The Lev Antenna Revisited

FredM said: What is perfect linearity?

Replace perfect with ideal so this does not become a theological discussion. The linearity is found in the sound byte on my webpage, the lowest octave actually went a little sharp. (using five octaves)

If someone wanted to validate the Lev Antenna, begin with the parameters that have been shown to work.

* Use the proper spring coil with ½” (13mm) stretch, I may send you one.
* The LC tuning on earlier models was necessary, but now… not always?
* Operate your pitch oscillator at 900 kHz.
* Use Hartley oscillators made with NPN bi-polar transistors or vacuum tubes.
* Use ferrite oscillator inductors instead of air core.
* Oscillator LC capacitor = 100pf
* Use a good earth ground!

The Spring = Hillman/Resorte 9/16" x 16-1/2" x .054"
Zinc Plated, stretch 1/2" or "about" 16 turns per inch.

Did someone say the [b]Theremax[/b] might be a good place to start?
I have not tried one but I would agree! Bypass with a jumper wire the C45 5pf antenna capacitor or replace it with a .01uf or larger.

The Lev Antenna can work on the [b]Theremaniac[/b] pitch only theremin, though it may be better to raise its frequency up to 900 kHz. (3 1/2 linear octaves - PNP Transistors)

As of today, the Lev Antenna does not work on an [b]EtherWave Standard[/b]. Once it is better understood it may be adaptable to lower frequency theremins, I don’t know.

On my theremin setup, my hand plays to the center of the spring coil, though linearity is found down at the base of the antenna. There is no critical playing area.

You say do the math, when purchasing a five dollar spring is more efficient than buying a calculator, is this an engineer issue?

[b]Edit:[/b] The linear phenomenon either flips on or it doesn’t, there is no passive "it seems like the linearity is getting better", it’s a startling event!

In the states the spring coil can be purchased at Lowes Hardware (http://www.lowes.com/pd_246623-37672-543011_4294934474__?productId=3115901&Ntt=spring&pl=1¤tURL=%2Fpl_Hardware_4294934474__s%3FNtt%3Dspring%26page%3D2&facetInfo=). If anyone is outside the USA I will send you the spring coil at no cost to you to encourage the validation of the Lev Antenna. (Customs may be a problem?)

[b]Email your postal address to:[/b] theremin@oldtemecula.com

Ruslan,

Until someone validates the Lev Antenna within the parameters I list above it would probably be frustrating to venture outside of them. So the answer is I doubt you could have success with the theremins you mention.

The connection to the antenna must basically be direct with no inline interference from EQ coils, chokes or small capacitors.

Edit: Imagine a new theremin with perfect linearity and the richness in sound found in Clara’s instrument! The mp3 of my design is at the bottom of this link. I can’t play but you get the idea.

New Hybrid (http://www.oldtemecula.com/theremin/tube_valve.htm)

From my coil / transformer reading lately the "skin effect" and "proximity effect" start kicking in at shockingly low frequencies (high audio to low RF - even 60Hz power is influenced if the conductor diameter is large enough, as it often is with AC power distribution; high frequency coils are often composed of Litz wire, a stranded wire with individually insulated strands).  Copper is non-ferrous so it has essentially the same permeability as free space.  But a steel spring would have very high permeability, making the "skin effect" quite pronounced (this is one of the reasons why iron is never used as an AC conductor).  Only the very outer layer would be conducting the AC current.  How thick of a conducting layer is this?

skin depth = sqrt( resistivity / ( pi * frequency * u0 * permeability ) )

u0 = 4 * pi * 1E-7,  For steel the relative permeability is maybe around 75 and the resistivity is 1.43E-7, this gives a skin depth of about 22 um at 1MHz.

If the wire diameter is 0.054" = 1.37 mm, then the cross sectional area is (pi*r^2) = 1.4741E-6 m^2.  The non-conducting central core diameter (a conceptual simplification) would be 1.37 - 0.022 mm, and the area would be 1.4272E-6 m^2.  Subtracting these give the conducting skin area of 0.0469E-6 m^2.  The ratio of DC to AC resistance is therefore 1.4741 / 0.0469 = ~32.

