[TowerTalk] 3000' feedline...can I make it work?

[Jim Lux]

----- Original Message -----
From: "Jim Lux" <jimlux at earthlink.net>
> The real bugaboo is the stranded aluminum vs the solid copper.  The
current
> will flow not only along the strands, but between strands, and that's
> through a semiconductive aluminum oxide layer.  Aluminum oxide is actually
a
> good insulator (and very low loss for RF), but the surface of a wire is
> probably a sort of composite of aluminum, aluminum oxide, and other stuff,
> and quite resistively lossy.
>
> So..... what condition is the wire in?  Can you do a quick test?  DC
> resistance won't tell you much, but if you were to rig up a 20-30 foot
test
> section of open wire line, you could measure the VSWR of a known mismatch
> and estimate the line loss (meter to balun to open wire line, to mismatch,
> then do same test with the mismatch at a different place, balun effects
> should be the same at both measurements)


One further idea on the RF loss of ACSR power wiring... Take a look in the
back of the NTIA report that just came out, and see what the folks in
Boulder used to model power line wiring in NEC4.  They've got the model
parameters there, and they probably put in a linear resistivity for the
power line.  Same kind of wire, I should think, as well as same frequency
range.  I doubt they just modeled  it as a perfect conductor.

Likewise, any of the other reputable analysis of PLC/BPL radiated emissions
modeling will probably have good working numbers for that sort of thing.
Perhaps the BBC studies? (Although I think they mostly looked at received
levels and didn't model the emitters).