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Re: Coax Selection


I did this with my satellite coax runs.  I had two 1/2 inch hardline runs
along with my rotator cables.  I used a regular power weather head which
has a removable top for access along with a plastic portal with knockouts
for the coax to pass through.  It is easily caulked around the openings to
keep varmits out.  I ran the coax through the attic and down to the
basement via a return air duct between the studs in the wall.  I used this
route because it contained no fire break halfway down the wall.  I exited
in the basement and turned back up again into the wall behind my radio
desk.  The half inch coax was entirely inside with short flexible runs
beginning just inside the weather head for a fifteen foot run to the
antennas and again in the basement for the short runs to the rigs.  This
worked beautifully for many years and the 1/2" coax is as good as new.

However I was concerned about two things.  I suspected that if I ever took
a direct lightning stroke on the antennas, the stuff was going to follow
that solid aluminum jacket into the attic, etc. where it could easily start
multiple fires.  In addition, since I am getting a bit older now and can't
climb around in the attic as I used to be able to do, I thought it might be
a good time to get the coax run outside again.  This was influenced by the
eventual roofing job I will need when I can also replace the plywood
section where the hole is.  So I bought a couple of runs of Times LMR-600
coax and added a few feet by running it on top of the roof to the edge and
down the side of the chimney through metal brackets fastened into the brick
mortar.  I entered the basement wall through a 3 inch pipe with a 45 degree
downturn on the outside and turned up to the shack through the same holes
as before.  The run is 70 feet.  The total loss at 435 is 1.2db.  I did
move the preamp from the shack end to the antenna end of the coax and the
signal was improved over the old setup.  The antenna grounding lead is a
stranded piece of #4 cable running in parallel with the coax and rotator
cables to a ground rod just beneath the cable entrance through the basement
wall.  The 3 " entrance pipe was stuffed full of fiber glass insulation and
the outside end filled with silicone caulk.

Your run sounds like it is so short that I doubt you will see any
difference regardless of the path you choose.  I'd take the easiest one to
maintain, especially at my age :-)

"David M. Tipton, Ph.D." wrote:
> I am going to go pick up some coax this weekend (Or maybe even tomorrow at
> lunch) for my sattelite antennas.  The plan is to cut a whole in the roof,
> mount a "Vent Pipe" with an angled end (Looks like an upside down J) and run
> the coax through this, and run the coax the 5 feet across my attic and down
> through the wall into the shack.  (I have a 1 story home.)  The total
> distance from the antenna mount to my rig, is about 30 feet.  I figure on
> adding an additional 20 feet to compensate for errors in calculations and
> for rotation.
> This means that my total run will be around 50 feet.
> I want to know, on a run this short, what are my best cost/performance
> options?  Will 9913 work well?  Or Just Well Enough?  Would I be wasting my
> money going to something like LMR400?  Would I gain anything worth noting by
> going to LMR 600?
> Am I overlooking any other obvious choices?
> These coax runs are to feed the UHF and VHF Sattelite antennas btw.
> Dave
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73, Roy

Internet: w0sl@amsat.org
Home Page: http://home.swbell.net/rdwelch
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