I tried to follow recommendation from Chavdar's app note in regards to feed cable location (for vertical dual loop configuration). Here is a picture:
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Although in the notes Chavdar recommends 1-2m offset for the cable behind the loop's plane. I only have ~60-70cm (2ft) due to some space restrictions.
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I noticed that in Dipole mode I see about 5dB drop in AM BC station images in the lower 80m band. That's due to CM issues in dipole mode. Not sure if that was worth the hassle as loop mode is still superior in my noisy environment (semi-urban location).
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I also noticed that top loop (Loop A) usually provides better s/n ratio compared to lower loop (loop B) and cross-parallel connection of both loops. I see that on most HF bands. Sometimes LoopA=A+B but usually I just use loopA. I was wondering if that's due to the cable that was hanging right across the lower loop. New cable placement improved things a bit but I still see LoopA normally being better or equal to A+B configuration. LoopB is still normally worse than other two configs (A, or A+B).
Next I may try to put more clip on ferrites along the portion of the cable that hangs below LoopB. Maybe mix31 and mix75 clip-ons combined on the length of 1-3m up to the point where cable comes to the wall. I already have a stack of two FT240-31 with ~6 turns of CAT before cable leaves the amplifier box and a stack of three FT240-31 with 6 turns before it enters control switch box. That actually helped a lot but I wanted to improve things even more.
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I wonder if Loop A is better simply because it's higher in the air and further away from my "shack" that's 2-3m away from the antenna physically.
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Also may try to place Yaesu GS-050 mast bearing a bit lower. Right now it sits right below the lower loop. Wonder if that can create any un-balance issues.
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Regards,
Simon
KM6MUL
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