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Author Topic: Coax & Antenna mast choices  (Read 812 times)
KC8FPU
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Posts: 4




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« on: March 07, 2003, 01:42:20 PM »

Putting up new tower with Cushcraft antennas 6el 6m beam, 26B2 2m beam, 719B2 stacked pair 440 beam, and a Comet GP-15 tri-band. The 2m & 440 beams are on a crossbar mounted on the main mast with the 6m beam and GP-15.

How do I calc mast sizes? What should I use, steel, alum, fiberglass, etc.

Which coax would be better CXP1318FX or LMR-400-UF?
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WB2WIK
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Posts: 20559




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« Reply #1 on: March 07, 2003, 07:03:19 PM »

You don't need to calculate mast sizes.  Stacking distance (separation between antennas) is specified by Cushcraft, and the mast diameter to use pretty much is, too, by the size of the U-bolts and backing plates provided.  If those are 1.75", then that's the size mast to use.  If they are 2.00", then that's the size.

What you didn't say, however, is whether the 2m and 70cm beams will be horizontally or vertically polarized.  

If horizontally polarized, you have no choice but to make the crossbar (horizontal boom supporting those sets of antennas) out of a non-conductor like fibreglas, since anything conductive won't work.  I don't think Cushcraft supplies fibreglas masts, but M-squared (M2) does.  They are not for the faint of heart, as they are quite expensive, but you've no other choice if this is what you're doing.

If the 2m and 70cm antennas are vertically polarized, however, then the crossbar can be aluminum or steel.  1/8" (.125") wall thickness high carbon steel is fine, or 1/4" (.250") wall thickness extruded aluminum hollowbar 6061T6 alloy is fine, too.  They both offer about the same strength, with aluminum being lighter but steel being less expensive.

Good luck with the installation!

WB2WIK/6
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KD5VHF
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Posts: 84




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« Reply #2 on: March 08, 2003, 09:16:26 AM »

Quote: "Which coax would be better CXP1318FX or LMR-400-UF? " I prefer the Davis Bury-Flex http://www.davisrf.com/ham1/coax.htm  
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K9KJM
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Posts: 2416




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« Reply #3 on: March 19, 2003, 01:06:46 AM »

LMR400 series coax is the ONLY choice for VHF/UHF
use. (Unless you go even better, to LMR600 or Heliax) There are several versions, Solid center conductor, Stranded center conductor "Ultra flex" and
maybe a few more.
If the coax will be going around a rotor that will see
lots of use, the "Ultra flex" would be the version to
get. Otherwise, The plain LMR400 is a little cheaper.
Take your time installing connectors and do a good job.
AVOID Belden 9913 coax. Lots of horror stories about
it that I have seen from first hand experience!
Belden has made lots of great cable over the years
(And still does) But the first three or four versions of 9913 were NOT good......)
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