Hi John,
I wouldn't use LMR 400 (or other large diameter LMR series cables) for any
situation where the cable will be flexed. Consider LMR 400 a poor man's
hardline, and treat it as such. This means it should be carefully unrolled
and installed into a stationary position, just like heliax or other
hardline. Pigtails, or short runs of flexible line with a stranded center
conductor (like RG-213 or Davis' FLEXI-4XL), should be used at both ends of
the LMR runs where flexing takes place. For example, the solid center
conductor LMR cable should end just below the rotator (near the top of the
tower) and RG-213 or FLEXI-4XL continue past the rotator and up to the
antenna. Do the same at the shack end, and continue with RG-213 to the
station where flexing will take place. Personally, I like the RG-213 for
these applications because of it's solid dielectric and toughness. Just
remember that the LMR cable should remain stationary after it's
installed. You'll be fine if you do this.
Oh, the losses (at HF) incurred using these pigtails are
inconsequential. Using some of the great methods espoused here on
towertalk, keep these splices waterproof and mechanically sound and
problems shouldn't develop.
At VHF, and especially UHF, these pigtail losses require a bit of
consideration. At these higher frequencies, RG-213 starts to become
lossy. Consider the FLEXI-4XL for those situations. Also, VHF or "PL-259"
connectors should be traded out with N-type connectors to reduce impedance
bumps and keep the losses down.
I'm sure others will add to this. 73!
Steve, KZ9G
At 02:01 PM 10/18/2002 -0400, you wrote:
><PRE>HI everyone , I have a question about lmr 400 I have 3 runs of this
>cable
>ready to be run up my tower next spring the cable is already buried. is the
>lmr 400 ok to connect to a yagi or other antenna on a rotating mast ? is it
>flexable enough? I am asking about a standard hook up . thanks John
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