Hi
It would make sense to confirm the A3 as the cause of interaction first, no?
Thinking you could simply lower the A3s and then determine what effect it has
on your VHF yagi.
Also, how do you know the resonant frequency of the VHF beam? Are there
measurement issues at play? If you're measuring it at the far end of the
feedline, is the feedline introducing some error?
Your project isn't a small one, so it would be nice to know it's going to help
before going to that effort.
73,
Kelly
ve4xt
Sent from my iPhone
On Apr 27, 2013, at 11:35, "Robert M0RCX" <m6bfd@yahoo.com> wrote:
> 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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