What implications this has in terms of using it as a Theremin pitch antenna is beyond me, but the AC resistance would be 32x higher than the DC resistance, and the inductance would be somewhat decreased.  In addition, the higher AC resistance would lower the Q of the coil by a factor 32 (all @ 1MHz).  The coil properties are clearly less than ideal.  I also wouldn't be surprised if the use of thick spring steel for the windings significantly increases the inductance.

[UPDATE] Just stuck my LC meter on the Lev antenna screen door spring.  Seeing 30.3 uH @ 540kHz & 35 mm elongation.  Inductance decreases with increased elongation, and this is expected due to reduced inductive coupling between the windings with the longer length.  (Interestingly, no elongation measures 32.1 uH.)

So I can see how stretching the spring might alter the null tuning point somewhat, but the value of the inductance is probably too small to significantly alter linearity (at least in the Ether Wave EQ coil sense).

dewster you scared me....The opening of this thread I thought Fred was yelling at me again. LOL

(Interestingly, no elongation measures 32.1 uh)

I have found there to be an insulation coating between spring turns. The phenomena I speak of has a better chance of occurring if the spring is not stretched but the 1/2" I use is for better inner winding insulation. The antenna works if the driving parameters are met.

The antenna always seemed to me as a broad band low Q as it can work between 875 - 925 kHz. The event is startling, it either turns on or it does not, there is no it seems like the linearity is getting better.

Christopher

My theremin journey has always been about the antenna, why I don't know. We all have demons that pursue our attention, mine just happens to be one with a Russian accent. (-'

"The antenna always seemed to me as a broad band low Q as it can work between 875 - 925 kHz"  - RS Theremin

F = 1/(2*pi*sqrt(L*C)).  30 uH and 8 pF (approx. antenna capacitance) gives ~10 MHz.  If something is going on here it probably isn't simple resonance. 

The "proximity effect" tends to push the conduction area to the inner sections of a copper coil, not sure how that might be distributed given an iron coil.

Also in a copper coil, the inductance and self-capacitance are strongly correlated to wire length, which makes sense because it's essentially a wave guide.

First - Just in case anyone thinks I dug this ancient thread up - I DIDNT! - It wasnt me, gov! ;-) But as its here, and as my will is too weak to stay away from TW...

Let us, for sake of getting a "starting point", assume that the iron spring has SOME effect on performance - it will have, even if for no other reason than that by changing its tension one will change its capacitive relationship in much the same way as changing the length of a telescopic antenna changes its capacitance.

Now if we do even the most exagerated evaluation of the spring antenna, and try to find a mechanism by which it could operate, we (or at least I) do not find any - I certainly do not find any based on the capacitive mechanism by which I believe theremins work (and which is how Lev and Bob believed it works, and is an explanation which is backed up and entirely explained by known physics and predictable and verifiable with mathematics, and which, other than for strange unverified apparatus, is entirely duplicable).

Theremins such as the Theremax and EPE which are NOT designed for inductive antenna equalization (The EPE-2008 did incorporate an antenna equalizing coil, but this was simply tacked onto the SC front end and DOESNT WORK - simply because the tank is designed for direct capacitance sensing and was not altered to make it suitable for being driven by an antenna resonant circuit - see my addendum below) require a MUCH larger  antenna inductance than could ever be provided by a spring antenna, and modified tank circuit.. On theremins which are designed for antenna equalization, the extra 50uH or so provided by the spring antenna is less than 1/100th of the required equalization inductance, even running at 1MHz.

So the only way that I can imagine the spring antenna achieving the claimed linearization, would be through some unknown mechanism -

But heres the problem..

The "The Lev Antenna" has nothing to do with Lev - Lev didnt use spring antennas, he used resonant antenna circuit with equalising inductance working into antenna capacitance, and he used a series resonant tank with the "virtual inductance" created by variation in capacitance seen by the antenna imposed across one half of the coupled (balanced) tank inductance - This topology has been misunderstood or ignored for decades, with people proclaiming that the Lev theremins used a parallel tank circuit in an Armstrong configuration. Almost every theremin not designed by Lev has copied this misconception, and been based on parallel tank topology.

