FM Amplifier Circuit

Active FM Amplifier:
Parts List:
     R1 = 27K
     R2 = 270 ohm
     R3 = 1K 

Tr1,Tr2 = 22pF, trimmer cap (15-40pF)
  C1,C2 = 5.6pF
     C3 = 0.001uF (1nF), ceramic
  C4,C5 = 0.01 (10nF), ceramic
     C6 = 0.1uF (100nF), ceramic

     Q1 = 2SC2498, 2SC2570, 2N5179, SK9139, or NTE10. NPN VHF/UHF transistor
     L1 = 4 turns of 20SWG magnet wire, 5mm diameter. (so-called 3T+1)
     L2 = 3 turns of 20SWG magnet wire, 5mm diameter.
With only a small handfull of parts you can built this trusty FM Amplifier.

This amplifier will pull in all distant FM stations clearly. The circuit is configured as a common-emitter tuned RF pre-amplifier wired around VHF/UHF transistor Q1.

All capacitors are ceramic, and 50V is the standard but the 25V types work fine too. Trimmer capacitors Tr1 and Tr2 (22pF) are adjusted for maximum gain.
Input coil L1 consists of 4 turns of 20SWG enamelled copper wire over a 5mm diameter former. It is tapped at the first turn from the ground lead side. Coil L2 is similar to L1, but has only three turns. Pin configuration is shown in the diagram.

Source: "Popular Electronics" magazine, Copyright © Gernsback Publications, Inc. 1996. (Gernsback is no longer in business since January 2000).

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Copyright © 2003 - Tony van Roon