Actually it is not difficult to measure the SWR (or impedance) of an antenna at its feedpoint. Remember that an electrical half wave transmission line repeats the impedance at the far end, so I keep a half wave of RG-8x for many bands especially for this purpose (the number of bands grows as I add antennas).
Determining the elctriical half wavelength is not difficult with and antenna analyzer - start with a cable longer than the length needed and just prune for the length until the reactive part of the imedance goes to zero - Theroretically, that can be done with the far end of the line either shorted or open, but my MFJ259 has trouble properly indicating impedances greater than 650 ohms, so I use the shorted far end and cut the line for R=0 and X=0 or as close to that as I can read. Connect the half wave line to the antenna feedpoint and the analyzer will read the actual feedpoint impedance of the antenna. It is a neat way to tune single band antennas to match the feedline that you intend to use. The impedance of the half wavelength line is not critical - use any coax that you have available, it does not have to be the same as the feedline that you will eventually use. 73, Don W3FPR > -----Original Message----- > > The SWR at the rig end is not an accurate indication of the actual SWR on > the line, even if the SWR meter is put at the end of the coax after the > tuner. That's because the SWR at the rig end will always indicate > lower than > the actual SWR at the antenna end of the feedline due to the losses in the > feeder. To assess losses accurately, the SWR must be measured at > the antenna > end of the feeder. That's usually not so convenient to do. > _______________________________________________ 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