Lev did not design high frequency theremins - He did not use spring antennas - And he got good linearity.

The statement "Until someone validates the Lev Antenna within the parameters I list above it would probably be frustrating to venture outside of them." Is the hub of the problem.. We would all love to have a simple method of getting perfect linearity.. But any theremin needs to have reasonably consistant performance. With (as I stated in my initial posting here) a given set of environmental factors (including the "right" placement of grounded surfaces etc) it is possible to get linearity from even the most basic theremin - One can even arrange an array of conductive objects and strategically place these to alter the shape of the field, to improve playing field linearity..

But the above is no good for a practical instrument - One needs an instrument which works with reasonable linearity at least, even in non-ideal situations.

As for "Until someone validates the Lev Antenna within the parameters I list" this begs the question as to why, with so many people having attempted to get linearity from your antenna, within your parameters and following your instructions, over so many years, no one has yet "validated" it.. I am not saying that you are being untruthful - I believe that you believe you have seen perfect linearity - but it seems that no-one has verified this yet.

Fred.

Addendum: Below is part of an email reply to a friend:

The question of “coils and how they interact with the antenna and their playability “ is a deep one – As you know, I am not into “dark arts” LOL ;-) – But the whole nature of the front-end interactions are about as close to “dark arts” as one gets in electronics..

The reason for this is (I think) that the primary mechanism is extremely complex, even if one has ideal components – the math’s is on the edge of my ability to deal with (in fact, I can only compute linearity by using a basic macro within excel, which iteratively seeks the solution – this is effectively running a minor simulation, and takes calculated capacitance values from the distance table and works out the inductive loading effect on the tank inductor caused by the position of the frequency with reference to the antenna resonant frequency – I am not at all confident that it is accurate) – The effects of coil SRF / Capacitance / couplings etc have a huge effect on real performance – sometimes beneficial, sometimes detrimental.. With crudely hand-wound coils, even though I have taken care to make them as similar as possible, I have never managed to wind two equalizing coils which behaved identically!  - This is why I have now standardized on the Bourns / Miller 6300 series – They at least have repeatable results!

Tacking an equalization coil into a theremin which is not specifically designed for equalizing inductance, from my experience, never gives good results – and sometimes has disastrous results.. The most classic case of this was the EPE-2008 theremin – A SC theremin front-end was used virtually without modification, and the results were much like you describe – the “ the weirdness that I felt between zero feild setting and the antenna might be translated as moving my hand through water rather than through air” is almost exactly what xxx said to me when I tried to linearize his xxx  (based on the SC)  xxx and I had a hell of a job linearizing my theremins which were at the Royal Festival Hall – They had S/C oscillators – I ended up modifying them during the show (I had 3 I had modified before the show at the last minute, but ran out of time to complete the others – As I see it, the primary difference between “Equalizer friendly” and “Equalizer unfriendly” designs is this:

An “Equalizer unfriendly” design (as in, direct-to-antenna friendly) tends to have a larger tank inductance with a smaller tank capacitance – the antenna capacitance is in parallel with the tank capacitance, and the oscillator frequency is simply determined by the sum of tank and antenna capacitances in parallel with the tank inductance… In the case of the EPE / SC theremins using a 455kHz IF Transformer, the tank inductance is 680uH and the tank capacitance (inside the IFT) is 180pF. It can be seen that a small change in the capacitance (due to antenna capacitance) has a significant effect on the oscillator frequency.

An “Equalizer friendly” design operates in a completely different way – One is not looking for change in capacitance across the tank capacitor (in fact, one wants to eliminate this) one is looking for a change in inductance across the tank inductor as the means of changing the oscillator frequency.

A correctly tuned antenna circuit represents an inductor connected to ground, the inductance (or “virtual inductance”) is controlled by the capacitance “seen” on the antenna.. As this inductance is in parallel with the tank inductance, when it decreases, the oscillator frequency increases – and visa-versa ..

