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Plz help me in understanding this RF reciever

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It is a regenerative receiver that is connected so it nearly oscillates due to positive feedback through the 3.3pF capacitor.
The transistor is a common-base oscillator, but with not quite enough positive feeddback to oscillate. Its gain at the tuned frequency is extremely high.
It might also be a super-regenerative receiver where a signal causes its output level to build up until it oscillates and it cuts itself off at a fast rate called its "squegging" frequency which keeps its gain at its most sensitive.
Google has many examples of regenerative and super-regenerative receivers.

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The capacitors in the opamp circuit are filters. The larger capacitor following the 100k resistor smooths the output of the receiving transistor to DC. The 1nF capacitor has a small value and smooths the 433MHz but allows the signal's modulation to pass to the opamp.

Look up Super-regenerative Receiver in Google. It is a very simple AM receiver that gets cutoff when it receives a carrier. When it is cutoff, its output voltage goes high which causes the output of the opamp in my drawing to also go high.

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  • 2 weeks later...

If it has a crystal, it is a superheterodyne receiver with local oscillator, typically 10.7MHz.

It is much stable than the super-regenerative receiver.

But I can tell if the layout and circuit is fine-tuned for the regenerative circuit, it won't do any significant differences in performance with heterodyne one.

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