|Subject:||[TowerTalk] Radio Shack 300 Ohm Line Characteristics|
|From:||Bill Tippett <email@example.com>|
|Date:||Sun, 13 Jun 2004 09:38:13 -0400|
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.
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
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
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