Antenna tuning.

I added the 20mH extra to the antenna and it sounds much better. You said that you want the antenna and coils to form a resonance just below that of the tank circuit. Since I can easily tune the tank using the variable capacitor is there an easy way I can know whether or not it is tuned well in reference to the antenna circuit? 

"Since I can easily tune the tank using the variable capacitor is there an easy way I can know whether or not it is tuned well in reference to the antenna circuit?"

Note: If you experience excessive thermal drift the variable capacitor is not your friend.

This is simple, nothing new here. . .

The tank LC must be tuned slightly above the antenna circuit. You want to avoid frequency crossover as your hand approaches the antenna. Crossover can create an obvious no response dull spot in the pitch field as your hand approaches the antenna. It is a fascinating event that only a handful have experienced, I only know two people!

I will say no more, don't want to give it away, school is in session.

We have two excellent active engineers on this board these days except one is backwards.

I guess I'm just wondering how to know if the antenna is tuned slightly below the tank. I don't know the exact antenna capacitance so I can only guess what it's actually tuned to.

This "no response dull spot" mentioned above is actually moved by tuning the pitch oscillator and moves away from the antenna to behind you. This event is a completely different than tuning a normal theremin Null or Zero point. Both of our engineers are close to understanding what I am talking about, they are being led, but not there yet! In one sense these events are similar as the zero/null is between the two oscillators and the dull spot is between the pitch oscillator and antenna. Something special is revealed to those that find the dull spot or The D-Spot.

This is simple, nothing new here. . . <= I only say this so he doesn't! (-'

There is a practical method for you to tune, but an engineer must give you this answer.

Here is the practical method. I just scribbled it on my iPad. You may download it as a PDF file. :-)

Our friend Christopher aka rs theremin tries to give us some keywords but he seems to be not willing to talk about common phenomenons like poles and asymptotes in complex resonance curves. As long as he does not give his explanations, I don't see how I could rationalize them afterwards... ;-)

Ok, I'll try that next time I get a chance. Thanks, Thierry. If you don't mind I would be very curious to hear a more technical explanation of how the antenna resonant circuit affects the tanks resonance.

"...I would be very curious to hear a more technical explanation of how the antenna resonant circuit affects the tanks resonance."

Download my spreadsheet and play around with the values.  I've learned the hard way that the simulator in my head is no match for four interacting energy storing passives.  Kind of sad actually.  I even took a filters course in grad school (and have the book gathering dust to prove it).

Several here know seriously more than I do, but my takeaway is that the real resonance is with the larger "linearizing" coil and your hand.  IMO the tank resonance is more a way to excite this dominant LC (and keep the transistor happy) than anything else.

I tried the method you prescribed, Thierry. Unfortunately the minimum voltage displayed by the multimeter (.483 V) was when C1 was at it's minimum. Does this suggest that I should add some capacitance to the tank circuit?

Oops. I meant to say that maybe I should remove some capacitance from the tank.

I always try and write with humor and sometimes it just does not work, I will try harder. If I pick at engineers, it is only because they understand things I don't and never will because time has dampened my youthful mind.

When I started my research all I was attempting to do was recreate the AM radio transmitter I had made in the summer of 1963. I had my first crush that summer, talk about mystical. How I got directed toward theremins I am not really clear but here we are today and I have learned some things truly special.

Christopher