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Expecting a 40 meter antenna to "work" when mounted directly above and at low heights above a metal or concrete (probably with reinforcing rod) roof is an unreasonable expectation. The dealer, exhibiting a knowledge of antenna theory and application, was indeed correct. I would expect the impedance to be much different than the needed 50 ohms and the pattern would also vary dramatically from what is expected. Furthermore, how do you know the antenna didn't work? The antenna could have been "working" but showing a high VSWR due to the mis-match caused by the roof. Since you spend much time modeling, I would think you could recreate just what is happening with an antenna's impedance mounted at very low lambdas above a metal counterpoise. The logic behind the dealers recommendation is sound as well as the design of the antenna. The logic behind your installation and expectations escapes me! Natan W6XR/2 FORCE 12 East Ithaca, NY ----- Original Message ----- From: kk <kk@cg.yu> To: Alex (Tex) Ihasz <vk1tx@one.net.au>; Force 12 Reflector <Force12Talk@qth.com> Sent: Wednesday, March 08, 2000 9:36 AM Subject: Re: [Force 12 Talk] re C4S > C4SXL did not want to tune on 40m, while on contespedition in Cyprus. The > contest ended with inverted V for 40m band. However, P3A team used C4XL with > satisfactory results. European dealer suggested we do not put the antenna > above metallic or concrete roof. Well, we questioned this logic, since flat > hotel roof was ideal for this antenna... Everything was double checked, > separate feedline as required, but still no SWR dip less than 3:1. > > 73 Kele > 5B4/4O6A > > -----Original Message----- > From: Alex (Tex) Ihasz <vk1tx@one.net.au> > To: Force 12 Reflector <Force12Talk@qth.com> > Date: srijeda, 08.03.2000. 11:59 > Subject: [Force 12 Talk] re C4S > > > >Hi All, > >Will be purchasing a Force 12 C4s Yagi at Dayton this year. > >Can anyone give some information re the performance on 40m and any > >problems with the 2 feed line system of the yagi? > >Tower height is only 55ft. > >Cheers, > >TEX VK1TX > >email: vk1tx@one.one.net.au > > > > > > > > > >-------------------------------------------- > >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 force12@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 force12@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 force12@qth.com |
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