[TowerTalk] Bead chokes on feedlines; K3LR array
Pete Smith
n4zr at contesting.com
Mon Nov 8 14:42:25 EST 2004
Tom's excellent message this weekend on use of current mode chokes on a
feedline caused me to reflect on(no pun intended) my K3LR-type 80-meter
array. It uses four dipoles arranged in a lazy-vee configuration. Because
of space limitations, the dipoles' upper legs are straight, while the lower
halves describe roughly a quarter circle in making their way back to the
tower at about the 7-foot level. The feedlines for each dipole come back
to the tower at roughly the 25-foot level, thence down to the switchbox
near ground level.
When I built this array, I put 50-bead chokes at each feedpoint, thinking
that I would help suppress common mode currenst and thereby avoid any
destructive interaction with the antenna pattern. Now, however, Tom makes
me wonder if this is useful at all, given that the feedlines are in the
very near field of the dipoles anyway. Would I be just as well off to
eliminate the chokes altogether, or do they serve a useful purpose,
assuming they are of the right material and have enough inductance to do
the job?
The antenna has been up and working pretty well for 6 years. I ask at this
point because 2 of the 4 dipoles quit working at the start of Sweepstakes,
and I'm thinking it is time to replace the feedlines before winter sets in
further.
73, Pete N4ZR
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