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@telus.net> wrote:
> Date: Tue, 20 Dec 2016 12:17:34 -0500
> From: "john@kk9a.com" <john@kk9a.com>
> To: towertalk@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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