1.3GHz 20W PA

My plan to be QRV on 23cms EME continues to move forward albeit at a rather different pace to what I’d originally envisaged. After a period of many weeks where little progress was made I’ve focussed my mind on getting a small 23cms PA going, possibly inspired by my recent visit to the Martlesham Microwave Round Table 🙂

My goal is to have somewhere in the region of 120W at the antenna from a SSPA. To overcome the inherent losses in a long coax cable run on 23cms the SSPA needs to be as close to the antenna system as possible. The SG-Lab TR1300 produces approximately 2.5W output so depending on where the transverter and PA are eventually situated another small SSPA is possibly going to be needed.

I was very fortunate to be offered a complete kit of parts for a ~20W PA that’s based on a Mitsubishi M57762 Power Amplifier module. I initially thought that I would combine this new PA with the TR1300 in one neat enclosure but decided it would be better to keep things modular so there was flexibility in what went where, and for ease of repair should things fail.

The following photos show the build stages of this small PA.

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Those of you that have a keen eye may have noticed that the original kit came complete with a two-part enclosure. But like the majority of my smaller projects this PA has ended up in my preferred aluminium die-cast box. 🙂

The construction centred mainly on metal-bashing, not the part I generally enjoy. Strangely though this project was different, I really enjoyed the drilling and tapping of the heatsink, something I’d not done for probably 30+ years! Maybe one day I will find some enjoyment in spray-painting and my projects will not have the natural aluminium look finish… 😉

So far the PA is working as expected, with an attenuator between the TR1300 and the input to of the PA both sit side-by-side in the shack and the PA produces 18 – 20W (JT65). The TX coax run to the EME antennas (2m & 23cms) has a loss of ~3.6dB at 23cms so should I choose to place this small PA at the antennas there should still be sufficient drive from the shack to produce ~18W output.

The next step is to tidy up the transverter, band pass filter and switching.

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