[TowerTalk] Heliax, Lmr, Bury-Flex Info & Conduit Pull Thrus
DavisRFinc@aol.com
DavisRFinc@aol.com
Tue, 14 Mar 2000 00:54:04 EST
Hi Tom,
Andrews spec's this cable at a 5" bend radius. If the "sweep" you mention
is good for this 5", which I doubt if it was not "overly" constructed with
sweep joints, you will be exceeding that 5" min. spec which is not good.
One problem with Heliax is that it requires greater bend radius than other
cables of equal performance (some others are not as good attenuation at
microwave though).
The plus side of Heliax is its mechanical strength particularly as related to
its tensile and elongation ratings. This lends itself well to hoisting up
large commercial towers.
For ham use below 440 MHz, I have to be frank and say that the extra
mechanical ruggedness of Heliax is not necessary and the attenuation
improvement vs. LMR or "BURY-FLEX" Tm is minimal at best (unless we're talkin
very low power at above 230- MHz). The premium you pay for the Andrew name
and the extra mechanicals (not to mention connector expense) is considerable.
You also deal with higher bend radius as noted.
The 4 bends you mention are no problem if IAW the 5" spec.
Direct burial is not a problem, another plus of the mechanical construction.
Not only is the PE (polyethylene) outer jacket a must, the shield below it is
a copper conduit, thus "vapor transfer" of moisture is inhibited. Also,
this conduit type construction lends itself to protection of the inner
dielectric and center conductor ref. possible vulnerability to an errant
sharp spade shovel, etc. as your wife or significant other is in the "red
zone" trying to plant flowers or whatever.
So, without further data, which I'd be glad to go over with you in a direct
email, I'd say, "If no 5" min radius, direct bury it. If you have a muscle
bound "significant other" who likes digging holes, put it in a conduit and
find her a field she's safe in.
I sell all three of the above mentioned cables and connectors at the lowest
pricing I'm aware of so it doesn't matter to me. However, I will ask any
customer what the application is and advise as noted above. That's only
ethical.
By the way, the idea of vacuum suction of a string thru PVC is a good one.
Just don't do what a guy did: Make sure if you use light weight yarn, that
the other end isn't attached to a SIP (sweater in progress). Turned that
sweater into a neat "tank top" in 2 seconds. Cheers, Steve Davis, K1PEK
DAVIS RF Co.
note: comparison to lmr 600, .590" OD, not lmr500, .500". price comparison:
4-50A: 1.79/ft vs. $1.13 dir. bury lmr600db (or .98/ft std.) LDF 4 atten. @
450 MHz=.21 dB nom. improvement; @ 30 MHz=.16 dB (100')
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DAVIS RF Co., commercial wire and cable, custom cable design. Discounts to
hams. Heliax, LMR, RFS, Belden, BURY-FLEX Tm. Various aerial wiring; wire
aerial parts; transmission lines, insulators, baluns, RF connectors and
Dacron rope. www.davisRF.com . 1-800-328-4773, (For all RF hardline related
items, please ask for Steve Davis) Thank you!
"The Triad": Davis RF Co.; Orion Wire Corp.; and The Wire Man, Inc.:
Variegated expertise; resources and buying power yielding numerous quality
products at highly competitive pricing.
~ Davis RF Co., Div. of Davis Associates Wire and Cable, LLC:
Distribution to numerous industries, Price Leader in Andrew Heliax and
Times Microwave LMR Tm and others.
peripherals. www.davisRF.com
Tel: 1-800-328-4773 (1-800-DAVIS RF) Tech'l: 1-978-369-1738, Fax:
1-978-369-3484
~ DAVIS/ORION Marine Wire and Cable Co., Distribution and
Design:
UL/USCG Marine Stds.
~ Orion Wire Corp., Design Engineers of Specialty/Custom Cable
Tel: 1-800-328-4773, 1-603-787-2200 Fax 1-603-787-2221,
email: Orion@connriver.net
www.davisRF.com
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