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I have a sinusoidal signal at 50 Hz, that varies in amplitude, with no offset. The amplitude goes from 0 to 5 V (peak to peak), and the amplitude contains all the information I need. This signal will change abruptly (in amplitude) but not very frequently, by that I mean for example that it could be at 2Vpp for an hour and then suddenly change to 3Vpp.

What I want to do is transmit that information using FM. For that to work I will need to transform the signal into something which gives me the same information but now related to it's frequency. For example map the 0 to 5 V range into some frequency range so then I can modulate using a VCO. I would also need to demodulate this at the receptor, and will probably need to remap from frequency to voltage ater the signal is received. This I don't know how to do, so I'm asking for help here.

I don't know if I explained myself correctly, so I'll edit my question if needed. I know that FM may not be the best way to go here, but I have all the components I would need and I don't have the money to buy for some other option.

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    \$\begingroup\$ May we know why you would like to do this? You should be using a peak detector. If you're clever, you can even make it reset on zero crossings. \$\endgroup\$ – HL-SDK Nov 11 '13 at 23:41
  • \$\begingroup\$ I'm using a hall effect current sensor which gives me the current as the signal I described. Yes, I can use a peak detector, and now how to implement it. The issue is that then I will have a DC signal which I don't know how to transmit using FM. That's why I'm asking about translating the amplitude information (or the DC signal from the peak detection) into frequency. \$\endgroup\$ – volotec Nov 12 '13 at 0:17
  • \$\begingroup\$ I think it is often buffered and used to bias a varicap diode in an oscillator circuit. I also think this means you require a superheterodyne receiver on the other end. My knowledge of FM isn't as handy as it could be \$\endgroup\$ – HL-SDK Nov 12 '13 at 0:45
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Both Analog Devices and TI make a variety of voltage to frequency converters - just google "V to F converter" to get several links.

I've used the Burr-Brown (now TI) VFC32 - it does both voltage to frequency and frequency to voltage conversion.

If you are only concerned with the amplitude of the 50 Hz signal, and not its instantaneous value, I would first rectify the signal, to get the peak voltage, then apply that voltage to the VFC.

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  • \$\begingroup\$ Actually transmitting the 50 Hz tone and peak-detecting at the receive end would enable eliminating errors in case the reference frequency of the FM transmitter or receiver drifts. Whether this is overkill depends on OP's accuracy needs. \$\endgroup\$ – The Photon Nov 12 '13 at 0:19
  • \$\begingroup\$ Thanks, I was actually thinking about rectifying. Will read that chip datasheet. Do you know about one I could use to convert from F to V at the receiver? \$\endgroup\$ – volotec Nov 12 '13 at 0:19
  • \$\begingroup\$ @volotec: As I said, the VFC 32 will convert both ways - other V to F chips may do so as well, but I don't think I've used anything else myself. \$\endgroup\$ – Peter Bennett Nov 12 '13 at 0:25
  • \$\begingroup\$ @ThePhoton: I was thinking of doing that but then I thought that I would loose the information through the amplification stages. I actually don't know a lot about communications, but at least that's what it crossed my mind. \$\endgroup\$ – volotec Nov 12 '13 at 0:27

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