"You can hear the effects of the noise in this video..." - Livio
"Did you keep the tank capacitors about the same? By this I mean: is the sensitivity and antenna voltage swing very low like it is on the Open.Theremin oscillator?" - Dewster
The frequency shifts you hear in the video are produced by the 4069 noise that changes continuously the input voltage of the input P and N mosfets. So the frequency produced is not stable.
Then when working at long distances our linearizing software amplifies by a very large rapport the frequency changes and the little instabilities can be heared as in the video.
The antenna is not important in this, removing the antenna the noise is always present, because generated by the oscillator components.
I have seen your original oscillator in your video and it appears perfectly stable at 1 meter with a frequency generated of about 1 Hz, But with 1Hz it is impossible to hear little frequency changes. Can you please test it making the zero beat at 1.5 meters and then, nearing the hand to 1 meter, produce a note of about 100 or 200 Hz. With this note you should hear the noise effects.
"livio, I'm curious. You give good advice when you say stay out of the AM broadcast band - have you have bad experience with this? Not saying your oscillator is bad, just wondering if AM broadcasts have given you trouble that you can discuss here? I mean, is your advice general good practice, or is it from personal experience? - Dewster"
The 4069 (unbuffered) oscillators used in some installation like the first "Tiktaaliik" (1998) was working very good in my little town (Bollengo). But, when going at the museum in Torino we had many problems. The skeleton was sometimes moving by itself. (Torino is a big town and there are many RAI medium waves transmitters. RAI is Italian Radio and Television organization)
Our old 4069 oscillators frequency was about 900 KHz. In the middle of the Medium Wave band. The problem was completely corrected changing the oscillator frequency (if I remember well the frequency was lowered by about 100 KHz, or maybe a little more...)
In the 2005 we changed all the Tiktaalik electronics with a early version of the Theremino System with CapSensors modules working at 2.5 MHz and now the AM broadcasting problems are completely solved. And also the skeleton movements are more fluid and stable.
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Your research on best circuit configuration is really important. I will help with new simulations and ideas.
The DewsterV2 is not convincing me, because of:
- too much components (1)
- components (like Operationals and Dual in Line or SOIC inverters) that impose long and mazy PCB tracks (2)
- too much inductors (3)
- lack of the input isolating capacitor (4)
(1) My experience says that in the front-end circuits all must be minimal. With few and very short connections.
(2) Using operational amplifiers or CMOS inverters, the PCB tracks become mazy and long. With many and long connections (more than some mm) the circuit becomes a radio receiver, can be unstable and can even stops to oscillate because of the stray capacitances.
(3) I could be wrong, but seems to me that the phase shift produced by the second inductor, could be best obtained with capacitors and active inverting. Yes the secon inductor produces a low pass effect but the same integration can be done in software (or firmware) and if done in software we have more control on it. Without the second inductor the number of hardware parts is reduced, the lenght of the PCB tracks is reduced, the noise is reduced etc.. All the functions that can be done in software must not be done here.
(4) The input isolating capacitor is important, maybe you could raise it to about 33 pF (if inductor is 330 uH) but not more or the 50Hz becomes to be a problem in some difficult ambient.