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.
>
>
>
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