On 4/26/2014 8:21 PM, Mike Waters wrote:
You're right about the loss being all in the copper center conductor, Jim.
AND in the shield. One of the things that gives bigger coax lower loss
is that skin effect has the greater diameter of the shield to work with.
It's important to realize that "RG6" and "RG213" are no longer
specifications for the cable that we buy. There are, for example,
several dozen RG6s in the Belden catalog, many very different from each
other. Ditto for RG8, RG11, RG58, RG59, RG213, etc. You've got to look
at the mfr data sheets to find the real specs.
Example -- go to the Belden website and compare 9212, 8213, 9913,
9913UF. Very different construction, very different loss
characteristics. All "RG11" (although I've seen 9212 described as RG11
in older catalogs and RG6 in at least one newer one). I've got a big
spool of 9212, and it's slightly smaller than most RG11, but a lot
bigger than any RG6 I've ever seen.
I haven't seen Owen's charts, but there's a good chance they're out of
date in that respect.
For cables of approximately the same o.d. a pretty good determinant of
loss is DCR of the shield and center combined, because resistance at RF
is that DCR multiplied by skin effect. Cables with Cu clad Al, like
LMR400, are an exception. By the time you hit 2 MHz, it's equivalent to
solid copper. But NOT for Cu clad steel -- it doesn't get close to to
solid Cu for another octave or two. (an octave is double the frequency).
There's more detail about this in k9yc.com/Coax-Stubs.pdf
73, Jim K9YC
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