Antenna range on practical electronics project.

Hello. Been working with the handheld theremin from everyday with practical electronics project in the schematics archive here on Thereminworld. Its a fun little project but after spending some time constructing it I found that it only has about 4 or 5 inches of range. being that I can play at least three octaves within a 2 or 3 three foot range of my etherwave I wanted to be able to play my handheld hanbuilt project this way as well. What can I do to increase the range on it? I read an article by Moog and he uses a tuned antenae to change the sensitivty of the Theremin constructions but I want to change the range not sensitivity. I figured that this either had to do with the operating frequency of the oscillators or the wattage. Also the project isn't temperature stable. what can I do to alter the stabillity of the oscillators? I've read some articles that describe a certain feedback network in amplifiers for temperature stabillity of transistors shifting beta, but how would I employ this in oscillator tanks?

Range and sensitivity are related.. Putting an inductor of the RIGHT value between the circuit and the antenna will increase the range.

calculated the frequency of the pitch oscillator at around 28 Mhtz. What would be the right value coil to put between the antenna and the circuit?

[i]"calculated the frequency of the pitch oscillator at around 28 Mhtz. What would be the right value coil to put between the antenna and the circuit?" - Puff[/i]

Ok - your calculated frequency must be way out!! Pitch oscillator needs to be somewhere between 100kHz and 1MHz.. Usually between 200kHz and 500kHz. But this particular Theremin has higher than usual frequency of 1.33MHz (acording to article)

My expierience is that higher frequencies tend to produce Theremins with reduced range, and are much more difficult to 'get right' .. inter-winding capacitances in equalizing inductors become far more significant, while inductance required is smaller than for lower frequency designs - this makes the 'balance' between the tank (oscillator) LC components and the antenna LC components far more critical.

Quick calculation using 1.33MHz and 12pF antenna capacitance gives an inductance value of 1.2mH .. But this does not take any leakage capacitance into account.. At this high frequency the coil value and construction will be critical.

To be honest, if you want a Theremin with reasonable range, stability, and linearity, I would advise you to drop the frequency to below 500kHz.. This can easily be done by increasing the capacitances in parrallel with the inductor of the tank circuit.. This will decrease the frequency AND decrease the sensitivity of the present circuit (the antenna connection will be much less sensitive) - But, adding a equalizing inductance will then GREATLY increase the sensitivity. See ThereminLCF2.XLS which provides the needed worksheets to calculate both the tank (oscillator) and antenna component values.



see Calculators for antenna.. (http://www.element-14.com/community/docs/DOC-16905/l/calculators-for-antenna-capacitance-and-other-functionsxls)

and ThereminLCF2.XLS (http://www.element-14.com/community/docs/DOC-16874/l/thereminlcf2xls)

Final advice.. Unless you fully understand everything I have just said, it is most unlikely that you will turn this simple Theremin circuit into a 'good' Theremin.. This design really isnt worth spending much time on, it is really just a toy. If you want to make a musical instrument, start with a better 'core' design - something like the EPE 2008 or the Moog EW, or even one of the Art Harrison simple designs - You might even get better range and playability from a simple 'digital' circuit running at 300kHz.