optical voice link

[Macgman2000]

Great info, I appreciate the feedback.

Darrel, how is your PCM method different than PFM?

I am using a oscillator with an unmodulated 300Khz pulse train, when modulated it deviates the frequency proportional to the audio amplitude. At the receiver I am using a PLL to pull off the audio from the VCO feedback loop.

Nick

[Darrel Taylor]

I am using a oscillator with an unmodulated 300Khz pulse train, when modulated it deviates the frequency proportional to the audio amplitude. At the receiver I am using a PLL to pull off the audio from the VCO feedback loop.

That sounds more like plain old FM, where you modulate the frequency of a carrier with an analog signal.

With PCM, the analog signal is converted to a data stream that can be stored or transmitted like any other data. The data rate is about 1/10th that required by a direct 8-bit A/D conversion, although the quality isn't quite as good, and will probably never match the quality of your FM system.
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