In a message dated 2/20/07 5:18:23 PM Eastern Standard Time, [EMAIL PROTECTED] writes:
> Even simpler is a 80m dipole fed with balanced line to a tuner for all band > use. The window line is less costly than coax. A good quality tuner is > less lossy in multiband use than coax/ tuner balun, etc.. Balanced antennas > have fewer problems than off center feeds. Balanced line to dipole does not > need a balun at the antenna. > In general, the above is true. But it's not always as simple as it is made out to be. First off, the classic lowloss open line numbers we see in the books are usually for lines with ceramic insulators and heavy wire - say, #14 spaced 4 inches with a ceramic spreader every couple of feet. Those numbers don't necessarily match those of common "window line" (Twin Lead with holes) and other parallel lines. Second, there are all sorts of tuners out there, and they're not all created equal. The Ancient Ones used big split-coil balanced tuners, which required a lot of cut-and-try. And if they were lossy, it was obvious because the coils would heat up at medium to high power levels. The modern single-ended-tuner-with-balun-at-the-output is a different animal. It can work well with some loads, and be a loss leader in others. At QRP levels, losses may not result in much heating, either. I read all sorts of stuff about recommended dipole lengths, but not much about feedline lengths. But what really matters is the overall system, and what impedance it presents at the shack end of the line at the frequencies of interest. A "good" antenna fed with the wrong line can present a shack-end impedance that is very low, very high, and/or very reactive. The tuner may match it, but it may not be very efficient. One excellent tool we have today that the Ancient Ones did not is antenna modeling software. Reg Edwards' simple DIPOLE3 gives a good idea of the actual efficiencies and losses of various dipole/transmission line setups. Free and easy to use. But it won't tell you how lossy your tuner or balun is. OTOH, don't let the search for the ideal antenna prevent you from putting up *something* and trying it out. 73 de Jim, N2EY ************************************** Check out free AOL at http://free.aol.com/thenewaol/index.adp. Most comprehensive set of free safety and security tools, millions of free high-quality videos from across the web, free AOL Mail and much more. _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net 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
