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Re: [TowerTalk] Cable loss revisted.

To: "Tower and HF antenna construction topics." <>
Subject: Re: [TowerTalk] Cable loss revisted.
From: jimlux <>
Reply-to: "Tower and HF antenna construction topics." <>
Date: Fri, 05 Feb 2010 06:48:39 -0800
List-post: <">>
Jim Thomson wrote:
>   I visited some contest stations, and after having a look at things,  cringe 
> at the thought of the loss on the coax cables used. 
> Some had really long runs of coax from station to base of tower.. then more 
> up the tower, etc.  300-400'  was typ. 
> Biggest cables used were 1/2" heliax.     A lot of it was 213-U    Some was 
> LMR-400 or eq. 
> I don't see why one would want to try and squeak out another .5 db  of gain 
> on a longer boom yagi,
> [ then repeat on every other yagi].. then turn around and lose a whole bunch  
> from the long run's
> of coax being used !!   Sure... 1db  doesn't  sound like much.. but  that's 
> 21% of ur power gone.... and it
> drives me nuts to think I burned up 21% of the power coming out of the  
> linear.   That equates to 472 watts
> burned up.  [ 2250w pep out  x .21 = 472 w] 

Ham contest stations aren't the only folks who do this.  They do the 
same thing on spacecraft link budgets.. obsess about another tenth of a 
dB in coding gain to get ever closer to the Shannon limit, or agonize 
about tenths of a dB in power amp end-of-life output power, and then put 
the Xband antenna at the end of 6 ft of coax which has 3 dB of loss.


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