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As an experiment and for educational purposes, I wanted to build and connect an FM receiver to some old computer speakers via a 3.5 mm audio jack.

So I tried building a circuit like this on a bread board

My FM receiver circuit with pre-amp to 3.5 mm audio jack

Note: The 22pf capacitor on the far left is actually a variable capacitor that I can adjust between 8pf and 40pf. And hopefully, I used falstad correctly to depict my actual circuit.

The circuit on the left consisting of the two transistors is something I found in most FM receiver tutorials. And I figure I couple it to a NPN transistor pre-amplifier circuit on the right. I then connect the output to the tip of a 3.5mm jack.

When I power up the circuit, my speakers are silent. If I touch the antenna with my fingers, my speakers produce a low frequency hum. I disconnected the 3.5 mm jack and hooked up an oscilloscope probe to the output and confirmed there is no signal...in fact I don't even see any noise waveform unless I touch the antenna with my fingers.

Does anyone have suggestions on what I might do next to receive an FM radio signal or at least noise from a blank FM channel?

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  • \$\begingroup\$ So... you are actually trying to build an FM reciever, rather than trying to connect the output of an FM receiver to a computer speaker. Your title should then be "How do I build an FM receiver", which is probably too broad a question for this site. \$\endgroup\$ – Peter Bennett Feb 7 at 2:21
  • \$\begingroup\$ A question here about debugging a circuit would need to include the schematic, component values (and for a radio their type and the overall physical construction) within the body of the post itself, not as a link. \$\endgroup\$ – Chris Stratton Feb 7 at 4:57

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