Towertalk
[Top] [All Lists]

## Re: [TowerTalk] wire antenna question

 To: steve@karinya.net, towertalk@contesting.com Re: [TowerTalk] wire antenna question TexasRF@aol.com Fri, 14 Nov 2008 10:39:05 EST mailto:towertalk@contesting.com>
 ```Steve, when I plug your numbers into a transmission line program I get these results:283.8 -j23.66 = 5.72 vswr (same as your example). 288.2 +j0 = 5.7 vswr which is just slightly lower than example #1 but illustrates better vswr when j=0. I did not look into the 40 +j4 case but in general, real antennas show a reactance change much greater than a resistance change when they are in the range of one half wavelength. I would expect a reactance of maybe 20 ohms (positive) for an increase of 5 ohms in the resistive value. This would show a vswr of 1.55 which is higher than the 40 +j0 value of 1.25. Perhaps someone can model a dipole to confirm or refute this. 73, Gerald K5GW In a message dated 11/14/2008 3:54:59 A.M. Central Standard Time, steve@karinya.net writes: Be aware that there are some "extreme" cases where minimum VSWR and Resonance do not occur at **exactly** the same frequency. For example, if I take a 34ft folded dipole, and am silly enough to feed it through a 50 Ohm line, I get: Minimum VSWR: 5.72 @ 13.62 MHz where Z=283.8-j23.66 Resonance: Z=288.2+j0 @ 13.7 MHz where VSWR=5.76 It just depends how fast the resistive component is changing relative to the reactive component as you move away from resonance. Using the previous 40+j0 example, if away from resonance the impedance had become 45-j4 the SWR would have fallen from 1.2 to 1.1, not risen. This rapid shift of the resistive component tends not to happen on simple antennas like dipoles, but can occur in more complex arrays. 73, Steve G3TXQ _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk **************Get the Moviefone Toolbar. Showtimes, theaters, movie news & more!(http://pr.atwola.com/promoclk/100000075x1212774565x1200812037/aol?redir=htt p://toolbar.aol.com/moviefone/download.html?ncid=emlcntusdown00000001) _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
 Current Thread [TowerTalk] wire antenna question, Blair S Balden Re: [TowerTalk] wire antenna question, Terry Conboy Re: [TowerTalk] wire antenna question, Blair S Balden Re: [TowerTalk] wire antenna question, Terry Conboy Re: [TowerTalk] wire antenna question, TexasRF Re: [TowerTalk] wire antenna question, Blair S Balden Re: [TowerTalk] wire antenna question, Terry Conboy Re: [TowerTalk] wire antenna question, Steve Hunt Re: [TowerTalk] wire antenna question, TexasRF <= Re: [TowerTalk] wire antenna question, Steve Hunt Re: [TowerTalk] wire antenna question, Steve Hunt Re: [TowerTalk] wire antenna question, Jim Brown Re: [TowerTalk] wire antenna question, Blair S Balden Re: [TowerTalk] wire antenna question, Bob Nielsen