenna coils.   1200 turns of #32 enameled magnet wire on a 3"( x12.5" cardboard tube ) will make the pitch coil~= 32mH.  Volume - 600 turns of #32 on 3" x 10" tube= 12.5-ish mH You'll just need to find a small 2.5mH inductor for the other part of the volume antenna circuitry. I built my first EM this way. Actually performed quite well. The lower inductance of the pitch coil compensates for it's larger capacitance.   (BTW- these are pretty much the same coils for the KEP tube theremin.) When I first built the EM i couldnt find any of the inductors, so I had to get resourceful.    I had good results with winding the variable inductors on surplus slug-tuned coil forms.  Id recommend having a inductance meter for that tho'."


Good afternoon.

Are you selling the 1929 RCA THEREMIN Pitch and volume coils?

I am trying to buy them?

How much will it costs?


Pedro Carvalho 

from Portugal

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