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I performed an interesting shielded loop experiment today with a snap-on
ferrite rfi-choke: 1) When the choke is placed anywhere on the coax feedline the choke has no affect whatsoever. 2) When the choke is snapped anywhere around the loop-element coax, it really attenuates the loop signal, and also detunes it. I had to readjust my tuner's capacitor quite a bit. It also seemed to flatten out the nice sharp Q. It did not affect the directivity however. Placement of the choke anywhere on the loop element seemed to produce the same amount of attenuation - from right over the gap to anywhere else on the loop. Unless I misunderstand how ferrite-chokes work, this does seem to physically point out that the shield is the actual antenna. (This is what I've been told all along here.) Nobody in their right mind would place an RFI choke on their transmission line in an effort to reduce common-mode radiation if it also severely attenuated the wanted signal right? Am I on the right track? The correct theory is nice to know, but it is also great to see it proven physically.... 73 Brian |