I have implemented an ASK modulator and demodulator pair. The modulator works fine, but the demodulator is giving a vague output. Below is the image of the whole circuit and the simulation output.

enter image description here

In the below output, blue is the carrier of 27 MHz, red is the digital wave of 150 KHz, green is the ASK output and yellow is the de modulator output.


I am not much of an electronics guy, so not good in tuning the circuit. Please help me achieve the desired output so that the yellow wave resembles the red digital wave.

EDIT 1 -

After trying many combinations of R11 and C2 values, finally i got one that is sending considerable voltage into demodulator. The output is still a straight line but its non zero this time.

Here blue is the volatage after the R11 and yellow is output from demodulator. enter image description here

  • \$\begingroup\$ explain how the circuit works. \$\endgroup\$ – analogsystemsrf Apr 5 at 15:36
  • \$\begingroup\$ Hi. I don't have much of domain knowledge. I just replicated the circuit from pyroelectro.com/projects/pyro_rf_receiver_27mhz/index.html. They have also provided explanation (which ofcourse is out of my scope) \$\endgroup\$ – It's a trap Apr 5 at 15:40
  • \$\begingroup\$ Great gravy. I said a "largish" resistor. I didn't say "replace the wire with a nearly open circuit." Reduce it to something reasonable (several kohm) and make C2 larger (nanofarad range.) Do you know what a high pass filter is? Look it up. C2 is just too danged small if you have any kind of load on it \$\endgroup\$ – JRE Apr 5 at 15:42
  • \$\begingroup\$ @JRE i replaced with nano cap and 10k res, but the yellow output is still similar \$\endgroup\$ – It's a trap Apr 5 at 15:47
  • 1
    \$\begingroup\$ You have a simulator there in front of you, and a possible problem with C2 and R11. The demodulator will need some current to operate - 10k may be way too much. Lower it. It costs nothing to run the simulator. If you lower R11, and the "transmit" signal wimps out, increase C2. Prove to yourself that the demodulator doesn't work at all: C2 at like 100nF, and R11 just a piece of wire or a less than 100 ohm resistor. If it still just gives a bump, well now you know the demodulator is really not doing much. \$\endgroup\$ – JRE Apr 5 at 16:40

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