On 3/10/2012 5:14 PM, Hisashi T Fujinaka wrote: > I think the advantage (not magic) is that you get less loss in ladder > line than you do through the dielectric of coax.
FALSE! For all practical purposes, there is NO dielectric loss in coax below about 500 MHz, where it just BEGINS to show up. Virtually all the loss in any dry transmission line at HF and VHF is due to simple Ohm's Law in the copper (including the increase in resistance due to skin effect). It's all I squared R loss. The advantage of open wire line is solely the result of their higher IMPEDANCE, which means that for a given power level, the CURRENT is much less. For the same reason, 75 ohm coax has a bit less loss than 50 ohm coax for the same conductor size. So-called WINDOW line loses this advantage when it gets wet, because then it DOES have dielectric loss. BTW -- when you're analyzing these things, you must consider the heat produced in a common mode choke when the antenna has a lot of imbalance. An off-center fed antenna has a LOT of imbalance. 73, Jim Brown 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
