Current situation:
I have a Tasjian WT-51, fitted with "pass-through" style standoffs for
the transmission lines coming down the tower. Four runs of LMR-400 in a
bundle drop down through the standoffs, and form a loop near the base of
the tower. Then up and over the top of a shepherd's hook that is
fastened to the tilt fixture. As I crank down the tower, I arrange the
bundle on the ground in two loops. When the tower is all the way down, I
hang the bundle on the shepherd's hook so its off the ground.
Total length of LMR-400 for each antenna from the top of the tower to
the grounding block at the base of the tower is about 65 feet.
What I'm thinking about:
I have HF, VHF and UHF antennas on the mast. I'd like to upgrade two or
more of the transmission lines to something with lower loss. This
includes the runs on the tower as well as about 135 feet in conduit
running to the shack entrance panel. Roughly 200 feet total.
The LMR-400 is 1.5db/100ft at 150MHz and 2.7db/100ft at 450MHz.
LDF4-50A is half that.
I don't have any real experience with hard line. I do know it isn't
meant to be flexed repeatedly. There's a spec for that, even. CommScope
says at the minimum multiple bend radius of 5 inches, 50 bends typical,
15 minimum. Are those numbers higher for a larger bend radius? I don't
lower and raise the tower that often. A few times a year, usually for
severe weather here in FL.
Am I crazy to consider using LDF4-50A for the runs on the tower? It
represents about a third of overall system losses.
I've briefly looked at alternatives. LMR-600 is close in loss to the
LDF4-50A, but it seems harder to get and cost is higher. I don't know
about connectors. There is a "high flex" 1/2 inch hard line FSJ4-50 but
its loss specs are almost as bad as the LMR-400 and the multiple bend
spec is the same but at a much smaller radius (1.25 inches vs. 5 inches).
What else should I be considering?
TIA.
--
Art Greenberg
WA2LLN
art@artg.tv
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