Hi again,
At last, all four ravine and distance spanning ropes are in place.
Over 500 feet in at least three directions seems possible, somewhat
shorter (maybe 480 feet) in the leg running most closely to the West.
Not long now until we start to pull wire across, and thus a couple
of questions.
1. Had been planning to use 300 ohm windowed twin lead as the radiating
element. But, rcv'd a few cautions about excessive loss because of
the two #18 conductors in the line. Turns out, using K6STI AO program,
that sure enough, efficiency runs between 81 and 85% just from conductor
loss only in several hundred foot runs. Going to The Wireman's
insulated #13 with "Toughcoat" insulation, the efficiency rises
up into the low 90% area. So now have 2400 feet of that on order.
Now the first question: Is there any value in strapping both of
these conductors together, in parallel? Together they would about
be equal to the same radiating area per unit length as #12 conductor
alone, which wasn't available. I would just tie them together with
a nylon tie wrap every 10 feet or so. This would also increase the
weight, and perhaps up the wind resistance a bit. Is it worth doing,
or must I figure out how to sell off four spools of 300 ohm line, 600
feet on each spool?? This all got inspired by chit-chat on here some
weeks ago about loss in very long wire antennas, so I looked into it.
Of course, all three conductors will be tied together at both ends
if they are strung together.
2. Question two concerns static build up on very long wire antennas.
Lightening is just about a non-problem out here; last real "bolt"
lightening display here on Kauai was nearly three October's ago, so
it can happen. More common, yearly, is some cloud to cloud type
display and thunder. Usually never see anything except the bright
flash of light from the clouds, followed many seconds later by the
sound of thunder.
But my real question is rain and wind static charge build up. Will be using
insulated wire(s) no matter which way we go when the wire is pulled into
place. Rcv'd the following e-mail which really stimulated this post:
"Just wonder if you have considered the static build up that can occur
from wind or precipitation on a wire that is 300+ ft long. Your
YAESU FT-1000D solid state front end could be damaged from a static
discharge. The article(Colvin's) is based on 1956 tube technology that
was a lot more tolerant of this type of problem. Maybe a letter
to tower talk for any input. One article I read recommends a
2.5 mh choke on each feeder to ground to drain off static electricity.
Let me know how you make out????. I am installing an extended
ZEPP this weekend for forty mtrs with a length of 86.5 ft per
leg. Joe, K9DMV"
The rig will be "isolated" DC wise from the antenna system, as will
be using the E.F.Johnson KW Matchbox tuner to couple to the system.
The 50 ohm rig output is inductively coupled in this box using a
huge primary coil at the center of a band switch tapped,
longer secondary coil which runs inside the input primary coil.
The Matchbox obtains its
impedance matching by means of the proper ratio of capacitors in
series across the output parallel resonant tank circuit. C1 is the
principal secondary coil resonating capacitor, however, the dual
differential cap in series will also contribute, but C2's principal
job seems to be to provide the proper division of impedance to match'
the transmission line and compensating for any reactance present.
The two wires of the balanced transmission line are connected to
the center sections of the C2 differential capacitor, so are dc
isolated from the secondary tank coil, and, thus do not "short"
out any static charge on the line.
Appreciate all the input you of this great reflector have contributed
already. Any thought on these two points before we start pulling
wires across the ravine?
73, Jim, KH7M
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