Pirate Nation Radio - 10 Watt FM Amplifier
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Description: Hello home builders, here is a 10 watt amplifier that has about 10db of gain,
suitable for a .5 to 1 watt FM transmitter. The transistor is a NTE345, available at almost any
electronics parts supply house. This generic design is from the ARRL radio amateur handbook for 2 meters
and the coils have been changed for the lower operating frequency range of 88-108 Mhz.
Construction: The unit is constructed with copper clad board, a large piece is used as the construction surface and is mounted into a case. A hole large enough for the transistor's case is drilled in the center. Other board material is cut into small pads, then glued to the construction surface for part connections. A heatsink is needed for the amplifier transistor, as it is a stud mounted device. Up to 30 watts output is possible with this amp, but for continious duty only 10 watts maximum output is recommended. A fan is required and one came with the "cpu" heatsink that was used. The choke RFC1 and RFC2 are 5 turns of 30 awg wire on a larger (large enough to get 5 turns through) ferite bead of type 43 material, they are not critical. RFC1 keeps rf off the dc line and RFC2 protects the transistor base from over voltage. A 3 amp 3ag fuse is part of the dc power cord assembly. I used SO-239 coax connectors for input and output, however BNC or F type connectors would be fine too. This unit has no swr protection and requires a 50 ohm antenna, do not operate the amplifier without a proper load. Do not omit the low pass filter, the info is here 
10 watt amplifier, note low pass filter on bottem right. Tune up and use: In order to make the amplifier operate properly, it needs to be tuned. To start, set all the trimmer capacitors to middle position, connect the rf out to a wattmeter/dummy antenna, apply power and drive from the exciter then tune for maximum output. Limit your drive to 1 watt maximum. If you can measure the amplifier transistor's current, then adjust for minimum current at maximum rf out. 
10 watt amplifier. - DJ Pirate Joe |
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