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Theremins are based on LC oscillators, using the self capacitance of the external L (antenna) which obviously varies with hand position. So, an RC oscillator (555) is a poor choice. (So is using a crystal oscillator for the reference, as I found. Both oscillators should be similar, so that their thermal drifts are similar. Mine drifted like crazy because the ...

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I donâ€™t have Theremin recommendations at this time but two fingers about a ~ cm apart is 1pF then inverse squared , so change the wire to a small area coil or foil. You can mix 2 100kHz oscillators in a XOR gate or diode mixer. Try that. Capacitance depends area and gap. Then 50pF fixed is about right if the same f. But stray capacitance between sensors ...

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That's just the math behind that kind of mixer. To understand that, you should look at the very common example of why a "zero-order hold" is not an appropriate reconstruction filter for DACs. Exactly the same math applies here: You're producing images of the sampled signal, at regular (sample-interval-spaced) frequency distances. Some of these end ...

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If the devices that you are connecting to are typical, the summer resistor values are not that critical. As an example, here are the impedance values of my Stereo receiver, which I will be connecting a passive summer to the right and left Tape outputs to feed a spectrum analyzer. I haven't picked a value yet, I am working on other parts of the design. What ...

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The first table is only usable at an RF power of -10dBm, and only at an LO frequency of 5.25 GHz. You would expect the power of a 0RF spur to stay constant, regardless of the input RF power, so it's not correct to try to use the first table to take 3.4dB with respect to a different RF input power. Given that the LO to IF isolation is given as typical 32dB, ...

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Use center tapped potentiometers into virtual grounds. something like this: simulate this circuit – Schematic created using CircuitLab dual center tapped potentiometer:

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