Hi Boys,
Anyone of you actually used coax in this configuration? I have. Fed a
40m loop, tri-band Quad, mono-band beam and 160m dipole.
The loops were fed with the shields tied together at the antenna but not
connected. At the tuner side the shields were tied together and
connected to ground.
For feeding the beam, the driven element was a split dipole with hair
pin match. The connection at the tuner end was the same as with the
loops. The connection at the driven element was different. The center
conductors connected to one each of the dipole elements, as you would
expect. The shields were tied together and grounded to the boom. The
hair-pin match was adjusted to match the 104 +/- ohm coax line impedance.
One could hear the difference in common mode/static noise pick-up
between a single coax and the shielded pair line (the shielded pair was
very quiet).
For the 160m dipole the antenna side was the same as the 40m loop with
the exception that I added a pair of 2.5mh chokes that went from each
side of the dipole element to the bonded shields. The antenna was
strung between three 100' white oak trees and prior to going to twin
coax I had open wire line. However, the static charge buil- up on those
wires during lightning storms would melt the feed-line right off dipole.
Some mornings I wake-up and see little white insulators scattered all
over the back yard. Problem solved with twin coax and chokes installed.
So, don't know what the book says or EZ, etc. just know that is the way
it worked for me.
Have Fun,
dave
wa3gin
k1ttt@arrl.net wrote:
>>The dialectric has very little effect if you do not have the shield hooked
>>up at both ends. Coax is coax only if you use the shield.
>>
>>
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