My choice would be, BuryFlex(TM) up the crank up tower. Although stiff,
regular LMR 400 and 600 can be used for rotator loops. Use a 3 turn coil
(coiled like a clock spring) laying on a flat plate or grid at the top
or just below the top of the tower. I would orient the antenna so at
one extreme of rotation the coil would be nearly the full 3 turns. going
to the other extreme, would tighten the coil a bit The coil would be a
minimum of 2 to 3 feet in diameter. This should produce very little
bending of the coax.
BuryFlex(TM) is more flexible, has a very tough jacket that is also
smooth and depending on the supports can be very slippery.
However, even using the same kind of coax all the way, I'd still make
the rotator loop a separate piece as it is the place that is likely to
give the most problem. Record the length so you can make a new one if
ever needed. That way, you make a new jumper and just replace the old one.
Remember if this is on a tilt over with a tilt plate to leave enough
room for the antenna to clear the loop support. Maybe even make a tilt
fixture for the loop support. It needs to tilt, but also needs to clear
a section of tower.
As my station is located on the S side of the shop about 1/3rd of the
way down the wall to the W end.Currently the coax inside the shop goes
from a patch panel directly behind the rig about 4' above the floor,
then up through 1.5" EMT abt 6 feet and then over an insulated door to
the W wall. It now comes back down 6 feet and goes N abt 14 feet where
it goes through the W wall to a weatherproof box and to the AV640.
The plan is to "T" off the where the 1.5" EMT drops down 6' and add a
horizontal 1.5" EMT across the W end of the shop with a sweep 90 onto
the N wall. Then a sweep 90 down about 10' E of the W wall into a box
about 3' above the floor, through the wall into another weatherproof box
from there it's down through 2 or 3" PVC and underground to the tower
that makes an overall run of "about 88 feet.
I may run BuryFlex all the way, but I have two 200 foot coils of LMR
600UF left. I've been running the UF stuff through the underground and
interior conduit where it never gets hot or exposed to UV. Other than
being a PITA to install connectors on, I figure the UF should last a
long time in conduit. OTOH It's not a long run and BuryFlex would be
easier to pull. I'll mount a box on the side of the LM470 like I did on
the 45G
I purchased a bunch of 600UF just before I found out what poor shape my
LMR400UF jumper / rotator cables were in. Fortunately I had a 1000 ft
of the regular LMR600.
There is a run of 1/2" EMT containing two 120 VAC circuits within a foot
of where the coax will go through the wall, so I'm thinking of tapping
off that for 120 VAC and mounting a weatherproof outlet on the outside
wall, or going through the weatherproof box with 1/2" PVC conduit along
side the conduit with the coax and rotator cables. Still undecided on that.
73
Roger (K8RI)
On 8/1/2015 8:16 PM, john@kk9a.com wrote:
I would never run one piece of coax underground that far and then up the
tower, especially with a crank-up. The tower piece will likely get damaged
at some point. LMR600 is not that flexible and certainly would not be good
for your rotator loop. I would direct bury large Heliax underground and
then use something flexible and tough (like Belden 8267) on the crank-up
tower.
John KK9A
To: "<towertalk@contesting.com>" <towertalk@contesting.com>
Subject: [TowerTalk] LMR600 up to the top of tower ?
From: Robert Harmon <k6uj@pacbell.net>
Date: Fri, 31 Jul 2015 17:43:18 -0700
I have a 380 foot coax run to the top section of my motorized tower when it
is
fully extended.
I am changing out all my old RG213 and thinking of saving a few db by going
to
LMR600 up to the top section then
LMR400UF up from there for the rotor loop and up to the 40 meter beam and
triband/warc beam on the mast.
What do you think of LMR600 for this run from the shack up to the top
section
for a motorized tower ?
When I lower the tower I am thinking I could coil the LMR600 into maybe 5
foot
diameter coils on the ground.
BTW the tower is 90 feet to the top of the top section when all the way up.
Is this a bad idea ? (I am hoping to avoid the cost of the flex LMR600UF if
I
can.)
A side issue is I understand I have to be very careful not to nick the
copper
clad on the center conductor
when installing a connector on the non flex LMR600. I would use the Davis
PL259 connectors for LMR600. Anyway maybe this usage of the
LMR600 is not a good idea, what do you think ?
Bob
K6UJ
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73
Roger (K8RI)
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