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>I recently put up a C3SS and everything performed as expected except SWR on >17 meters was very high and beyond the capture range of my automatic >antenna tuner. I suspected that it had to do with the linear loading used >by the C3SS so I created EZNEC models for the C3SS and C3S for comparison. >As expected, the EZNEC simulations confirmed the high SWR of the C3SS ( >>50:1 ) on 17 meters compared to <10:1 with the C3S. The C3S is able to >function on 17 meters because the full length elements on 20 and 15 >compensate each other and average out close to 17 meters. The linear >loading of the C3SS behaves like a trap on 17 meters disrupting the >compensation. Assuming the C3SS loading wires behave like traps at high >frequency, I noticed that the 20 meter element segments closest to the boom >should resonate near 6 meters. EZNEC predicted a very low SWR ( <2:1 ) at >51.5 MHz and this was confirmed by actual measurements on my C3SS. The 6 >meter performance is surprising good with a maximum gain near 10 dBi at 50 >MHz. I was thinking about converting my C3SS to a C3S but the C3SS is so >good on 6 meters that I will keep it. I have confirmed the 6 meter >performance in practice and verified the excellent gain and F/B, F/S >ratios. How's that for serendipity? Pretty neat. Just a word of caution, though -- I have found that my EZNEC models of the C-3 and C-3E require special care to get the gain figures to converge, and even then the feedpoint SWR predictions are not borne out by operating results. W4RNL suggested that the problem is due to the close spacing of the elements in the driven cell, and I suspect a similar issue might be present in modeling the linear loading. For the driven cell, LB suggested I try to get the segments to line up -- I find 40 segments for the 20-meter element, 30 for the 15-meter, and 20 for each of the 10-meter drivers yields fairly good convergence, even on 10 meters. Using the EZNEC-recommended number of segments, even the "conservative" recommendation, gives far different gain numbers. I've never tried higher frequencies, such as 6 meters. 73, Pete Smith N4ZR Contesting is ... Extreme Radio The World Contest Station Database is back up and running at http://www.qsl.net/n4zr -------------------------------------------- Force12Talk mailing list provided as a service by Force 12 Antennas, Inc. Force 12 Web site: http://www.qth.com/force12 Submissions: send to Force12Talk@qth.com To unsubscribe: send a blank e-mail to Force12Talk-leave@qth.com Force12Talk Message Archive: http://www.qth.com/force12/list/force12talk For problems with the list, contact n4zr@qth.com |