Nothing "however" about it, Roger. Of course it's all skin effect, and
copper-coated or clad onto steel has much greater loss than solid or
stranded copper at these frequencies.
BUT - there's a big difference between copper-clad Aluminum and
copper-clad steel. RF resistance of copper-clad Al is NOT significantly
different from solid/stranded copper at any frequencies where we are
likely to use it.
Yes, at HF the most reliable comparative of cable loss below UHF is the
total resistance of their conductors at the frequency of interest. For
solid copper conductors, DC resistance can be compared, because
resistance at RF is a multiple of the DC resistance. For copper-clad Al,
the resistance of a solid copper conductor representative of the DC
resistance of the center. So -- there's nothing wrong with using LMR400
and other cables with Cu-clad Al center on the lower HF bands, except
that they are NO BETTER than a lower cost coax that provides the same RF
resistance. That's why my table in k9yc.com/Coax-Stubs.pdf lists coax
cables in order of their DC resistance, and why the last column in the
table is cost.
73, Jim K9YC
73, Jim K9YC
On Thu,8/4/2016 10:29 PM, Roger (K8RI) on TT wrote:
However on the lower frequencies, such as 160 and 75 skin depth plays
an important roll. I believe the flash plating as is found on steel
core, center conductors is insufficient to keep I^2*R losses down.
I'd avoid those cables with small, solid center conductors.
That brings to mind the question of LMR400 which has a "relatively"
large copper plated, solid Aluminum center conductor versus cables
like BuryFlex with stranded, copper center conductors. LMR-600 is
larger yet.
They give loss ratings per 100 feet, but what about 160 and 75 meters?
73
Roger (K8RI)
On 8/4/2016 Thursday 2:37 PM, Jim Brown wrote:
On Thu,8/4/2016 11:23 AM, Mike Fahmie via TowerTalk wrote:
power loss (I^R is usually negligible).
Mike,
Exactly the opposite is true -- below at least 300 MHz, loss in
transmission lines is ALL I squared R. Dielectric loss doesn't begin
to be significant until you're well into the UHF region.
73, Jim K9YC
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