The “Law” or “conversion factor” between the change in antenna capacitance and the change in total tank inductance is what imparts improved linearity – one can get an idea of this if one looks at the relationship between XL and XC on a standard frequency plot – one is linear, the other exponential – doing this strange equalizing trick one is effectively taking the linear curve and transmuting it to an exponential curve, and this exponential opposes the natural square law curve, resulting in an approximately exponential result.. And an exponential curve gives a musically linear response! … ;-)  … Oh, I am sure some mathematician would have a field day tearing my explanation apart – but it works for me! ;-)

The  “Equalizer friendly” design requires that the “virtual inductance” has a significant effect on the tank inductance, so the tank inductance is reduced (100uH in the case of the EW) and the tank capacitance is increased (3300pF in the case of the EW) – it can be seen that the tank capacitance is huge by comparison to the SC type designs – to modify a SC for operation with a linearizing coil, one needs (among other things) need to decrease the inductance an increase the capacitance..

The role of the tank capacitance in an “Equalizer friendly” design is to set the oscillator frequency and not to vary as a consequence of  changes to antenna capacitance – changes to antenna capacitance should only alter the tank inductance by merit of the “virtual inductance” in parallel with it.

There is also a huge “multiplication factor” involved in the conversion from capacitance to inductance – this multiplication factor (of sensitivity) is a complex interaction of the antenna equalization components and tank component values.

Which brings us back to the “mish-mash” behavior where Equalizer and tank component values are not carefully selected – A number of strange (and sometimes destructive) things can happen –

1.) The performance is critically dependent on the operating point of the oscillator / Equalizer -Antenna tuning .. Most theremins tune the null point by changing the reference frequency, so the real Equalizer -Antenna tuning varies and is not constant..

2.) Close to resonance (hand distant from the antenna) high currents can flow, and the virtual inductance can reduce to extremely low values – this can shunt the tank inductance, cause the oscillator to stall, and even blow up transistors.

3.) Tuning so that antenna resonance is never close defeats the whole object, linearity returns to equal or worse than an un-equalized configuration, and sensitivity is reduced.

4.) Both antenna capacitance and virtual inductance can be “seen” by the tank, causing cranky operation.

Fred thank you for the last pcb referral, it is too good to be real as I picture small children in China stirring vats of chemicals. I placed an order, will see how it goes.

You said: "The "The Lev Antenna" has nothing to do with Lev - Lev didn't use spring antennas"

Lev Sergeyevich dabbled with the same electronic components we did right up through the early 80's. There is no component on my circuit board he was not completely aware of, why would I waste my time trying to promote fake theremin knowledge for 10 years? I have nothing to sell or prove. You need to get your operating freq up to 900 kHz before turning into rubbish... knowledge that might just be sacred. (-'

What are the odds of someone never involved in the electronic field and never looking how a theremin is constructed designing a beautiful working model? Would you call it luck or genius? We both know it  takes something more!

Christopher

Chris, First, good luck with the PCB's.

I dont want to get into any argument - I have an iron spring (almost exactly) to your specification, I have run tests on this over a huge frequency range including exactly the frequency range you specify - I have not built a fancy wooden frame or duplicated your expansion method, mechanical stuff is not my forte, but used rope and a pulley attached to a supporting beam on my sheds ceiling to adjust the tension.. I have also wound spiral antennas on plastic tubes and used both copper and steel wire, and run oscillators and driven signal generators and done spectrum plots..... Yes.... Like you, I am, at times, not entirely sane! LOL ;-)

And I found nothing.

Which does not mean there isnt anything... I spent 3 years and bought large blocks of horrendously expensive special ferrites to build and test "free energy" devices expounded on the web by people who I thought were charlatons - but I was funded to do this research, was able to reclaim any money I spent, was able to pay to get coils wound and hire equipment such as calorimitry chambers and the like.. Nothing gave "free energy" -

But I did discover a mechanism wherebye "free energy" was theoretically possible - and which may account for some of the positive results people have found - This "free energy" was within the bounds of the fundamental laws of physics (as opposed to being zero-point or vacuum energy, or any of the other pseudo science BS reasons given) - It was simple thermal energy - and understanding how to extract this energy (as in, there does seem to be a possibility that by synchronising the loading of coils in some wierd configurations round some specific ferrites, one can convert thermal energy to electricity, and this extraction process causes the ferrite to cool) is the next challenge, even if only to invalidate my hypothesis (which was based on extremely flimsy results where measurements were only a tiny amount over the noise threshold and only just into the area where it statistically became noticable) - But the physics for this (if true) is beyond me - and my client has taken my data and hopefully it will be explored to conclusion..

