SSPA 432 MHz - 1100W RF


For an amplifier solution with an output of just over 60dBm I chose Jim's proven W6PQL design. After my experience with his 23cm amplifier it was the obvious choice. Jim offers a kit with an ART700 transistor that puts out around 600W of power. So I ordered two pieces and decided to put them together. You can see what the whole build looks like in the pictures below. After testing in the final circuit and layout, the amplifier has around 21 dB of gain and puts out 1.1kW RF at 11W input power. Both amplifiers are mounted on a large heat sink which also serves as the base of the ALU box. There are two 48V fans on the side of the heatsink and one smaller fan on the lid to provide cooling for the interior. The inlet is a 90°hybrid from Pasternack and the outlet is a Kathrein with 7/16" connectors. For the inlet and outlet I milled small brackets out of copper, which also worked well in my 1296 MHz design. You can see the individual construction details below.

Block diagram of the amplifier. This is how I imagined to make it

And this is what the amplifier looks like. The massive heat sink that forms the base of the box made of aluminium profiles. Inside are two W6PQL modules and the necessary jewellery to connect all the parts of the amplifier.

This is a wiring diagram of the W6PQL modules. More details can be found on Jim's W6PQL website. Jim sells these modules as kits or as finished and revived modules.


I milled SMA connectors and coaxial cable holders from copper for screwing to the modules.


Fixing with Imbus M3 screws


SSPA in the dish

I connected the whole amplifier to a 50V/A power supply with a fast electronic fuse and set the idle current of the amplifier. Each module is set to 1A current. This is the current that flows through the transistor when the gate voltage is 2.1 V. Then I connected a DC 50V/40A regulating power supply. For the first test I used 0.5W excitation power. Everything behaved normally and with 1W excitation on the input, the output power was 100W RF. The amplification factor was therefore 20dB exactly as expected. Next I increased the excitation linearly up to 11W RF and measured an output power of 1100W RF. The circuits and the whole amplifier are working normally so I am looking forward to try it in a dish during some EME contest.


First test of SSPA