The Missouri* Waltz
When I first started out investigating Theremins, there being a dearth of technical books on them, I of course turned to the web. One web site that I found deeply intriguing was Christopher's (AKA oldtemecula, RS Theremin, Touchless, ...) because he claimed he had discovered the secret of a "perfectly linear" pitch field by connecting a simple one transistor LC oscillator to a common helical screen door spring "antenna". Stretching the spring slightly with a trivial screw mechanism reportedly made the oscillator response somehow "pop" or dramatically change at one point, and "perfect linearity" all the way from right at the antenna to quite far away was the result. This was the claim anyway, and one that Christopher has repeated countless times here at TW.
Naturally I went right out and bought the specified spring to experiment with it, hoping for the best. I unfortunately didn't have any success with it, but I chalked that up to my inexperience, my setup missing the specified oscillator, not holding my jaw right, etc. Since then I've come to understand inductors somewhat better (a passive component not covered comprehensively in my undergrad EE) and can say now that I see no obvious, physics-based electrical reason for how a slightly elongated spring might influence a Theremin in the manner claimed. The elongation separates the turns and insulates them with air, so the spring is then an inductor, but both the calculated and measured value of this, combined with the intrinsic capacitance of free-space, give a calculated resonance too far above the nominal oscillation frequency to be an obvious active mechanism to linearity. Perhaps something exotic like skin-effect or evanescent emission is going on? I doubt it, but if one really cares about scientific investigation (and I do!), things not properly investigated shouldn't be prematurely written off as impossible. Ah, but there's the rub.
Rule: The onus for investigating and proving, or at least convincingly demonstrating, any technical claims falls squarely and necessarily on the person making those claims. And fantastic claims such as this require rather more in the way of proof. The one making the claims is usually the most self-interested, and in the best position to do the investigating, so it's a win-win for all concerned. A sticking point in all this is the inventor in this case apparently loathes electrical engineering and those who practice it, so using technical means to prove technical claims is presumably out, leaving us with what exactly? Belief?
So I realize now that:
1. The phenomena (if it exists) isn't obviously explainable via simple physics.
2. Christopher will never explain the basis of this linearity phenomena (if it exists) in terms of physics.
I haven't visited Christopher's web pages in a while, but long ago IIRC there were pictures showing linear keyboards painted on measuring sticks mounted perpendicular to the spring antenna, which strongly implied the marking of this "perfect linearity" - but curiously (in retrospect) no video demonstrating it. Christopher has also mentioned many times that he has no musical skills, and so can't demonstrate his creations effectively in that manner.
But none of these circumstances / reasons / excuses prevent him or someone else from conclusively demonstrating this linearity phenomena (if it exists) in a video. Christopher himself has referred to this type of testing as "fist popping" - where the pitch response to the quickly opened / closed hand is examined throughout the pitch field for equivalent relative pitch change, so he knows exactly what I'm talking about. It can be easily and effectively performed by almost anyone, even those untrained on the Theremin and with no musical ability. I recently demonstrated (for a second time) the linearity of the pitch field of my D-Lev prototype via this basic and quite effective technique:
If one were asked to express this in the form of rules:
*Show me!
Absence of evidence isn't evidence of absence, and you can't prove a negative, but given the particulars of this case, if there is no forthcoming definitive video (one way or the other), I will be forced to conclude "perfect linearity" of the spring antenna doesn't exist. Truthfully, I'm at least 90% of the way there and slipping fast, so throw me a bone (if there is one to throw).
