How does a radiating feedline cause TVI? That depends on the individual
case, but...
In my case a radiating feedline about 20 feet from the local CATV system's
cable put enough energy into the CATV system to knock out the Playboy channel
over most of our block. The local bunny fanciers were outraged, as were the
late night porn movie fanciers.
I had coax running almost in contact with the CATV cable with no interference
to any channel - but any attempt to use the open wire line resulted in nasty
telephone calls. While the SWR was well within 2:1 (a folded dipole radiator
and 450 ohm wire) and was actually less at the band edges, efforts to reduce
feedline radiation proved fruitless.
After some effort to get the CATV system to either replace their defective
cable, or at least step up their signal enough to override the leakage, I
gave it up. The same antenna with a choke balun followed by a 4:1 balun at
the feedpoint is completely TVI free.
73 Pete Allen AC5E
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