re: antenna gain


From: William R Colbert (af852@rgfn.epcc.Edu)
Date: Wed Jun 25 1997 - 21:48:25 EDT

I think the reason for using the disapation resistance at the end
of a long wire, V-beam or Rhombic is not to disapate power but to
set the directivity. Not sure if the lossy ground will work or not.
I have used a similar ground but also used a terminating resistor
in the series with the ground. One thing that does work is nickle
plated steel - had a little transmitter at work once that had
a number of rhombics tied to it and the feeder was 00 phosphor-bronze
spaced at 12 inches and the terminating system was the nickle plated
steel, measured out in 10's of feet, set up just like a balanced feeder
and run back on short posts to a ground rod. The wire
disapation system measured out to 800 ohms, made from 02 nickle plated
steel. Oh the transmitter ran 6 3cx2500a's driven by a pair of
4-400's 3-28 Mhz. For qrp levels a small resistor will work
fine for the setting of the directivity. Mechanically tho, it would
need some sort of support. My last big antenna system with V-beams
consisted of a rosette of 5 sloping Vee beams and they had a terminating
resistor on each leg to ground - 400 ohm each for a total of 800 ohms,
and the balun at the feed point was 12:1, which was pretty close to
what it should be. Worked very well and instant directional change
at the push of a button. 505 feet per leg.

Directional antennas on 80, 40, 30 are very
desirable especially here on the Mexican border. Even on 160 if
I worked that band. At present my antenna is a pair of Cushcraft AP8A
verticals with a phasing unit at the operating position, capable of
unidirectional operation NE/SW and bi-directional NW/SE. It is
very worth while to null the direction that one is not wanting to
listen to or transmit to. also known as low density operation, or
spectrum conservation. The ideal way to use the unit is once a cq
call is made, the antenna is switched between all positions or placed
in the bidirectional mode to listen for calls.
My dos pesetas worth.
72/73 Ray

Ray Colbert, W5XE
OOTC 3618, SOWP 1064M
El Paso, Tx (Far West Texas)

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