Cecil Moore wrote in message ...
Mark Keith wrote:
"Tom Coates" wrote in message ...
The writeup says the terminating resistors make it non-resonant. I wonder
how they affect efficiency.

Seems to me it's already non resonant except on certain frequencies
where it's multiples of a 1/2 wave. But you do have reactance on most
frequencies. The resisters absorb rf that travels along the wire to
the resister. The rf traveling to the rig in the other direction, is
absorbed by that load. So there are no standing waves. Basically, all
the resisters do is make the antenna fairly unidirectional. About the
same deal as a terminated rhombic. You have a good f/b ratio. But
overall total efficiency is appx cut in half, being the waves to the
resister are absorbed. I think this is correct anyway...:/ MK

What Tom probably means is that the resistors turn the antenna into a
traveling wave antenna where the feedpoint impedance is a few hundred
ohms mostly resistive over a relatively wide range of frequencies. It
is somewhat like that infinite feedline that we sometimes talk about.

I guess so. But I think it already qualifies as a traveling wave
antenna on the bands where the wires are actually long enough. My
moment of indecision really came trying to decide if the reduction of
the wave towards the resister qualified as a reduction of efficiency,
or would be a directive loss, IE: like the backside of a yagi. I guess
from reading Roy's post, it does qualify as a reduction of efficiency.
I hope I read that right anyway...But like he says, if you are working
a station in the opposite direction of the resisters, "IE: desired
direction" the loss of efficiency doesn't matter. That lobe *should*
stay appx the same. You are only knocking down the unwanted wave to
the rear. So the gain to the desired station you are pointing to
should be about the same as without the resisters. But the s/n ratio
should improve as you lose the crud and extra noise off the back. Am I
correct here? If not, feel free to jump in... MK