coil tuning

"Why does it need to be understood? " - Christopher.

For the same reason that everything "needs" to be understood..

If we do not understand the way things work, we cannot use how they work in different applications, we cannot improve the way they work (other than by innefficient "trial and error" methods), we have no way of fixing it when it fails to work, and we will be inclined (due to our intrinsic compulsion to find reasons) to concoct erroneous mystical explanations for how it works.

This is the greatest benefit of the scientific method to humanity - a methodology by which we can examine phenomena (ideally under controlled conditions) and formulate testable hypotheses, then progress to testing the hypotheses and either eliminating them or "verifying" them - always keeping an open mind about the possibility for some other mechanism is behaving in the same way as our hypothesis behaves. When a hypothesis has been "verified" extensively, it can be regarded as a "theory" - but even the most robust theory can never be regarded as absolute.

Having a "working" hypothesis enable us to use the "knowledge" - If we have no hypothesis, no idea about how something works, we have no way of using any mechanism "safely" and no way of using its mode of operation for anything else.

I am probably more sensitive to this matter than most - Prior to my theremin venture, I was "forced" to work in an area where scientific method was scorned by many. My (then) employer took on a commission for a bunch of super-rich (all were in the top 100 wealthiest people on the planet, one in the top 10) people - I did not know about any of this at the time - they were playing a game.. My task was to evaluate "free energy" devices being published on the www, with particular focus on "inventions" by Bearden and the French "research centre" which was funded by some of these rich people.

I started out by doing critical theoretical evaluation of the devices - but was reprimanded.. I was told to build the machines, test them, and improve them without any reference to scientific theory or method.. When I built them and they failed to operate, I had no way of determining why they never operated or if they ever could work, without using science - When they appeared to "work" (as some of them did) I was not willing to say "this works" without evaluating scientifically whether they really worked - So I  "broke the rules" by using scientific method, and scientific evaluation (measuring actual energy in vs energy out in controlled conditions) showed that they didnt actually work.

In the end, I resigned and started my own consultancy business. After resigning I was given contracts by my ex employer to continue evaluation of "free energy" devices, and was freed to approach this research in the manner I chose - In a couple of months I was able to gain understanding of some mechanisms by which some "free energy" devices could work - mechanisms which did not break the laws of thermodynamics!

Fred.

"Another interesting characteristic is that it works or it does not.The phenomenon is like flipping a switch, there is no.."it seems like the linearity is getting better". - Christopher

This is a perfect example of why understanding how it works is important!

One has a theremin with your antenna at home - You want to perform with this theremin in a different environment (club, theatre, whatever) - It works at home, but can you be sure that the "linearity switch" will be in the "correct position" when at the performance venue?

Sadly, this "switch" mechanism (whatever it is) does not fit well with my geometry hypothesis.

"With a theremin transistor emitter having a ~1 ma current flow 10 ma p-p does seem high in the circuit, that is why I enjoy real world wiring and measurement." - Christopher

You are not using equalizing inductors are you?

Which means that the voltage on your antenna will probably be < 30V P-P

When one uses EQ inductors, at resonance, the voltage on the antenna can be >200V P-P.

This explains the difference in your measured currents and my simulated (and on other theremins, measured) currents.

Fred.

Fred said: “If we do not understand the way things work, we cannot use how they work in different applications, we cannot improve the way they work (other than by inefficient "trial and error" methods), we have no way of fixing it when it fails to work, and we will be inclined (due to our intrinsic compulsion to find reasons) to concoct erroneous mystical explanations for how it works.”

Truly words of an engineer, the need to understand all. I like to apply mystical to things I don’t understand as a theremin is to most. Then again it could be magical as it appears to be an illusion. When I watch the finest Thereminist perform on YouTube he is mystical as his precise movements are hidden within video limitation or does he have a way to trick my senses?

The coiled antenna method might be the most marvelous trick I have perpetuated for ten years but a trick that still performs for some undefined reason. The antenna is not mystical rather are the probable odds against how I could gain the knowledge to share it. I ask you before, is mankind the only intelligent life in the Universe?  Now that is mystical.

