Been running the BEKO HLV-523 500W amplifier for 23cm EME but experiencing thermal shutdowns during 60-second Q65 transmissions above 200W output. Initially had a Gemini 23 PA that would temperature trip during Q65 bursts, had to back it down to 120W. The HLV-523 seemed like the solution but now having similar issues. Discovered arcing at the output cable interface - turns out the semi-flex coax was only 0.114" rated under 300W for a 500W amplifier! Replaced with 0.25" coax and solved the problem. Anyone else run into power handling issues with microwave EME amplifiers during long digital transmissions?

Common issue with higher power microwave PAs - the RF power density is so high that any weak points show up quickly. Using undersized coax for the power rating is unfortunately common. Also check your SWR under full power - even 1.3:1 can cause significant heating at 400W+. Many ops add forced-air cooling and SWR protection circuits for Q65 operations.

Good catch on the coax issue! For 23cm EME, we typically use Q65-30B, Q65-60C, then Q65-120D in order of increasing sensitivity. Haven't used Q65-120D due to PA limitations myself. The longer transmission periods really stress the thermal design. Consider adding a duty cycle monitor - some ops limit to 50% for thermal management on these high-power microwave amplifiers.

Q65-30 sec periods really increase the number of QSOs compared to longer sequences. Shorter periods mean less thermal stress on your PA. The trade-off is slightly reduced sensitivity, but if you're running 300-400W you probably have enough margin. Also helps reduce Doppler issues and keeps the QSO rate up during good conditions.