On 9/10/2011 11:05 PM, Gary Hinson wrote: >> Sure. Twisted pair is a VERY effective transmission line, and that is >> what is needed ... > Hey Jim, what kind of twisted pair could I use to feed my [mostly 50 ohm] HF > antennas? Coax is expensive in ZL so I'm willing to try alternatives. I'm > even thinking of homebrew balanced line with baluns at the bottom (a > coax-fed remote antenna switch in my case).
Coax is expensive in the US too :) The key to loss is conductor size and impedance. The parallel wire cable sold for use with loudspeakers would make decent parallel wire antenna line. Twisting has the advantage of greatly reducing crosstalk and radiation/pickup to/from the line. RG8 uses #14-#10 for the center conductor, most copper braid shields are equivalent to #10 at DC and a much larger conductor on the higher HF bands (thanks to skin effect). #12 parallel wires or twisted pair would probably be equivalent in loss to very good RG8, and in the 50-70 ohm range for impedance. At HF, dielectric loss doesn't matter, but the dielectric will affect Vf. You will need common mode chokes at both ends -- remember, most real world ham antennas are unbalanced by their surroundings. It's a mistake to call cable like this a balanced line. It's a parallel wire line or twisted pair line. 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
