23CM 600W Power amplifier

Carsten Groen's (OZ9AAR) personal place

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23CM 600 W Power amplifer

As I'm waiting for the mechanics to be produced for my coming 4.8 meter dish for 23cm EME, I started looking into building a suitable power amplifier for the system. 


Again to "get the most" out of the amplifier and at the same time, save some space in the lab/shack, I decided from the beginning that the PA should be mounted near/at the dish. This will allow me to use the shortest possible coax between the PA and the feedhorn, and also remove the need for flexible "around the rotor" high power/low loss cable to be used. The PA will be remotely controlled and monitored using my REPAM and Dual RF Head modules.

I used the same principle in my 500W 70 cm power amplifier used in my current 70cm EME system.


  

So far, the system consists of the following sub modules, some designed by myself, and some bought:


  1. Cooling system with two fans. I designed a "generic" system that can be used in other PA systems.
  2. Overcurrent detection and on/off switch. Described and documented here also.
  3. Dual RF Head (logarithmic amplifier) that samples the fwd/ref signals from a directional coupler.
  4. Remote PA Monitor (REPAM), allows control and data collection/security of a remote PA.
  5. W6PQL 600W module (I selected the "kit form" of the modules, assemble yourself)
  6. Power supply from RECOM RACM1200-48SAV/ENC: Datasheet for power supply
  7. Various stuff for mounting, a relay for remote power/on off, a 12VDC PSU (for bias etc)



PA/Heatsink/Fan assembly

The completed assembly, PA module in milled aluminium box and heatsink with fans will look like this.

This is the exact same heatsink/fan assembly as I use in my 500W 70cm PA module.

Below is a dual module solution, also shown is my 23cm high power 90 deg. hybrid.

Enclosing box

I decided to design a milled aluminium "box" that would contain the PA module, connectors for in- and output and a few feedthrough capacitors. Jim (W6PQL) suggested that it was a good idea to cool the output components on the PA module as they can get warm at full output. I designed the lid for the milled aluminium box so a 60x60 mm 12V fan could be mounted.

I also designed a copper heat spreader for the module and had that manufactured at the same time as the milled box and lid. Shown on the screenshots below are also two small brass strips that will be used to solder the coax cables to, these will then be secured to the PCB/heat spreader with two M3 screws.

The extra M3 screw in the "LDMOS trench" is for a temperature sensor (1-wire DS18B20 sensor that connects to the REPAM module).


The data for the box will be available for download here once I have verified everything. The copper heat spreader design will also be available for download.

More info to come...