Automatic Gain Control

The automatic gain control keeps the strong stations from overloading, and keeps the volume between them all at the same level,  at this point I will reprint the entire schematic because you have built most of it anyway.


Step 1,  Completly remove the detector I told you to build.

Step 2, Build the detector and AGC as in the schematic, but don't connect the 1K resistor on the RF amp; leave it on the regulated V+ . (Notice there is a silicon diode and not geranium, between the PNP and NPN transistors)

Step 3,  Tune a strong channel and make sure the led goes off when a strong channel is tuned,  because of the different tolerances in components, you may have to adjust the 56K and 470K resistors to make it work properly.

Step 4, Disconnect the 1k resistor from regulator (on the RF amp) and connect it to the collector of the pnp transistor behind the tunning LED, the strong channels should now auto level themselves and not overload.

Step 5, Adjust the voltage regulator until the static is present, but does not feed back.

Step 6, Retune the receiver.

If you want to improve the receiver, you can add one or more of these features:

455 KHz hash going into the front end is removed by the 100uh coil, and the two 100 uf capacitors.
The geranium diode balances the oscillator.
The 27K resistor just makes it work on 5 volts without the static being so loud that it gives you a headache.
The positive connection to the gang, and the loop stick, just makes it work with the FM schematic without fire.

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