Thanks for the responses.

Put differently, I guess the purpose of the entire station is to radiate
and intercept radiated waves containing information. I was trying to
explore the benefits and consequences of preventing transmission line
radiation as they relate to this more global purpose.

While it is clear that maintaining balance in the line will prevent
radiation from the line, some (maybe all) of the radiation prevented
might have contributed to the global purpose of the station. For
example, radiation from common-mode currents in a vertical transmission
line could produce beneficial low-angle, omnidirectional radiation, as
has been pointed out often on the group.

It would seem that for the common-mode transmission line currents the
antenna system would look like a top-loaded vertical, ignoring the
balanced line currents and their interaction with the horizontal portion
of the antenna.

The efficiency of the vertically polarized radiation from the line would
depend heavily on the station's RF ground system. But basically we would
have (for the common-mode currents) a conventional vertical antenna with
all its attendant plusses and minuses.

To the extent the AC grounding conductor in the house presents a lower
impedance than the station's RF grounding system, we would expect to see
displacement currents in the AC system, just as with an "ordinary"
vertical using a poor RF ground.

Coupling to the telephone wires also would seem to be a consequence of a
vertical radiator with a poor RF ground, rather than a consequence of
transmission line imbalance (which I understand is the cause of the
radiation in the first place).

So here is my main question: do we object to the vertical radiation per
se (i.e., if we wanted vertically polarized radiation, we would have put
up a vertical in the first place), or is radiation from an unbalanced
line somehow more insidious in that it causes other problems that
"ordinary" verticals do not cause? In other words, why do we really care
about imbalance?

Reg has called attention to another of my shortcomings: I have no idea
how the common-mode line currents that enter a link in the tuner are
seen and "processed" by the tuner. It would seem that the link appears
as one plate of a capacitor for those currents.

Thanks again for everyone's patience.

Chuck, NT3G






Cecil Moore wrote:
chuck wrote:

If there are no obvious common mode currents causing problems in the
shack, then of what consequence would an imbalance be, other than to
modify the radiation pattern, perhaps even beneficially?


The purpose of the antenna is to radiate. The purpose
of the transmission line is to transfer the energy from
the transmitter to the antenna with as little loss as
feasible. How much an antenna system is allowed to
deviate from its purpose is up to the individual. When
I was in high school, I didn't much care about the purpose
of an antenna system and burned a hole in my lip.