Theophony: The Mighty Interactive Theremin

Hello All,

Burning Man - Nevada

The group from Salem, MA met their $8000 funding goal this morning, right on deadline. hum…

Steve Martin (not that one)  has worked for the last 25 years with companies like Boston Acoustics as an electronic engineer developing the stuff that brings us all quality sound. He is our designer for the optical proximity oscillator thus we call it a "faux theremin".

The problem I have with this project is. . . only a true theremin can create the effect they are looking for. Maybe I can give Steve an idea or more. They still have a month to go and I have gathered information from our own engineers at TW on how to get the maximum pitch field diameter. 

I will be setting up in my backyard this week and observe something I have questioned for a while. A few people know a theremin transmits a radio signal (energy) through a dual electrical/magnetic equilibrium (sounds like something you wear on your wrist) that can be picked up by a AM Radio tuned to that frequency. I would like to see if there is any correlation to the edge of the pitch field and how far the AM signal is still detectable. Stop rolling your eyes!

Whether or not I get involved in the BM project, above is my plan for the week. I will post a photo of the crude setup.

Christopher

"I would like to see if there is any correlation to the edge of the pitch field and how far the AM signal is still detectable."

I'm interested to learn what you discover.

Coalport... "they" are all dead now sir, we are getting older. )-:

gtc, thank you

dewster said: "I agree with FredM, the limit is set by the electronics, more specifically stability and thermal noise.  If you could stabilize it sufficiently, and if you could tolerate a (possibly huge) lag in the response, you could average the noise down to the point where you could probably detect someone picking their nose across the street."

dewster I apologize, I picked on your wave length calculation for a reason I am not sure why. I can see the logic in thinking of the theremin pitch antenna as a quarter wave dipole with the loading point way off center, wonder what the impedance match might be? The earth could make up for the wave length short comings?

To just say the pitch field "Outer Limits" are set by electronics is really not telling me much to help my experiment this week.

I went to the store and the experiment will proceed, it is more something to do and find out what is possible. When people in the past have said they want to build a really big pitch antenna, "they" might think size is what counts for pitch field expansion. (It could be?)

My goal is for a usable 8 feet in distance, this would be a 16' diameter. What do I consider usable? Maybe 10 pulses per second to start PWM to control a rising sound level, in other word 8' (2.4 m) of volume shading. My boards do have pitch oscillators and volume control on them so a true theremin is "almost" the appropriate term.

I will be using 20 to 30 feet of a single stereo cable for remote-tuning, tuning-indicator LED and Muting. A human will monitor the control though it is very stable in the short term.

Now I wonder how Fred kept all his theremins tuned over the course of the day.

Christopher

As far as impedance matching goes, it would be a small fraction of an ohm.

As a ham radio operator, I've transmited around 3.5 mhz with an 8 foot antenna.

A full size, quarter wave antenna for that frequency would be over 60 feet tall. Resistive losses on such a short radiator consumed a very large chunk of power due to low radiation resistance vs conductor resistance.

In the world of radio, the closer one gets to full size, the better it works. I suspect a theremin antenna might behave the same. Radio antennas are just tuned circuits where the wire / pipe / etc provides inductance and capacitance. The larger the conductors diameter, the shorter it can be for a given frequency.

A full sized, quarter wavelength antenna for 270 khz would be about 866 feet tall.

A good ground system is in effect the other quarter wave to make a half wave length dipole.

The half wavelength formula for wire antennas is.....Length (feet) = 468/f(mhz)

I'm giving this some thought...Stay tuned.

w0ttm here is what I am working with. I do not believe wavelength plays a part but maybe it could? I use a coiled pitch antenna that has marvelous characteristics.

Pitch Frequency = 925 kHz

Full Wave Length = 1064 feet

Quarter Wave Length = 266 feet

Spring Coil Antenna = 9/16" x 16-1/2" x .054" (14.3 mm x 419.1 mm x 1.372 mm)

The actual length of the compressed coil area is 15.75" at 16 turns per inch (approx. 252 turns at a ½" diameter)

(1/2” x 3.14 x 252) / 12 = 33 feet

Christopher     WD6EDZ

"dewster I apologize, I picked on your wave length calculation for a reason I am not sure why." -RS Theremin

Thank you, and I apologize as well.  We're all in this together, regardless of how we approach it.

@ Christopher: I'm looking at that style as well, and thrilled to find another ham!

Antennas for theremin vs HF appear to follow different rules.

I've read about your antenna, and can't figure out how it works. with those dimensions, it would work as a loaded quarter wave on 10 meters, or there about. The ones I've built for HF had about a half wave of wire on them.

I'm so tempted to throw a hamstick at my old Kustom and see what happens. It runs at about 250khz, so maybe a 40 meter helical would wake it up.