A Simple Reliable Double Sideband Suppressed Carrier (DSB-SC) Demodulator

[ftg]

Thank you for mentioning this project in the sinewave inverter thread, I thought it disappeared with the radio board.
I'll have to dig in my junkbox for some comparators and 4046's to test this out one of these days.

Direct DSB demodulation without costas or squaring loop would be quite nice and the lm339 duty cycle modifier looks like a neat trick for doing it.

[KerimF]

Thank you for mentioning this project in the sinewave inverter thread, I thought it disappeared with the radio board.
I'll have to dig in my junkbox for some comparators and 4046's to test this out one of these days.

Direct DSB demodulation without costas or squaring loop would be quite nice and the lm339 duty cycle modifier looks like a neat trick for doing it.

Lately, to show that this simple topology combines the two known techniques (Costas Loop and the Squaring Loop), I updated the duty shaper (50% to 25% or 75%) by adding to it a similar one but in anti-phase.
Their two open collector outputs are ORed and the result is a square wave signal whose frequency is 2*fc.

I called their block '455KHz_doubler' (its image is attached below).
(This block replaces the first/upper duty shaper on the main schematic which is driven by the DSB-SC signal. The second/lower duty shaper is no more needed, also the anti-phase DSB-SC signal that drives it).

Added:
To simplify the 455KHz_doubler, XOR gates (as of 74HC86) could be used to generate the 2*fc square wave signal.