In article , Richard Fry wrote:

Could somebody please explain why feedline SWR should produce any more
general TVI in the neighborhood than if the match is perfect?

My guess is that this belief is true in some cases... specifically the
following:

- You have a dipole, or other balanced antenna
- You're feeding it with coax
- The dipole has a feedpoint impedance which is high (resistive
and/or reactive) at the frequency of interest
- You don't have a balun at the feedpoint, or your balun has only a
modest amount of choking reactance
- Your coax is somewhere near a half-wavelength long (or a multiple
thereof) from the antenna to the point at which its first ground
occurs.

In this situation, you're likely to have a lot of RF on the outside of
the coax, as its braid will present a path for the ground-side current
which is significantly less than that of the antenna. You could end
up with "RF in the shack" problems, or the various other problems
which can result from having high levels of RF flowing near other
consumer-electronics devices.

If your feedline happens to be parallel to a cable-TV line, its
radiation may tend to induce a significant RF current on the outside
of the cable-TV coax, and might bleed to the inside. This could
result in fundamental-overload problems in the TV or distribution
amplifier.

If your feedline runs near a metal gutter or downspout, or near a
stucco wall with chicken-wire mesh in it, it might induce strong
enough RF currents to cause rectification noise in the joints, and the
generation of undesired harmonics of your transmit frequency which
might fall into the TV frequency band. Similar generation of
harmonics can occur, I gather, if you push a ferrite-core balun too
hard, and saturate the ferrite.

If I recall correctly, 6-meter operation is notorious for causing RFI
due to both fundamental overload (Channel 2 is often affected due to
its proximity to the 6-meter band) and to second-harmonic spurs
falling in the FM band.

If you've got RF coming back down into the shack, you might have some
of the RF-ground current getting into your household AC power ground,
and bleeding into the TV sets via their line cords.

All of these are things which can occur with any antenna, of course...
they're just exaggerated (to whatever extent) by RF-on-the-coax due to
the RF's greater proximity to the affected TVs.

In all of these cases, I'd expect problems to be more apparent for
nearby TV sets (same building) than those far away. In urban areas,
with people living in apartments or condos, the "neighborhood" can
consist of quite a few people living in individual households within
100 feet of the transmitter and antenna.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
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