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Now that my remoted AT-600 Pro II seems stable, I was surprised when the SWR rose while in an extended set of FT-8 QSOs running 100 watts.? I set the radio to FM and went key down.? This was putting out 100 watts into a tuner supposedly rated for 600 watts.? After a short time, the SWR started rising.? I doubt the heating is in the ferrite choke balun on the RG-8X between the tuner and the antenna.? The problem is worse as I go down in frequency, and is negligible on 20 meters.? It is probably manageable on 18, but worse on 30 and serious on 40 and 80.

I presume this is due to the Q of the coils in the tuner.? The options I have to feed the antenna, a 20' flagpole OCF dipole, are direct with a choke balun, a 1:1 ferrite core balun, and a 4:1 ferrite core balun.? I'm guessing that as I go down in frequency the antenna is becoming more capacitive and thus requiring more inductive loading.? If I put the 4:1 balun in that should cut the reactive component by a factor of 4, right?? That might solve my problem, at least at 100 watts.

Looking for suggestions....

Thanks,
Al K5TAN

I have done some more investigating.? The problem only occurs on 10 meters,? The model I constructed for the antenna on Expert MININEC shows that the impedance presented to the tuner should be around 284-j24.? This impedance is predominantly resistive.? I intend to confirm (or deny) this with my NanoVNA.? Should the AT-600 ProII have difficulty feeding a high resistive impedance?

I forgot some history that might be confusing readers.? I found a bend in the RG-8X that was heating on the lower bands, replaced the coax and improved the cable routing.? The problem no longer exists on any band other than 10 meters.