Product Detector FM/AM/SSB schematic..

Hi Dinos,
Harry has described one principle of mixing / demodulation of signals, using non-linear element(s). There is another principle, too, using a four-quadrant multiplier - e.g. a Gilbert cell. IMHO that is the product detector in the narrower sense: a product as a result of multiplying. Search for "Gilbert cell mixer" to find out more.

BR from Ivan

SeAfasia wrote:Hi all,
try to find some explains about product detector circuit how it works inside homebrew receivers..
Any suggestions or articles?
Thanks all..
Dinos

Hello Dinos,
It is interesting that when you "mix" two signal by simply adding them together, then you do not get any mixing products, and demodulation does not happen. This would happen if you simply mixed two signals in a resistive mixer.

A "product detector" is a mixer that uses a non-linear device(s) to distort the signal, such as a diode ring. When that happens the oscillator signal (BFO, Local Oscillator) is distorted by the diodes. Then when you add a signal, then the signal lifts the oscillator signal voltage up and down so that the point of distortion varies with the signal frequency, and the distortion products vary in sympathy with the (weaker) signal. It is the distortion that is the important point since the distortion generates the other frequencies that are created (signal + oscillator and signal - oscillator).

A transistor mixer stage is also non-linear and the signal changes the operating point of the transistor, in effect changing the degree of non linearity. This will give lower mixing products, but the transistor stage also has gain, which overall makes it much better than a simple diode mixer.

Bear this in mind when you look at the links Glenn supplied. He gave three links to very good articles with a lot of detail.

I hope that this clarification helped you?

Best regards from Harry - SM0VPO

A product detector "simply" multiply two signals - one on each input port - and the output is the product of the two signals.

For some product detector info - please look here:

Quadrature FM Detectors
https://www.qsl.net/yo5ofh/doc/fm_detectors/quadrature_fm_detectors.htm

https://en.wikipedia.org/wiki/Product_detector

https://en.wikipedia.org/wiki/Single-sideband_modulation#Demodulation

Hi all,
try to find some explains about product detector circuit how it works inside homebrew receivers..
Any suggestions or articles?
Thanks all..
Dinos