Re: [VHFcontesting] Pre-amp question follow up

[jeff millar <wa1hco@adelphia.net>]

You need a rotor loop to make enable the mast to turn without 
resistance.  It's difficult to make a loop with stiff coax and it ends 
up too big.  So the tower feedline changes over to something flexible to 
make the rotor loop, run up the mast, and out the boom to the driven 
element.  This  could be superflex, RG-213 or somthing reasonally 
flexible and low loss.  Avoid 9913 or other type of coax that can let 
water flow along the length.

I mount the rotor 10 ft below the top, with a 16ft high strength steel 
mast, but plan to push it up 5 more feet sometime.

The tower feedlines run up to the top of the tower to minimize the 
length of flexible (and small and more lossy) coax.

jeff, wa1hco


Michael A. Urich wrote:

> Original comment
>
> My vision is to run a single LMR-600 feedline to the top of the tower and
> then switch it to masthead pre-amps with LMR-400 runs to the antennas.
>
> * * *
>
> A point of clarification + a follow up question.  I haven't ruled out
> running a single feedline per band and the pre-amps do not have to be
> installed at the time the tower goes up, and due to budget limitations may
> have to come later but I want to plan for them when the tower goes up.
>
> One individual indicated that the LRM400 from the top of tower around the
> rotor is a bad idea because of its solid center conductor.  My intention
> is to have the rotor down inside the tower actually a few feet lower than
> my thoughts about where the weatherproof box for the pre-amps will go.
>
> My question(s) is Why would running a solid center conductor near the
> rotor be a bad idea?  And a follow up, If a solid center conductor is the
> improper approach then would running an even larger feedline past the
> rotor be incorrect as well?
>
> Mike Urich, KA5CVH
> www.ka5cvh.com
>
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>  

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