In the Book one studies for the Amateur Extra book are tables of what occurs to voltage and current in the feedline. The graphed waves of voltage and current in the feedline are different for coax compared to ladder line. The graphs have tick marks every 1/4 wavelength of the frequency in use - and it is at these ticks where peaks and lows of voltage and/or current occur.
Thus you will also find tables at dxengineering.com recommending particular lengths of feedline for various bands. In addition I and many others have pruned the feedline (easy for ladder line) to obtain the best SWR. I have even seen on the internet a simple Antenna-TUNER project where one switches in various lengths of feedline using DPDT switches to find the best swr. One switch adds or takes out an 8 ft length of ladder line, another switch adds or takes out a 4 ft length of ladder line, another switch adds or takes out a 2 ft length of ladder line, and another switch adds or takes out a 1 ft length of ladder line. The vast majority of people just use a random length of feedline - whatever length was needed for the particular antenna installation. Last year I put up a Cactus-Super-J-Pole 2meter antenna for my winlink rms packet station. I just couldn't get a good SWR until I added an additional 8 ft of coax cable. (I just happened to have an 8 ft jumper laying around). To some, this is amazing magic. Howard -- View this message in context: http://n2.nabble.com/FW%3A--The-use-of-a-doublet-tp3258726p3259557.html Sent from the Elecraft mailing list archive at Nabble.com. ______________________________________________________________ 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
