On Friday, November 15, 2013 3:17:48 PM UTC-6, David Platt wrote:


That's pretty much the conclusion that I had stumbled my way to, after

thinking about the question over the past few days.



It's possible that the length of the feedline might be an issue. The

impedance seen "looking down" the outside of the feedline coax could

vary a lot depending on whether it happened to be closer to an odd or

even number of electrical quarter-wavelengths. This could

significantly affect the antenna system's overall pattern (a low Z

along the braid would result in greater current flow and more RF

radiation/pickup from the feedline).



Adding some ferrites to the end of the feedline, just below the point

of connection to the (noisy) dipole, might bring this antenna "to par"

with the others.

He said that the beads on the line helped, which pretty much
confirms the problem is common mode. I bet if he switched from
the simple gamma match to say a T match, or whatever that is more
balanced, and then added beads to the line about 1/4 wave down
from the feed, that would probably help a good bit.
The gamma match usually works OK, and I've used it quite a bit.
But it's not the best matching scheme out there.