[amsat-bb] LMR-400 direct to antenna or no?
Edward R Cole
kl7uw at acsalaska.net
Sun Apr 3 09:06:13 UTC 2016
I can support what Greg stated.
I have ten foot of LMR-400UF to go around my az-el system between my
Relay/Preamp box and the 4-way divider that feeds my four 2m-eme
yagis (21-foot long booms). There is another 18-foot of LMR-400 to
each yagi so plenty of coax loss even in an eme array. I figure my
loss from antenna to preamp at 0.45 dB.
I get away with that much loss because my preamps are 0.1 dB NF vs
the typical satellite preamp that has 0.5dB NF. My overall Rx system
NF is est. 0.57 dB.
on my 6m long-boom yagi I have about 2 turns of LMR-400 that wind
around the mast before connecting to my relay/preamp box. This
allows enough flex not to break the LMR-400. Ten foot of LMR-400UF
would not be significantly more loss so up to 2m it should work
fine. The real key to getting good Reception is the preamp at tower
top. Most 2m radios have NF of 6 to 10 dB. Transverters are better
at about 1.5-2 dB NF. But both benefit with a preamp close to the antenna.
I think there is a recent version of Belden 9913 which has solid foam
core vs the polyethyline spiral bead with air core that was so
susceptible to moisture. I think its called 9913F.
But I use LMR-400 as its about the same cost and much better with
moisture if you do good sealing at the connectors.
73, Ed - KL7UW
From: Greg D <ko6th.greg at gmail.com>
To: w4upd <updwrb at bristor-assoc.com>, amsat-bb at amsat.org
Subject: Re: [amsat-bb] LMR-400 direct to antenna or no?
I understand the desire for minimal use of connectors, but the coupling
between the rigid cable coming from the shack to the rotor, and the flex
cable going to the antenna, is a good place to put a nice little
preamp. Think of it as a barrel connector with attitude. Yes, putting
it at the antenna feed point is better, but unless you're working EME,
the practical difference is pretty small.
Your luck with 9913 and water ingress is significantly better than mine
ever was. I had one 60' run that kept getting worse over time. It got
so bad that I drilled a hole in the lower end connector so I could suck
out the water until I could find some hardline to replace it. Never
used the stuff ever again.
73, Ed - KL7UW
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