Crank-up towers and serious VHF/UHF feedlines don't really go together,
but, if that's what you've got available, it can be made to work.
I'm currently using a run of 1 5/8", a run of 7/8" and a run of 1/2" on a
75' crank up. They are all suspended off a 3/4" diameter solid steel rod
'coax loop hanger' that Tri-Ex sold along with their towers. This is well
over 100 lbs of feedline when the tower is fully cranked up - not an
insubstantial weight ! These lines feed 432, 222 and a 50 MHz beam. I
would have liked to run a pair of 1 5/8" and a single 7/8" line, but I
thought that was just too heavy.
I am able to manage the hardline 'bundle' when raising and lowering the
tower without help, but it's not something you can ignore. If I could find
a suitable three or four position relay with low loss, high isolation and
KW power handling, I would remove all but one run of 1 5/8" and use that,
without a doubt. Such relays exist, but I don't have one.
It all depends on how critical your requirements are. If you can get away
with all 1/2" feeds (or LMR-400 of 9913 or. . .), it would be the way to
go. Three or four 1/2 lines probably weight less than one run of 1 5/8".
But, if you try to use hardline, don't try to hang the lines in loops when
the tower is down - suspend it from the top and take the time to dress out
the line on the ground as the tower comes down. MAYBE FSJ-4 superflex can
be hung like RG-type coax, but I'd be cautious, even with that.
-W9RM
Keith J Morehouse
Managing Partner
Calmesa Partners G.P.
Olathe, CO
On Mon, Dec 9, 2019 at 11:02 AM N8GLS <n8gls@arrl.net> wrote:
> Hi Kim,
>
> If you can, go with separate feedlines. You will have less maintenance,
> fewer potential issues with the additional "devices" in the line,
> significantly more set-up/operating options, and, more hair if you ever
> have to troubleshoot any problems. The later alone is a significant
> advantage !! Of course, just my opinion.
>
> Hope to see you again at the 2020 Hamvention VHF dinner !!
>
> 73 de Brad, N8GLS
>
>
> > On Dec 8, 2019, at 7:49 PM, Kim <whensley11@comcast.net> wrote:
> >
> > Hello all!
> >
> > I'm looking for feedback, suggestions, and experiences.
> >
> > I have a 72-ft crank up tower that I want to populate with multi-band
> VHF/UHF antennas through 1296.
> >
> > My initial thought was to use one feedline (heliax) with relays to
> select the source and the corresponding antenna.
> >
> > In raising and lowering the antenna my intention was to walk the
> feedline out to avoid kinks and sharp bends.
> >
> > Another approach would be multiple feedlines.
> >
> > There would be only one antenna per band for terrestrial work.
> >
> > Thank you for your time and thoughts.
> >
> > 73, Kim - WG8S
> >
> > _______________________________________________
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