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because I get excellent agreement between the simulations and actual measurements for SWR and radiation patern. - Thor Hallen K5AGE -----Original Message----- From: Guy Olinger, K2AV [SMTP:k2av@contesting.com] Sent: Tuesday, October 24, 2000 9:03 PM To: Pete Smith; force12talk@qth.com Subject: Re: [Force 12 Talk] C3SS vs. C3S on 6 and 17 Meters Second Pete's motion. EZNEC cannot model a C3SS properly. Among a number of modeling issues are 1) EZNEC's level of NEC doesn't do well when conductors change diameter turning corners 2) doesn't like close spaced conductors of unequal diameter 3) the device for adjustments for tapered elements is based on a straight element design and doesn't figure in linear loading. If you want to pay the moolah to get NEC-4 (moocha bigga bux) you can verify it, but even then it takes a few careful tricks. W4RNL (equipped with every antenna modeling program know to man) is the only one I know who has done these. You can grab his attention on antennaware@contesting.com if you want a discussion on it. L.B. also has a lot of stuff on his extensive web page http://www.cebik.com/radio.html --... ...-- . ... --. .-.. Regards, Guy Apex, NC ----- Original Message ----- From: Pete Smith <n4zr@contesting.com> To: <force12talk@qth.com> Sent: Tuesday, October 24, 2000 9:00 AM Subject: Re: [Force 12 Talk] C3SS vs. C3S on 6 and 17 Meters > At 05:28 AM 10/24/00 -0700, Thor Hallen wrote: > >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 > > > -------------------------------------------- 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 -------------------------------------------- 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 |
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