[TowerTalk] Double Coax Runs to Reduce Loss?

[Michael Clarson]

Perfectly clear. However, would the same math apply if the pair of cables
were treated as a shielded balanced line? I could see some applications for
that. --Mike, WV2ZOW

On Wed, Dec 21, 2016 at 1:12 PM, Jim Thomson <jim.thom at telus.net> wrote:

> Date: Tue, 20 Dec 2016 12:17:34 -0500
> From: "john at kk9a.com" <john at kk9a.com>
> To: towertalk at contesting.com
> Subject: Re: [TowerTalk] Double Coax Runs to Reduce Loss?
>
> It sounds like it work, at least until you do the math. Each run still has
> the same dB/ft loss.
>
> John KK9A
>
> ##  Assuming  lossless xfmrs at each end.  Loss in each coax run is
> identical.
> Total system loss is the same as a single coax..and no transformers.
>
> ## IE:  2 x  300 ft runs of  213 in parallel on 10m.   Assume 3 db loss per
> coax. Stuff 1 kw into the lossless xfmr... and u now have 500w into each
> coax.
> Each coax has 3 db loss... so only 250w  at each end of each coax.
> 250+250 = 500w.   Which is no different vs 1 kw into a single coax..with
> the
> same 3 db of loss, still = 500w.   Maths are the same on  TX...and also RX.
>
> ##  However  2 x coaxs in parallel will indeed handle double the TX power.
>
> ##  If this is for monoband  use, a simple L network  at each end will
> easily do the
> 50:25............ and  25: 50 ohm transformation...with virtually no
> losses.
>
> ##  Lossless L networks are typ made with  cu tubing +  NPO doorknob caps.
> That scheme works good for feeding 2....or  3  or 4   monoband yagis.
>
> ##  But for greater power handling capability.. just use bigger coax to
> begin with,
> then you also get the benefit of lower loss coax.  Lower loss coax is the
> ticket
> for both RX  + TX.....esp on long runs .
>
> Jim  VE7RF
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