Bob, G3VVT wrote: Not sure that the statement that it would be rather lossy is correct as I have been led to believe that twin feeder is less lossy than coax and particularly the 50 ohm version. Even the 75 ohm hard-line coax as used by cable TV companies was always better than the 50 ohm coax in the loss figures for a given diameter cable. -------------------------------------------- Quite true about the relative losses, Bob. We've kicked this subject around here in the past. It's been pointed out that, while it is true that there are dielectric losses in feedlines, feedlines operating at high SWR's are more prone to resistive losses in the conductors than dielectric losses. Several people have pointed to the fact that the losses are directly proportional to SWR as shown in all the transmission line loss charts, suggesting that what the loss charts are showing are the increased ohmic losses occurring at the current maxima points (current loops) along the transmission line as the SWR increases. Voltages and currents do depend upon power, but low power does not guarantee low currents or voltages on a feedline operating with a high SWR. I melted a nylon banana jack running 15 watts! The jack was in a grounded panel connecting my ATU to a voltage-fed antenna. On the other hand, very high currents can occur at the current loop in a feedline operating at high SWR even at very low power levels. That's why "flat" feedlines having little or no standing waves are less lossy. The current and voltage are directly proportional to the power applied and do not swing through large extremes along the length of the feedline. Feedlines with larger conductors fare better in general. As you pointed out, "hard line" and other heavy duty transmission lines have excellent insulation. They also tend to have larger conductors with more surface area to reduce the resistance to the RF flowing along the surface. I count myself lucky to be able to use open wire line with #12 conductors. We all have to deal with compromises. But that's half the challenge of the hobby - finding the compromise that produces the best results! In my case it's no high supports nor length enough! (Great feedline, marginal antenna!)
A lot of modern telephones are incredibly RF-sensitive, having amplifiers and other circuits that have absolutely no RF protection. Your residual problem may be simply direct pickup by the phone wires of the RF signal acting as an antenna. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
