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my FM radio has frequency problems.

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New Member
It seems that I have made the basic wiring required to generate an FM radio signal. Along the way, I have picked up modem signals, and I can barely pick up a station but I couldn't hear (from the announcer) what frequency it was on. I have picked up an FM station before using the same circuit.

The only parts that create difficulty are resistors, and capacitors.

An astable multivibrator (made with two transistors) is in my FM radio. This acts as the radio oscillator. What should the frequency of it be? Also, I have a tank circuit (capacitor and inductor in parallel) which determines (I think the input) frequency.

The first thing I want to accomplish is to have an FM radio tuned to 102.9Mhz. I need to know what frequency I should set the oscillator and the tank circuit so that I can get this frequency.

My radio does not use a mixer.


New Member
Draw the circuit and post it.

We can the see how you have done things.


New Member
(hopefully the attachment system on here works this time)

You should see my circuit below. What I need is at least one equation that uses the values of the resistors and capacitors (that change frequency) in my circuit.

If your equation is right, the answer will be about 108Mhz (108,000,000Hz).



Active Member
Using the values shown in your schematic suggests that the LC combination at the front end resonates a about 93 mHz. Component tolerances as well as the actual installation may shift the resonant frequency. I've no means to post the formula but it's the generic formula for resonance of an LC circuit.
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