[TenTec] Corsair SWR goes high as power is increased

[Gary Follett]

Has anyone else seen this before?

He Corsair II operates perfectly into a dummy load, all bands.

The owner’s complaint was that the radio shows high SWR at high power, a condition I could not replicate into a dummy load on the bench.

However, when I tried a real antenna, things changed a LOT. I observed exactly what the owner saw, but only when the SWR was a LITTLE high, maybe 2:1.

These are photos from my spectrum analyzer, full power and about half power.

The radio is pretty clean with 14.6 MHz harmonic about 40 dB down.

It is clear that things get really bad as power goes up and the “SWR” readings are the result of all of this out-of-resonance signal, which is why the problem only shows up on a resonant load, not on a resistive load.

I did perform driver bias adjustment and final amplifier adjustment with no change in performance. Prior to adjustment, the bias for the final was quite high at 2+ amps, well over the 500 mA specified in the manual. I set it to the proper 500 mA. Still no improvement.

Gary Follett

W0DVN