On Sun, 04 Apr 2010 20:46:21 GMT, Owen Duffy wrote:

Bob wrote in
:

Anyone know the velocity factor of JSC #1317 450 ohm line, 18 AWG?
Googling seems to give a variety of answers, and it's not posted at
the JSC site.

Wes, N7WS, measured some Wireman lines similar to that above. His
measurements indicated Zo quite different to nominal, and velocity factor
around 0.9.

For applications where velocity factor is important, eg the 'matching
section' of a G5RV, I suggest you measure the actual cable.

I'm plugging the velocity factor figure into Cecil's program for
optimum feedline lengths on a multiband dipole, IMAXMIN.EXE. Given the
approximate nature of this kind of feed, a ballpark figure is probably
okay.

Bob
k5qwg


Wes's data is included in TLLC (http://www.vk1od.net/calc/tl/tllc.php).
Your cable has similar stranding to Wireman 551, but velocity factor will
depend on the detail of the dielectric extrusion and punching. If JSC is
the manufacturer, they may even be the source of Wireman lines, in which
case Wes's data may be directly applicable.

I have reservations about the adequacy of copper cladding on the cable
such as yours at the lower end of HF.

Owen