Today is the 2012 Summer Solstice, how far are you from Stonehenge?

It occurs to me that, due to the necessarily proximate ferrous material, a steel spring would be more like an iron core inductor (i.e. the inductance would be higher if not saturated) than an air core inductor.  Are people taking this into account when pondering the possible influence of the screen door spring on linearity?

OK I'll give it a shot:

L = u0 * (turns^2) * Area / length

where:

u0 = 4 * pi * (10^-7)

Area = inner coil area = pi * (r^2)

length = length of coil

For the spring I briefly played around with (recommended by RST on his website IIRC - Everbilt SKU: 202045460; UPC: 030699155941; $4.58 @ Home Depot; 9/16" diameter x 16 1/2" length, ~600 turns / meter):

length = 0.425 meters

Area = pi * (0.018 meters)^2 = ~0.001 m^2

turns = 255

L = 4 * pi * (10^-7) * (255^2) * 0.001 / 0.425 = 0.2 uH

But the "iron core" formed by the spring itself would perhaps multiply this by 100 (or so, who knows) producing a non-trivial inductance.

There's also the series capacitor feeding it that might play in to the linearity behavior.

RS Theremin, it might be an interesting experiment to replace the spring with a conventional metal tube antenna and various series inductors starting around 20 uH up to maybe 500 uH to see if you could replicate the linearity behavior of the spring.  It might also be an interesting experiment to hook the slightly elongated spring to an LC meter to see what the heck the actual inductance is at various frequencies, particularly the operating frequencies your Theremins typically employ.

Calling all inductor experts: is my analysis flawed?

[EDIT] Edited suggested mH above to be uH (doh!)

OK, I made a clear spot on my workbench and hooked a function generator up to a 0.001uF cap in series with my slightly stretched (~1") screen door spring.  On the scope I'm seeing quadrature at around 960 kHz.

F = 1 / (2 * pi * (LC^(1/2) )

L = 1 / ( (2 * pi * F)^2 * C ) = ~60 uH.

Which is in the ballpark of the back-of-the-envelope calculations above, making the permeability of the spring steel in this configuration 60 / 0.2 = 300 * u0.

Hello dewster, today is a fine day.

Well I was happy, make that .001uf a .01uf or eliminate it and I will be happy.

Also collapse the spring down to 1/2" stretch as there is an insulation coating between turns. Now why it makes the musical scale linear is another mystery!

"RS Theremin, it might be an interesting experiment to replace the spring with a conventional metal tube antenna and various series inductors starting around 20 mH up to maybe 500 mH to see if you could replicate the linearity behavior of the spring."

Why... I need not understand or prove anything. This is a $5 trick, what is your time worth and how much have you used (wasted) doing modeling on this subject?

I think if I was selling screen door springs it might make sense. I am not an engineer and never worked in electronics. My knowledge is kitchen table. That is why I find invisiblejelly and his approach to research interesting.

As an engineer do you need to know the speed of the surface of the earth to enjoy using it? Tell me earths surface speed, relative, within the universe and I will do your experiment. (-'

I do have someone special with an open mind and a fine musician getting ready to validate if linearity has all been my own madness or real, that something to bewilder the minds of the theremins brightest.

What gets me dewster is you need this and you have the darn spring, move your Theremax above 900 kHz with 47 pf caps for C6 & C10 and tune as high as you can. Make the antenna a direct connection to the collector of Q1. You will have the solution and can do math all day to figure out the question!

Now I understand the saying: " You can bring a horse to water but you can't make him drink".

Everyone I am thinking happy thoughts, though dewster may end up in the cornfield.  LOL

Why... I need not understand or prove anything. This is a $5 trick, what is your time worth and how much have you used (wasted) doing modeling on this subject?

Modeling can save tons of time, and can eliminate tons of guesswork.  When I'm designing something I'm always trying to optimize it, and when there are more than a couple of components interacting in complex ways I can't always be sure I completely understand what's going on by fiddling around on the bench.  I don't simulate or do math because I'm in love with simulation and math, I do them for deeper understanding, for peace of mind, and to move on.

