FredM - This is Wierd

I answered on the bottom of the webpage so you have the graphics and sound available. And yes the 5.5 wav file opened in Audacity will clearly demonstrate a 1 hz roll over. I will post my reply here once you find and open the 5.5 meg wav file.

This is Wierd  heterodyne behavior and very interesting.

Fred you might copy your text to this thread.

I will try and get a graphic of the board layout posted.

Christopher

>>"Fred I need your opinion of this webpage. You will think I am making this up?"

Christopher, I certainly dont think you are "making this up" -

But I am at a loss to explain it in any way - and I do not understand some of the things you are saying:

>>"On the oscilloscope I see a 30 kHz carrier frequency taken from the normal theremin audio output jack" "The 30 kHz frequency passes right through the detector detector as if it did not exist."

Here is where my misunderstanding starts - unless you are a dog, I do not see 30kHz as "audio" (LOL) - and I wonder if "The 30 kHz frequency passes right through the detector detector as if it did not exist." is actually caused by this 30kHz being remoned by the filter which usually follows the detector.. If it was some 'noob' posting this, I would assume that this was the case, but as it is you, I think I must be misunderstanding something.

So, my first question is: What frequencies are the oscillators running at, and therefore what is the actual difference frequency you SHOULD be seeing from the detector?

>>"The heterodyne method I am using is so responsive that you actually pass through several Null points reaching toward the aerial. There is one dominant range or field of notes, that is what I tune too. The pitch field still behaves mostly as would be expected."  

This "pass through several Null points" leads me to believe that you are seeing the effects of harmonics from the two oscillators interacting with each other - that, perhaps, the strength of these harmonics is sufficient to mislead you about where the 'true' difference frequency really sits.

Alternatively, is there some other source of signal which is being unintentionally mixed, and producing (probably from its harmonics - and if the unintended signal has a square shape, these will mainly be odd - as will your oscillator harmoncs if they are clipped, giving a whole series of "null" points) these "multiple pitch field shadows heard as background birdies".

So, these are the 'conventional' type of explanations I can think of - other "conventional" explanations would include measurement error - you show a "carrier" at 30kHz, which is what I really have a problem with - where is this "carrier" coming from if the oscillators are running at about 850kHz? - Is this "carrier" the result of one oscillator running at (say) 850k, and the other running at 880kHz? ... If this is the case, and your soundcard is sampling at 96kHz, then all hell will break loose and you cannot believe anything you see or hear!

But all the above probably comes over as disparaging, and this is not my intent - I am just stating the obvious, which I feel sure you must have looked at.. I just have a real problem understanding what you are saying on this page! I show some of the things I dont understand (and this may well be because my brain aint functioning as well as it once did, LOL):

>> "There is no Null Point, going below the lowest frequency 1 hz  the field just reverses and the pitch rises, this can be seen at the beginning of the 5.5 meg wav sample above spread out in Audacity. Amplitude is unchanged throughout the range."

Where is this 5.5M, and how do you view 5.5M on a 96k sampling scope?

How are you resolving the frequency down to 1Hz? I cannot do that with a pile of sophisticated equipment (including HP analogue frequency descriminator).

The main problem for me is what you mean by "carrier" - is this actually a "carrier" formed from the difference frequency, and are you looking "inside" this carrier for other signals?

You show a clean 263.1Hz triangle wave, and you say " The sound card inputs the 30 kHz carrier frequency and may be giving a misrepresentation of the wave shape, but I don't think so. This can sound like a  breathy flute, the wave shape indicates odd harmonics!"

Are you REALLY feeding 30kHz into your your sound card???

EDIT >>

One obscure, “off the wall” idea I have just had (and this does not eliminate my other questions) is this:

What if, your difference (carrier) frequency is 30kHz, and the oscillators are distorted producing lots of HF harmonics (or, probably more likely, there is some other interfering signal) and your hand is acting to attenuate these harmonics – as in, your hands capacitance is acting as a variable low pass filter..

This may cause you to see ‘linear’ frequency change on these ‘embedded’ waveforms – what you should (?) see is “steps” in the frequency of the ‘embedded’ waveforms as higher harmonics are attenuated and the lower harmonics become predominant.

Look – there are lots of flaws in the above hypothesis – and lots of possible complications due to how you are viewing the waveforms and the (probably likely) misleading “information” being displayed.. but I float this idea anyway.

Fred.

Ps - If we get into further discussion about this, perhaps we should move such discussion to some relevant topic.. But, unless there is new information, I dont really think I can contribute any more (anything) on this subject, much as I would love to - I like to think of myself as an open-minded person + engineer, but I am probably not that open-minded in reality, LOL!  ... I think sometimes one can get too open-minded and all ones brains fall out! ;-) I am, as you know, absolutely convinced that capacitance is the primary principle on which theremins operate, and that there must be some capacitive mechanism by which the Lev antenna works - This kind of thinking (whether wrong or right) does influence the way I view what you raised on your web page.. You are (it seems to me) seeking exotica and 'wierdness' and have a much more 'artistic' way of exploring circuits - I am always boiling things down to their core components and mostly working within the engineering disiplines which have solid basis in physics.. I DO accept that there are many unknowns in physics, and I will even accept that some of the fundamental laws are flawed, and for this reason I keep an open mind on anything that those who step outside into "pseudo science" come up with... But, in the main, I am not able to step into and explore "pseudo science" - I am not equipped to do so - perhaps I limit myself because of this, but I cannot spend time looking for a complex reason for some event, if a perfectly satisfactory simple reason exists.. Occams razor - But Occams razor has been called "Occams lack of imagination" by some!

