Looks like massive amount of FT240-31 cores with as many turns as possible do really solve this problem. I used a stack of 2xFT240-31 on CAT cable with about 8 turns right next to antenna and 3xFT20-31 stack next to control board. Even have one single core in the middle of my CAT cable (although I'm not sure if that's FT240-31 or FT240-43). Also some on 50 Ohm coax that goes to my receiver (next to control board) and a core on control cable (next to control board) that goes to mode switches/power. I have control board in a separate box sitting outside of my "shack", so I only have 50Ohm and "control lines" coming into the shack.
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So, my initial thoughts about Hi-Z amp being power overloaded by local AM stations were wrong. And thinking more about that I see where I was wrong initially: if Hi-Z amp was overloaded (in saturation) it should produce quite a high level at the output that should overload my SDRPlay but that wasn't happening!
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I must say that almost anywhere Loop low-Z amp still outperforms "Dipole" Hi-Z amp. I haven't tried 10m band as I see almost zero activity there but 80m - 20m Loop mode works just better (better SNR) in most cases. But then again I live in Silicone Valley noisy environment.
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Regards,
Simon
KM6MUL
