So pruning a horizontal dipole will never provide a 1:1 SWR except at 0.18 wavelength above ground (the ONLY elevation where the radiation resistance is 50 ohms)? About 97 ft for 160m, 24 ft for 40m, 6 ft for 10m? A dipole a half wave above ground has a 70 ohm radiation resistance and therefore a 1.4:1 SWR is the absolute best?
Ken WA8JXM On Thu, Jul 16, 2020 at 6:52 PM John Magliacane via Elecraft < [email protected]> wrote: > On 15/07/2020 20:30, Ken WA8JXM wrote: > > > Conversely, a non-resonant antenna can have a 1:1 SWR. > > On Thursday, July 16, 2020, 03:33:12 AM EDT, David Woolley < > [email protected]> wrote: > > > You can only have a 1:1 SWR at a single impedance. If the design > > impedance is purely resistive, that means you can only have 1:1 for a > > resistive and therefore on-resonance load (or one that can be treated as > > having no reactive behaviour at the frequencies of interest - e.g. an > > ideal dummy load). > > I agree completely, but there's a "catch". > > Traveling-wave antennas, such as Rhombics, or Beverages, or leaky > transmission lines, are, technically, non-resonant. However, they can each > present a 50 ohm feedpoint impedance that is purely resistive, and produce > a 1:1 VSWR as a result. ;-) > > So, whether an antenna is resonant or non-resonant isn't the issue. The > issue is whether or not a load impedance contains a reactive component. If > it DOES, then it can never produce a 1:1 VSWR. > > > 73 de John, KD2BD > > ______________________________________________________________ > 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 > Message delivered to [email protected] > ______________________________________________________________ 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 Message delivered to [email protected]
