[TowerTalk] Radio Shack 300 Ohm Line Characteristics

[Bill Tippett <btippett@alum.mit.edu>]

        I'm planning to try an 80m dipole fed with Radio
Shack 300 ohm twin-lead for Field Day.  I only plan to
run QRP so power handling is not a consideration.  In
using the method on p.34 of April 2004 QST, I am first
using Eznec to determine feedpoint impedance for each
band (80-10m) and then plugging that into TLW (N6BV's
transmission line analyzer) to look at line loss issues.

        The data N6BV has loaded into TLW for "300
ohm tubular" line does not seem right for the RS feedline.
It show loss of 0.541 dB/100' at 28 MHz, but 450 ohm
ladder line shows loss of 0.146 dB/100'.  Since the
300 ohm line uses foam insulation between conductors,
I'm finding it hard to believe there is so much difference
in losses.  The RS feedline appears to be of fairly high
quality, with a heavy-duty brown polyethylene covering
two stranded #20 wires with foam insulation surrounding
and between the wires.  This is not the junky white stuff.

http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=15-1175

        I have searched high and low for some believable
loss numbers (20th edition Antenna Book, Wireman's
Wirebook IV, Internet, etc) but have come up empty so
far.  Has anyone actually ever measured the Radio
Shack Twinlead or does anyone know of published loss
figures for this type of twin-lead?

			73,  Bill  W4ZV

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