Need some help with pitch antenna inductors.

Wow, guys, you are amazing. Never before I've got such detailed help on any forum. Thanks! 
About the strange apparatus theremin: I've found it by just googling "simple theremin".
Now, I haven't yet understood everything that Thierry wrote, but I sure will figure it out. I guess I have to just sit down and do some reading, starting with the link you've provided. 
But still, what can you say about those toroidal inductors made out of thick wire? Will they work at all? 

Toroidal inductors may not be enough stable, their inductance depends among others from temperature. That's why ham radio amateurs use them mainly for non-frequency-critical purposes, i.e. wide band RF transformers, but rarely in tuned tank circuits.

I think that this is one of the reasons why they never appeared in theremin designs up to now. 

Another kind of inductors which is also easy to manufacture are those with air-gap pot cores. The British engineer Anthony Henk who built instruments in the early nineties for famous thereminists like Lydia Kavina, Celia Sheen, Bruce Woolley and for the BBC used them in his designs. I had the occasion to study and to fix last year his very first prototype which he built for and with Lydia. I found his variable oscillator built around these pot core inductors circuits rock stable, so that he had no problem using a 153.6kHz xtal in the fixed pitch oscillator.

Wintermute said: “Wow, guys, you are amazing. Never before I've got such detailed help on any forum.”

In the world of theremin it is common to build you up before we tare you down, it is therapeutic for us. I have no doubt you will experience heterodyning with the Strange but I also guarantee the thermal drift you will experience will be horrendous.

If I may ask, are you male or female? Are you in the States? Have you ever soldered before?

When is your birthday?  Just kidding, but what year were you born? How can anyone help you if they do not know where you are coming from or where you want to go with the theremin?

Theremin building requires you build upon the successes that came before you, not the failures and there are many. If a design or designer does not share a sound sample of their work, it is doomed.

Christopher

I'm male, 27. I'm studying Mechatronics (robotics) at Simon Fraser University in Vancouver, Canada. 
Yes, I can solder. I'm making the theremin just for fun. I always liked the idea and I think the  working principle is quite interesting. I play a violin, so I hope I can learn to play a theremin a little too. 

About the resonant frequency of antenna and 4x10mH inductors in series: Is it a good idea to rely on the value of 251 kHz or is there a way to measure it more precisely with my particular antenna?  (I have access to oscilloscope and a function generator).

Win - we are in the same time zone which works out perfect when burning the midnight oil <= what ever that means. My approach to theremin building is different than most so the others here are needed to help you with antenna tuning methods using pot core coils and what not.

Edit: A frequency counter is the first tool for theremins, an oscilloscope is good for looking at basic audio wave shapes but will not reveal what creates an authentic theremin sound, your ear works best. A theremin voice is alive and changing, not a dead sine, triangle or nasty square wave.

Enjoy the Journey

Christopher

Thanks!

I mainly use oscilloscope as a frequency counter. It's a digital one and it measures frequency. I hope it's accurate. 

What if I buy a spool of 200ft of magnetic wire and use it as a ready air-core inductor? I guess I would just have to remove little wire from it to get 10mH. Is it a bad idea? Should the turns of wire be spread out over a larger length? 

"What if I buy a spool of 200ft of magnetic wire and use it as a ready air-core inductor? I guess I would just have to remove little wire from it to get 10mH. Is it a bad idea? Should the turns of wire be spread out over a larger length?"  - Wintermute

Won't work, self capacitance will make it resonate with its inductance at too low a frequency.  But if you put a single layer of it on a large enough plastic or phenolic pipe you'll get an amazingly high Q, low self capacitance air-core.  Pick the smallest diameter wire you feel comfortable working with, I can't go below 34 AWG without disaster ensuing.  I have a spreadsheet to calculate these if you are interested.

So, what exactly causes that self-capacitance? Large number of layers of wire?
If I put the wire on a plastic tube, does the thickness of the tube matter? 

"So, what exactly causes that self-capacitance? Large number of layers of wire?  - Wintermute

I believe it's mostly one end of the winding "seeing" the other end capacitively.  You can place adjacent windings together, but you want to separate them from non-adjacent windings.  Does that make sense?  If you look at the construction of low capacitance coils you'll see multiple scramble-wound "donuts" separated from each other, or you'll see one long continuous single layer winding.  You'll also likely see ferrite, which can dramatically reduce the number of windings necessary but introduces temperature dependence.  If you see ferrite you'll probably also see an insulator between the windings and the ferrite, to reduce capacitive effects.

"If I put the wire on a plastic tube, does the thickness of the tube matter?"

The tube diameter very much matters, but the wall thickness of the tube isn't a huge deal electrically.  Mechanically you might desire a thicker wall for temperature stability.  The permittivity of the tube material doesn't seem too important either, as long as it is low.  Relative permittivity of schedule 40 PVC is around 3.

Here is my spreadsheet: http://www.mediafire.com/download/8n88bg2kojdj5ve/Theremin_simulation_v9_2013-08-30.xls

You want the "Inductor Design" tab.

Thanks! Looks like a useful tool. You must have spent a lot of time assembling all those calculators!