500 mW RF amplifier for 170 MHz design

Electrical Engineering Asked by betex on January 6, 2022

For a new project I need to build an RF amplifier for continuous-wave with about 500 mW (27dBm) output at 170 MHz.

It doesn’t need to transport data, it is only for measuring purpose.

The input comes from a signal generator, that can go up to about 15 dBm output, so the amplification needed is about 12 dB. The circuit should run with 5 V supply voltage.

The output of the RF amplifier is directly connected to an antenna, that is matched to 50 Ohm at 170 MHz.

A simple solution without big matching effort would be preferred, as I don’t have much RF measuring equipment, only a cheap chinese network analyzer (NanoVNA).

So far I tried some ADL5535, but always when the output comes up to 500mW (14Vpp) they got killed.

The same experience I had with a BFQ790. It was drawing about 500mA, when the output was OK, but then also died.
Heat dissipation should be no problem, as I’m using the PCB (with heat sink compound) of a former destroyed amplifier module for my experiments, see pictureenter image description here

I’d really appreciate some help, how to design a simple circuit, that is more robust against mismatching of the antenna. I know some theoretical basics about T or Pi-Networks, but I’d rather need some practical support.

Maybe someone has an example circuit (with components, that sill are active and available).

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