Hi Thomas,
I know it was a lot of work, but you quoted dc resistance.
DC resistance and RF resistance are entirely different. Tables for
dc or very low frequency ac do not reflect the resistance at radio
frequencies. I'd hate for people to think the change in RF
resistance (what I was talking about) is as small as the change at
dc (which you listed)!!!!
In stranded wire, high frequency RF current only flows on the
outermost edge of each stand...it doesn't even flow on the inside
edge of outer stands (let alone the core stands)...so you can
imagine how thin the conductors "look" for RF (and much of the
energy in lightning).
Braided wire is even worse than stranded, because the current has
to cross over between thousands of tiny pressure connections as it
goes along a long length of braiding. The current always is forced
on the outside layer. When an outer lay turns in towards the
center, current tries to find a path back to the outside through
pressure connections at every single weave!
If the current is low, you won't notice any difference because even
multiplying loss several times in that case means nothing. In other
applications, the change can be significant. Like lightning
protection applications, or in short antennas carrying high currents.
It is also bad in tank circuits or RF inductors.
73, Tom W8JI
W8JI@contesting.com
--
FAQ on WWW: http://www.contesting.com/FAQ/topband
Submissions: topband@contesting.com
Administrative requests: topband-REQUEST@contesting.com
Problems: owner-topband@contesting.com
|