Topband: Coax Shield vs. Ground & elevated radials
bm at broadcast.se
Tue Jan 2 06:44:48 EST 2007
Thanks for the example, it is very good reading!
I agree it would be useful to measure the feed line current, but what I have
at hand is a Palstar ZM30 analyzer, a multimeter and a RF probe. I wonder if
there is a way I could use the probe and some construction with a coil to
detect the presence of feed line current?
Here are some more details of the antenna;
The total length of the vertical is 18 meter and the antenna is fed at
ground level. A top hat of three fifteen meter wires are attached at 15
meters height and slopes to the ground at a steep angle, about 40 degrees.
Two 1/4L elevated radials are raising up from the base of the antenna to
around 2 meters height. Both radials are run about 10 meters then bent 90
degrees (towards the same direction) and passes over rocky ground at height
between 1-3 meter. The whole system has been tuned by adjusting radial
length. Coax feed line is around 50 meter. The antenna measures around 16-17
ohms at resonance and is fed though an unun. The station is grounded with
one rod, but I expect the ground to be poor and not help much.
I will try the coax choke at the next opportunity to see if I notice any
73 de Björn /SM0MDG
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