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

[Roger (K8RI)]

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.

73

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.  
>
>   
>