As an engineer do you need to know the speed of the surface of the earth to enjoy using it?

If I were attempting to land on it in a spaceship I would. :)  Is using a bit of electrical math (like a coil formula or an LC resonance formula) really not germane when discussing an electrical circuit?

"Everyone I am thinking happy thoughts, though dewster may end up in the cornfield.  LOL"

I've been basically living in the cornfield lately with my harebrained processor design ideas. :)

Hello dewster,

I cannot understand math formula's and use on line calculators to get LC or RC values. Most people reading this post have no idea either:

The theremin pitch field is very gentle.

With respect to you, did you find something occurring here: Resonance?

OK, I made a clear spot on my workbench and hooked a function generator up to a 0.001uF cap in series with my slightly stretched (~1") screen door spring.  On the scope I'm seeing quadrature at around 960 kHz.

F = 1 / (2 * pi * (LC^(1/2) )

L = 1 / ( (2 * pi * F)^2 * C ) = ~60 uH.

Which is in the ballpark of the back-of-the-envelope calculations above, making the permeability of the spring iron in this configuration 60 / 0.2 = 300 * u0.

"With respect to you, did you find something occurring here: Resonance?"

I don't believe so.  Typical antenna capacitance is around 10 pF, which together with 60 uH would give a resonance point of 6.5 MHz.

There are all kinds of resonances though, maybe your antenna is ringing at 6.5 MHz and this is influencing the tank somehow?  (This is why I avoid analog oscillators, particularly the single transistor types.)

Hi Dewster,

Interesting idea (hypothesis) regarding the "virtual" Iron core - and yes, it could increase the effective inductance substantially..

But even this increased inductance does not get close to what one needs for linearization at 900kHz.. Or it doesnt 'on its own'.

I did a quick excel 'simulation' of my multi-antenna 'spiral equivalent' (modified your spreadsheet) - There was some slight improvement to linearity close to the antennas (within 100mm of the front antenna) - But this improvement was purely a function of distributed capacitance (as in, when hand capacitance approached the antennas, the distance ratio of the front-to-back ) antennas became more significant, and this would not be frequency dependent (as in, it would work with theremins operating at any frequency, as it is purely a 'linearization' of the distance-capacitance function.

I think it likely that there is more than one reason or 'principle of operation' applying to this antenna - and one of these is likely to be what you have postulated.

Christopher -

Calm down my friend! No-one here is ridiculing you - if it wasnt for you this antenna idea would most likely be lost in historys murky waters like so many other great ideas!

We all have our part to play in this absurd game we call life - and, to me, what makes life fun is synergy - and for this to work best, people with entirely different perspectives need to communicate with each other sharing a common passion and goal. Ego is the killer of synergy.

And yes, I am not far from Stonehenge - Back in the late 70's  I would go there on this day, camp out with my fellow hippies, smoke grass and eat the shrooms, and be deluded into thinking that I was a wonderful, mystical, spiritual person - Our children ran riot without anyone caring for them, but we were all wonderful parents! (sad LOL).

I still get "mystical" - Every morning when I join (in spirit) with my friends in the trees in their wonderful awakening song, and whistle along with them - I do not know what they are singing, but I do know that its where my music comes from.. The scientist / engineer in me wants to analyse the song (and I have recorded hours of it and examined it) but this does not spoil any of the magic.

The reason why I want to understand your antenna is simply to share and use this understanding to make better theremins. Only a few people are able or interested enough to fiddle about with technology - The majority will never get access to your (Lev's) antenna unless it is understood and made available to them - probably as a retro-fit for the theremin they already own.

I do not understand your lack of enthusiasm, after all the years you have been pushing your antenna idea.. We are taking it seriously!!

Fred.

"is mankind the only intelligent life in the Universe?  Now that is mystical"..

Is mankind intelligent? - probably not compared to the most intelligent life in the Universe!

oops