Yes, If you use the SWR plot given by EZNEC you can place your curser on
the frequency you're interested in and it will give you the impedance
calculated at that frequency. The source impedance is at the source not at
the end of the feedline so be careful. A transmission line will act as a
transformer unless the source is the same Zo of the transmission line or if
you are not the 1/2 WL multiple. I think you are overthinking your
problem David. But if you really wanted to get into the details you
could create a model that had the coax cable feeding your balun included in
the model and place your source at the radio end of your coax model.
Jay Terleski
Array Solutions
214 954 7140
On Mon, Mar 25, 2024 at 1:49 PM David Gould <dave@g3ueg.co.uk> wrote:
> Thanks to Jay and Joe for the Alternate Zo suggestion. It certainly
> gives the revised SWR curve I was expecting.
>
> I would also like to know the new impedance after the transformation,
> which the SWR graph does not provide the data at the bottom is always
> for the 50ohm plot and not the 200ohm plot.
>
> Is there a way to get this additional information? If not I will
> investigate the second of Joe's suggestions.
>
> 73,
>
> Dave G3UEG
>
>
>
> On 25/03/2024 18:23, Joe Subich, W4TV wrote:
> >
> > > I am mainly interested in the impedance transformation to the 50 ohm
> > > feedline coax.
> >
> > Why not just use Alternate SWR Zo = 200 Ohms? That will give you the
> > 50 Ohm SWR after the 4:1 "balun" assuming the balun is a broadband
> > current balun.
> >
> > Otherwise, you can use a second short wire, move your source to it,
> > and place a *1:4 transformer* between that wire and the location of
> > your original source.
> >
> > 73,
> >
> > ... Joe, W4TV
> >
> > On 3/25/2024 1:36 PM, David Gould wrote:
> >> I am using Pro/2 v 7.0.
> >>
> >> I have been through the EZNEC help and the test drive around the
> >> track, but the examples are all more complex than I am looking for so
> >> I am having trouble getting to the basics.
> >>
> >> I would like to model a variation of a centre fed dipole (over a wide
> >> frequency range) that has a 4:1 balun at its feed point. Is there an
> >> example anywhere I could use to copy from?
> >>
> >> Currently I am just using a straight wire with the source at 50%
> >> along. Can I develop from this or do I have to split it into two
> >> separate wires?
> >>
> >> I am mainly interested in the impedance transformation to the 50 ohm
> >> feedline coax.
> >>
> >> Any help would be appreciated.
> >>
> >> 73,
> >>
> >> Dave G3UEG
> >>
> >
> >
> >
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>
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