[Elecraft] Matching resonant antennas

Ken WA8JXM wa8jxm at gmail.com
Fri Jul 17 00:57:00 EDT 2020


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 <
elecraft at mailman.qth.net> 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 <
> forums at david-woolley.me.uk> 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:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to wa8jxm at gmail.com
>


More information about the Elecraft mailing list