am rf amp for internal antenna circuit

Posted on Feb 7, 2014

Any NPN transistor can be used. The author used a 2N3904, but a 2N2222A should work just as well. A good, low noise transistor would be even better. Some radios only have three connections to their ferrite bar antenna: the antenna connection to the tuning capacitor, ground (two wires twisted together) and secondary (the smaller number of turns). I

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n this case, treat the twisted wires as ground, and the secondary wire as the base connection to the transistor. The transistor will then receive its base bias from the radio. R1 changes with the supply voltage. If your radio is 9V, use 56K. If it is 6V, use 47k. If it is 3V, use 33k. The goal is to bias the collector of the transistor to one half the supply voltage. The schematic shown is for a negative ground radio. For a positive ground radio, substitute a PNP transistor.

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