Gang specifications used in FM receiver.

Thread Starter


Joined Apr 28, 2007

Can anyone tell me about the Gang capacitors used in AM/SW Radio Receivers. Can I use the gang of a AM/SW radio receiver set from the junk box in a FM receiver. Is there any specific parameters?



Joined Apr 20, 2004
The purpose of the gang cap (or gang inductors) is to tune the input to resonate at the desired frequency, and to adjust the frequency of the local oscillator to mix the input signal down to the IF - 455 KHz for AM (although car radios at one time used 267 KHZ) and 10.7 MHz for FM.

For SW, the range is going to be lots wider than for broadcast band AM. Junk box variable caps are not likelt to have that kind of range, although you should be able to switch additional sections in for tuning lower than AM broadcast band. Getting the local oscillator to track could be a trick, though.

The variable cap is tuning a parallel tank circuit. The value of the fixed inductor in the circuit will determine the range of values of the variable capacitance needed to tune the tank to the signals. There will be another inductor asociated with the local oscillator. The section of variable capacitor that changes the local oscillator frequency to beat the input down to the IF will also be determined by the LO inductor.

You might do better going to the ARRL site and finding the schematics for the front end of a SW receiver. Stick that together, and if you can get a signal out, that can be fed to your existing IF amp.