The Frequency Modulation Guitar Pickup

[Inventor]

So I went back and read the original post that led to the Own Your Tone guitar pickup system, and in the very first post is mention of another pickup system that is worth exploring, the FM system.

Very simple, really. Strings are like FM radio antennas, they resonate electrically at around 100 MHz. Now pluck a string and it's resonant frequency varies with time, following the vibration. This change in resonance is detectable and would provide the vibrational information of the string. Long story short, you get the sound but FM modulated.

Just posting to start a discussion. Positive comments and critiques are welcome and encouraged.

Les

[DrJustice]

I'm not sure I follow this. Where would excitation of the string in the 100MHz range come from, and would a string be able to vibrate mechanically with enough amplitude at 100MHz to generate a useable voltage? I can imagine that at frequencies so far above the strings fundamental frequency the physics might lead to vibrational modes that aren't multiples of the fundamental, but instead depend on the instantaneous tension and length of the string due to its movements at the normal lower frequencies - as if you strike a string normally and then turn the tuning knob back and forth

DJ
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[Inventor]

Well, DJ, I'm thinking of a few different circuit configurations. The simplest one would be to create some kind of wide-band oscillator/noise thingie and attach the bridge to a sensitive node instead of grounding the bridge. Then all the strings together, including their crosstalk and whatever their equivalent resonant response is, would determine where the audio / noise source energy ends up being. OK that made very little sense from an engineering perspective but from the disorganized way that i think in vague terms, I think you can construct in your mind what I meant by that.

Another approach would be to place an impedance, probably a tuning cap, at the headstock location of each string, sum them together at a node and run a return via the truss rod. Then there would be six resonant peaks that could be attached to some excitation circuit.

For the circuitry i'm thinking of something like a wien bridge or similar circuit such as the one i created a few years ago with dual impedances in an opamp bridge to form an oscillator. Other ideas include driving the strings with a strong enough signal that they transmit so that no cable is required to the guitar. Note: there is an existing patent on strings used as antennas.

So there are some formative, disorganized thoughts that we can hopefully use to construct something a bit more solid. Also I did some testing with Dan Minoza in the chatroom last week. He has a cheap fm radio, cheap enough that the tuner is not isolated from the antenna length. Dan was able to select stations and warble vocals on tuned stations by moving or plucking antennas made of guitar strings. That was our first experiment. What do you propose as a second experiment, DJ, anyone?

Les