Hello I am new to the forum and thank you for your acceptance into the group.
There have been many discussions on wind loading to mast supported antennas but
I was wondering if anyone has calculated forces applied to stub masts and how
they vary with extra length.
We have an hf A3S with 40m add on at 60 foot max elevation. Immediately above
it we have a 6 element dual band VHF beam for 70 and 50mhz.
We wish to raise our stub to increase the distance between the two and help
reduce SWR on 70mhz which is currently resonant at approx 70.600 and as such is
out of band Ideally for us resonance should be about 70.300 ish.
We feel the hf beam is almost the cause of this.
The setup tolerances of the antenna are very tight and spot on for manufacturer
recommendations.
We use a 2 inch diameter stub of approximately 6 foot. 2 foot approx are in
rotator cage and there is three feet between beams.
We would like to extend by another 10 feet giving us 14 foot of available stub.
Our rotator can cope with this but when tower is over we need to wind out to
facilitate ground working without catching trees etc This extra length
applies more forces when cranking the tower back to vertical position.
We feel out stainless winch cable should support it but this subject has opened
a whole network of interesting questions and the theories and was wondering if
any of you guys has such a formula or has any experience on such matters.
In particular
A. Strain to cabling
B. additional force added by increasing stub length
Any experience is most welcome
Robert Rawson
M0RCX
North Wakefield Radio Club
www.g4nok.org
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