On the Internet I found FSK demodulation connection diagram with LM565 . And I'm trying to connect up it in Qucs. At the output of the whole schema I get unclear result.
In my previous topic we were able to come to the right decision with FSK generation Topic1. So FSK generator works properly.
I suspect the error is in the circuit of LM565. In many articles there are different versions of internal circuit diagram of IC PLL LM565.
I did as here.
But I don't understand the element that is marked in red.
Look, please, what could be wrong?
Best Answer
The problem is your VCO range is a couple orders of magnitude , your signal shifts maybe 25% and your LPF should reject mixer output (2f) fundamental by > 20dB this below signal excursion and is too close to 0Vdc meaning not centred.
Other than that it’s ok.