RF power amplifier 80W by C2782

This is a pretty conventional design, using bipolar transistors in a tuned class C circuit. Thanks to the use of two stages, the amplifier can be driven to full power with less than 1 watt driving power, so that a large gain margin results in this transmitter.

Bipolar VHF power transistors have a severe affinity for low frequency self-oscillation. To obtain stability in this amplifier, I employed several techniques, such as placing the resonances of base and collector chokes far apart, damping the chokes with resistors, using RC combinations for absorption of unwanted frequencies, using feedtrough capacitors for bypassing on the board, etc. It took some tweaking, but the amplifier ended up unconditionally stable.

The impedance matching network between the two transistors calls for such a low inductance, that it would be impractical to make it with actual wire. So I used a micro stripline etched on the PCB. Also, the power and SWR sensor at the output was made with micro striplines.

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http://ludens.cl/Electron/fmtx/fmtx.html
Thank you.

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