Hi, The terminated loss in a coax is half of the return loss looking into the unterminated cable. RL is easily calculated using the formula:
RL = 20 * log (VSWR+1)/(VSWR-1) (dB) The reason for the factor of two is that the wave has traveled the cable twice before being measured as return loss. But it is true that high SWR is diffucult to measure accurately so the method isn't used much. E.g. the LP100A is pegged at VSWR = 9.99 so cannot determine losses less than 0.87dB. The LP100A can also display the return loss directly but unfortunately that value is also pegged at the 1.74dB value corresponding to that SWR. AB2TC - Knut DL6OAP wrote > That kind of chart is e. g. in the ARRL antenna book (I have two older > editions but am sure it is in both of them). Since the measurement assumes > that the fraction of the power that is put into the line and not being > converted into heat in the coax is completely reflected at the far end, it > should work equally well with shorted or open end. I have a MiniVNA > network analyzer that relies on this method for determining the electrical > length and the loss of coax. Normally I leave the end open. > However, I am not sure if it works very well with short pieces of low loss > coax because of the difficulties of precisely determining a high s.w.r. > > 73, Ralf, DL6OAP > > Am 12.11.2013 um 14:47 schrieb "Charlie T, K3ICH" < > pincon@ > >: > <sni> -- View this message in context: http://elecraft.365791.n2.nabble.com/OT-Checking-coax-jumpers-before-soldering-tp7580727p7580765.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
