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Re: [TowerTalk] Coax Loss -- RG-Numbers Don't Tell us Much

To: "Tower and HF antenna construction topics." <>
Subject: Re: [TowerTalk] Coax Loss -- RG-Numbers Don't Tell us Much
From: "Roger (K8RI)" <>
Reply-to: "Tower and HF antenna construction topics." <>
Date: Fri, 05 Feb 2010 01:05:44 -0500
List-post: <">>

Jim Brown wrote:
> On Thu, 4 Feb 2010 10:38:19 -0800, Rick Karlquist wrote:
>> This is *generally* true, if comparing all copper cables.
>> But even in that case, the HF loss is not proportional to
>> DC resistance when comparing different sizes of cable.
>> And all bets are off when copper plating is involved.
>> It is also worth noting that Al has something like 1.6 times
>> the DC resistance of Cu but only 1.3 times the RF resistance.
>> Finally, 75 ohm cable has considerably more DC resistance than
>> 50 ohm cable with the same RF loss.
> Rick,
> My point is that virtually all transmission line losses at HF are I squared R 
> losses. 

That's why you want to install the largest coax you can afford.


Roger (K8RI)
> What R is will depend on the materials, and how they are affected by 
> skin effect. The equations on the LMR website that attempt to define loss are 
> first approximations of reality. Like any equation, it is based on certain 
> assumptions, and errors develop when those assumptions aren't exactly true. 
> Like 
> copper coated AL, copper coated steel, and a shield that is a combination of 
> AL 
> and copper braid.  

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