Why was I given the above job? - Quite simply, because I am known for being solidly rooted in science - But, I am also known for being a heretic.. At meetings, I will voice the most "absurd" ideas, postulate the most outlandish hypotheses, and am willing to explore anything to almost any lengths... Although I did try to get out of this particular task ;-) 

Being truly "grounded in science" is not a "faith" thing - It is a "thought process" thing - Real science starts with the understanding  that there is no certainty about anything - every bit of knowledge, the results of any and every experiment, the "laws" and "theories" - EVERYTHING could be entirely "wrong".

But the theories do give us tools to work with, and "laws" which are "fundamental" - And if something does not fit with the fundamental laws or appears to contradict the established theories, it is ALMOST certain that the error will be with ones experimental methods, or that one is misunderstanding the process (as in, looking at capacitance rather than body temperature ;-)

So the fact that neither I (nor, it would seem, anyone else) have  been able to replicate the results from your antenna does not mean you are "wrong".. And if you are not "wrong" then there must be a REASON why, in some cases, it works.. We have gone over this before and you got angry... "Why do you need to understand" being your cry... And again I give you the REASON why understanding is NEEDED... ITS NEEDED BECAUSE THE REASON WHY YOUR ANTENNA DOES NOT WORK FOR (at least) SOME PEOPLE NEEDS TO BE UNDERSTOOD SO THAT THESE PEOPLE CAN GET IT TO WORK!

Thats why!

For me though, I will not be spending any more time on your antenna - I think (in fact im sure) that you believe in it, but I would be extremely surprised if there is any objective truth in it.

Fred.

" why would I waste my time trying to promote fake theremin knowledge for 10 years? I have nothing to sell or prove. " - Christopher

Probably because you believe what you are promoting is the truth, and for other deeply embedded unconcious reasons (you are deluding yourself if you really believe your "or prove" ;-) - Hey - You are not alone! We all have our matrix which causes us to hold our particular beliefs, to behave in our particular ways, and the resultant "motivations" drive us to do the things we do..

Let me share my dillema with you - A large "chunk" of me doesnt want to talk to you at all - wishes you didnt exist (if you do exist, LOL ;-) and is / was completely outraged by the recent issue which I wont bring up again..

But I know that you had no choice but to do what you did, and say what you said - Likewise, I had no choice but to feel the way I felt and to react the way I did.

My dillema is that I cannot actualy function with this knowledge - Every social construct, every feeling, every way of relating, is based on the delusion of free will and choice - And being aware of this delusion removes any basis for anger or passing judgement or, well, anything.

Hell - I need a long holiday (possibly in some asylum.. ):

Hi all,

"or prove" ;-)

The only answer I have as to why no one has reported back with their results of the Lev Antenna is the fact that this is their first theremin build and they accept the fact that the ideal pitch response they are experiencing is what's normal. I did not fully understand how good perfect pitch field linearity was until I purchased a nonlinear EtherWave standard.

I will have circuit boards available in a couple of weeks, FREE, to anyone that might want to pursue my theremin approach. This will be the pitch side to test the antenna, the full build is also available. I might even throw in the infamous antenna spring if you don't have access to one. All of the board components you purchase yourself from Mouser. This can't be built with junk in your parts drawer so get that out of mind NOW, every component has a specific value and purpose. This is not a beginners electronic project so I would like to know your hobby background.

One thing not mentioned in the linearity experiments is my size at 290 lbs (college football). Maybe I make an above average excellent ground, I spent a  lot of time eating grass. LOL

Christopher

Edit: Don't worry as the response to this offer will most likely be about one person. The era of innovative youth exploring the archaic electronics of their grandparents is an era gone by.