Topband: FEEDING AN END-FED LONGWIRE

[Tom Rauch]

Of course Jose and others are correct in saying these antennas radiate and
can work quite well. The only important point I wanted to make was the two
wire feeder common mode current (which makes the feeder radiate) varies huge
amounts with the type of matching system and lengths chosen. If the antenna
flattop is not exactly 1/2 wl long or low-order exact multiples of 1/2wl,
common mode current increases dramatically. The same is true for some common
mode impedances of antenna tuners.

That feedline going up to the antenna must look like a very low common mode
impedance compared to the antenna, so the antenna and feedline are greatly
mismatched  for common mode impedances (the antenna being as high as
possible, the feeder as low as possible).

It really a very complicated interaction between the type of tuner and
length of feedline and antenna. One article by a west coast amateur several
years ago "proved" the feeder radiation was nearly zero, but the author used
a model with a "perfect" floating source and exact length feedline and
antenna. This would be nothing like the real world. The article was more a
demonstration of how software models can build things that can't actually be
constructed in the real imperfect world. But imperfect does not mean it
won't do what we need.

73 Tom