Antennas & antenna coils for EM theremin

"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.

Fred.

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.

antman,

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.

Christopher

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

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

I place it 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).

Thanks a bunch