Superimposed differential signal

[man_marius]

I have a system that communicates by a differential signal, that is a superimposed signal of 4 different frequencies, say  f1,f2,f3,f4. These frequencies are amplitude modulated, How can I design a system to translate this differential signal into voltages f1->v1, f2->v2 ... f4->v4 simultaneously. The input differential signal can sometimes contain some of the frequencies, but not all.

My theory is to have four narrow band filter in parallel each filtering one signal, can that work?

[moffy]

Yes, if followed by a peak detector each. Or have 4 multipliers each fed with only one of the frequencies then low pass filter the output. Be aware of aliasing in your design. Look up amplitude modulation demodulation, should help.

[man_marius]

What is easier to implement, the analog filters I have an ideal on how to make them, but it is a bit complicated because of the narrow band (or high Q factor).
On the other hand, the demodulator seems easy but I am not knowledgeable in that field

[macboy]

Is each frequency actually fully AM modulated or just OOK (On/Off Keyed)? The latter case is still technically AM (at 100%) but is much easier to decode.

[man_marius]

Its is fully modurated not only OFF/ON

[moffy]

The MC1496 multiplier is cheap, but requires a few passive components. The BW of the low pass filter is effectively your Q and easy to set.