Updated 06.29.08

Lev's Ultimate Antenna Construction

This antenna design is the whisper "True beauty hidden in Simplicity" 
This was revealed in the vision of November 2003   Christopher

Antenna Schematic
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Lev's Antenna can work with my RS Theremin, PAiA Theremax, Theremaniac, SWTP 142
or any heterodyne theremin operating in the range of 800khz to 1200khz.

Antenna Schematic

The antenna C4 capacitor & L3 ferrite rod coil are connected in series and built as a module on a generic circuit board as seen like Radio Shack Cat #276-50.

Also see Adjusting the C4 Antenna capacitor down below on this page.

Pitch re-adjustment
The antenna loading effect will move the frequency of your pitch considerable. You need to offset this by increasing the inductance of the reference oscillator coil L2. On the RS Theremin slide a 100 uh RF Choke  ferrite core into the L2 coil to counter the antenna loading effect. Adding ferrite or more turns to the L2 reference oscillator coil will increase the inductance. On some theremins adjust the L1 ferrite core to lower the inductance of your L1 coil.

RS Theremin builders you may want to revisit the "Tuning the Oscillator" webpage to re-tune with the Lev Antenna attached.

The 6 1/2" octave spread on my antenna tuner board occurs with the C4-T antenna variable capacitor adjusted just past the halfway point counter-clockwise. Use your pitch adjuster knob, set A2 at 16" away from the antenna using the Keyboard Graphic & Pitch Tuner.

If F2 or G2 shows up in the middle where A3 should be on the keyboard graphic using a pitch tuner, you need to increase the C4-T antenna capacitor slightly, this will center A3 between A2 and A4.

Counter-clockwise increased the capacitance using the antenna tuner variable capacitor. When using the keyboard graphic, if A2 & A3 line up correctly and A4 is a narrower octave, move the playing area or keyboard graphic stick 2" away from the antenna laterally.

You want your pitch hand to play into the center area of the vertical spring coil, so try and set your linearity with regards to this area, though it is not critical the linear field for play is very wide.

Lev's Antenna with minor stretch adjustments and the Antenna Tuner Circuit create the linearity. Your RS Theremin pitch "null" adjuster screw in L2 sets note A2 220 hz at the 16" (40.6 cm) distance from the spring coils vertical center. Use this 16" (40.6 cm) measurement when validating the linearity against the piano keyboard graphic.  

After linearity is set up moving the A2 note closer to the antenna with the pitch adjuster will reduce the octave width for tighter linear play. You might want to set the octave width to match the size of your hand for more effective aerial fingering.

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"The key is to tune the Antenna Tuner just below the pitch oscillator frequency."

Adjusting the C4 Antenna tuning capacitor might prove challenging so try this:

Hearing a Null point sweep by while tuning the antenna capacitor has nothing to do with tuning the antenna in the test below.

Place a (analog) AM Radio about 2 or 3 feet away from your antenna.
Tune the radio to where you hear your theremin whistle.

Try and throw the theremin whistle out of range (silenced) by placing the 100 uh ferrite choke rod into the fixed L2 pitch coil, you want to hear the quiet spot on the AM Radio created by the L1 pitch oscillator.

or

On the RS Theremin connect a alligator clip test lead & wire onto the Collector side of the NPN transistor, this is the Q2 lead toward the coil and let it dangle to disable the L2 reference oscillator from oscillation. 

When the theremin whistle is quiet you should hear the natural background static in the AM Radio and your theremin L1 oscillator hissing very quietly where it is transmitting to this tuned spot. Adjust the Lev Antenna C4-T antenna variable capacitor back and forth (not the radio) to find the spot the static heard in the radio becomes the quietest, make a mental note or mark this for all future re-adjustments. This is the point the antenna is tuned to the L1 pitch oscillator frequency. I don't think it would need re-adjustment once your theremin is complete and operating properly, protect your setting from unwanted access.

Finally, remove the 100 uh ferrite choke or alligator clip wire to re-ignite the L2 reference oscillator. You will need to retune the C4-T antenna variable capacitor "slightly" to either side of the noted quiet tuning spot to adjust how the linearity is lining up when you have the piano keyboard graphic setup for reference.

or  - Just experiment until everything becomes obvious!

Note:  The ideal response from the antenna is when the antenna is tuned to just below the L1 pitch oscillator frequency. Stretch the antenna spring coil about 1" (25 mm) to maximum equalized octaves, for linear behavior. (The least amount of spring stretch works best for me, check the spring stretch by feel. A piece of typing paper should slide in between the coil gaps snuggly.) 

Note: Background noise picked up by the theremin antenna is reduced or eliminated by keeping the feed wire from the circuit board to the Antenna Tuner as short as possible. Around 6" (15 cm) is ideal. 

The distance from the tuner to the Lev Antenna spring must be slightly more than 6".

Note:  You do not need a pitch tuner, use an octave jump to tune your theremin by ear. When you have linearity and the L2 pitch adjustment is correct for your personal octave width, a closed hand to open hand can make a the same note jump anywhere in the pitch playing field. This works well for the Carolina Eyck method of nine-position aerial fingering.

This initial frequency shift after a new installation of the Lev Antenna is from the loading effect cause by the increased transfer of energy into the theremin pitch playing field.

You want your antenna tuned to just below the theremin pitch oscillators RF frequency, this is not critical, just don't tune higher than the L1 pitch oscillator frequency or you will get a flipping effect in the theremin pitch audio sound. This is caused when the pitch "antenna tuning" is higher and it crosses to below the theremins pitch oscillator frequency.

A properly designed theremin has a response out to several feet but our main interest is in the response of the standard playing field which is reaching from the chest to the antenna. This is normally no more than a 20" range but usually played much smaller as you observe most Thereminist.

Using Lev's Antenna I found the Theremaniac Theremin would adjust to just over 3 linear octaves while my latest RS Theremin design measures in at just over 5 linear octaves. The number of octaves comes from the amount of energy driving the Lev Antenna from the pitch oscillator LC coil setup and it is the Lev Antenna design that gives you the linear octave pitch field.

Most theremins using a standard antenna can whistle across a much wider range of octaves if you accept them cramming most of their energy around the antenna. This is what makes them non-linear.

"Setup Lev's Antenna correctly and you find yourself in a new reality of theremin control.
Immediately you will notice something wonderful is happening."  Christopher