Sorry Chris - I presumed when you were talking about 5.5meg you were talking bout 5.5MHz - Duh!

I, too, will blame my meds! ;0) - I have been told that the meds I will be given for my next procedure are extremely pleasant "better than any drug, legal or illegal, that you have ever expierenced before" LOL..

Wonder if I could sue them if it turns out not to be true?

This "pass through several Null points" leads me to believe that you are seeing the effects of harmonics from the two oscillators interacting with each other - that, perhaps, the strength of these harmonics is sufficient to mislead you about where the 'true' difference frequency really sits.  This is possible but does not explain the phenomenon's occurring.  This unusual oscillation kicks in while tuning the LC oscillator coil.

Not saying that's what's happening here, but soundcard inputs can get pretty lame (alias) with large amplitude high frequency signals. 

RS Theremin, do you not have an oscilloscope?  They are quite inexpensive these days and IMO indispensable for this kind of work.  I'd recommend an inexpensive Chinese model with frequency measurement and FFT.  You're really flying blind without one.

Chris,

What about making a LPF with roll-off at (say) 10kHz, and feed your 30kHz "carrier" into that before you take the signal to the sound card.. The "signal" amplitude would probably be greatly attenuated, but if it is the result of heterodyning, should be audible.

If it is FM (and I cannot see how!) a simple PLL can be used to demodulate this - A CMOS 4046 with its VCO set for a centre frequency of 30kHz, and its VCO out (pin 4) connected to comparator in (pin 3), signal in to pin 14, a resistor (R) between pin 13 (phase comparator 2) and VCO in (pin 9), and a capacitor (C) between VCO In (pin 9) and ground (VSS).. R and C form the filter time constant, keep R above 1k, and select C so that you get about mid-rail voltage on pin 9 when you feed a 30kHz square wave into pin 14.

Now any FM should appear demodulated on pin 9 as the PLL locks to the input frequency -

Spreadsheet, DOS program and data for the 4046 can be found here on Element-14.

Hey dewster I could tell from the video you don't look like Frankenstein!

Of course I use an oscilloscope. This is not a project that I plan to pursue but it is worth mention in a week everyone is sharing different approaches of what they are doing in theremin research. The 30 kHz carrier is present at the detector and the audio output at 2v p-p. On a real oscilloscope you can see the carrier compressing (freq raising) as the hand approaches the antenna. The amplitude of the carrier remains constant 1 Hz to 5 kHz.

"Got up at 5 am (like Fred, no he does not sleep)" ..

Oh, I certainly do sleep! Mostly in stretches of about 3 hours, and these can occur at any time of day or night.

I have just come out of a phase where I was asleep most of the time, awake for about 8 hours a day at most.. New meds have improved matters greatly, I now have some iron in my blood! (and possibly a little more blood..)

"On a real oscilloscope you can see the carrier compressing as the hand approaches the antenna. The amplitude of the carrier remains constant 1 Hz to 5 kHz"

Looks to me that the most likely cause of what you are exploring is embedded deep within the filters and sampling 'quirks' of your sound card, and that, without exploring the circuitry of you card and applying the relevant theory, you have no chance of discovering "why" or "how" of what you are seeing.

And what you are seeing is not "reality" - it is as much a function of the circuitry in your sound card as it is a function of the circuit connected to the sound card - you will only understand what you are seeing when you understand the whole system..

A bit like feeding a radio signal into an analogue television set - the patterns on the screen convey absolutely no useful information until you ubderstand how both the radio and the TV work.. Once you understand both intimately, you MIGHT be able to use what you see for some purpose, but even then, it is unlikely!

Subject of Interest Here  

FredM said: “This "pass through several Null points" leads me to believe that you are seeing the effects of harmonics from the two oscillators interacting with each other - that, perhaps, the strength of these harmonics is sufficient to mislead you about where the 'true' difference frequency really sits.”

dewster said: “Just thinking out loud, but I wonder what the phase noise of the 4046 VCO is?  It's almost certainly much worse than that of an LC oscillator.  Not saying it's a show stopper for this application, but it could add significantly to the noise, making the SNR worse.”

Added noise would be a fatal flaw in this experimental approach.

This got me to thinking about Frequency Modulation; IMHO, this is where the amplitude of an audio signal varies the carrier frequency. One might think of it as embedded. This is not happening as I think about it.

When Fred writes he is all over the place when he thinks which reminds me of my once youthful mind. Somewhere in the web he spins is the answer and the rest may be moths and flies.

I think Fred swatted it out of his web with the idea of Harmonic Modulation, not quite those words but this might be correct. The pitch oscillators were probably tuned 30 kHz apart and over-driven. I don’t have it set up right now but an active LPF, which is low pass filter on the first OP feedback, may give good results.

Harmonics are not misleading me rather trying to show me something and anyone else that still has a sense of theremin adventure!  We are all part of a fading culture.

The extreme Pitch field response is what makes all this interesting and a “place” that needs to be revisited.

Not that place down below.

Fred, the thing I don’t like is scopes when they burp a little air into the brown balloon to get a better view. Did you ask for a video recording of the event . . . talk about vacation movies, these are great for parties! (-'

Christopher