[TowerTalk] Heliax and crankup towers

[Al, N6TA]

Ever notice those mobile TV vans that do remotes from the field and
microwave the signal back to the station?  They get their signals from their
little microwave transmitters up their telescoping mast to their directional
antenna using a corrugated feedline similar to Heliax and other similar low
loss cables.  The feedline is coiled up around the mast but the cable is
never really bent much.  In this kind of application, it is quite durable.
Doing the same to your telescoping tower might work out.
Al

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com]On Behalf Of Gary Mitchelson -
N3JPU
Sent: Sunday, May 02, 2004 08:54
To: towertalk at contesting.com
Subject: [TowerTalk] Heliax and crankup towers


I looked through the archives but did not find conclusive info on this
topic.

I am going to upgrade my 50 and 144Mhz antennas and will also put new coax
in place. Currently I am using 9096 Extraflex which is a air dielectric
(similar to 9913F7, with 2 shields) and has a loss of .9dB/100'@50Mhz and
1.5dB/100'@144Mhz. The runs from radio to antennas is about 75' on each
band.

My tower is a 2 section crank-up 38' with a fold over base. Probably fully
fold it over once or twice a year, and crank it down about 4 times a year.

I was considering LMR-600UF coax as 1) it has lower loss (but on 50Mhz I
would only save about .2dB and on 144Mhz about .3dB) BUT the power handling
goes up to a more comfortable area (LMR-400UF has a bit more loss than the
9096 I am currently using).

The cost of LMR-600UF is a bit high, so another alternative is some
attractive pricing on Andrews LDF4-50A Heliax (less than 1/2 the price of
600UF at a few sources). There are also some good prices on the FSJ4-50B
superflex Heliax which almost is as good as the 600UF loss, but way down
from LDF4-50A.

However with either I would need to put rotor loops in where the 600UF would
not need any. So that means 4 extra N connectors inserted in each run. So
that adds to the loss a little bit and to the cost bringing the Heliax
solution up close to the LMR-600UF solution.

How would either version of the Heliax stand up to the occasional action of
cranking the tower down? I know that the spec on bending either heliax is 50
but not sure how that compares to looping 20' or so as the tower nests. My
concern is the life expectancy of the Heliax vs LMR-600UF.

Also, anyone using LMR-600UF? And how is it holding up? The jacket is not as
good as the regular LMR-600 from what I see.

Gary Mitchelson
N3JPU Montgomery Co. MD  FM19
http://www.mitchelson.org/

USAF MARS and SHARES station AFA1PU
Maryland/DC USAF MARS SMD AFF1MD
USAF MARS Region 1 MTS AFF1M
MD/DC MARS homepage http://www.mdmars.org

_______________________________________________

See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.

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