Topband: question about matching network for short vertical RX antenna

[Matt Murphy]

I realized the attached Smith chart image did not come through on the
reflector so I posted it on the web, here is the chart:

https://www.dropbox.com/s/nwfqr6xhsfdgjjb/Screenshot%202017-03-09%2013.03.33.png?dl=0

73, Matt NQ6N

On Thu, Mar 9, 2017 at 12:46 PM, Matt Murphy <matt at nq6n.com> wrote:

> In preparation for the Stew I'm thinking of setting up a two element
> end-fire array aimed at Europe, and possibly another one aimed south.
>
> I've done some reading about these types of arrays and I think I understand
> the approach taken by W8JI in his design of the short verticals he uses, as
> well as the design of the YCCC short vertical.
>
> Just for kicks I decided to model a short vertical that used matching stubs
> made with RG-59.
>
> I'd like to ask for advice on this approach.  I would use the array on 160m
> only, and the objective is for it to have better RDF than my inverted L, so
> even a few dB would be helpful.
>
> I modeled a 6' vertical element in CocoaNEC and designed a matching network
> using SimSmith.I have attached the Smith chart of the matching stubs.
>
> In my CocoaNEC model, the feed point impedance does not change much if I
> increase the length of the element to 30', and the matching network is not
> sensitive to changes in the feed point impedance.  I wonder if this
> matching network might just be equivalent to matching the coax with no
> antenna connected (and if so what that means for the antenna's performance)
>
> Any advice on the antenna, matching network, etc., would be much
> appreciated.  My next step is to build one and verify that my real world
> results for a single element match the model's prediction, and if so, to
> subsequently build a second one and connect them with a phasing line to
> achieve end-fire directivity over the bottom end of 160m.
>
> Advice much appreciated.
>
> 73, Matt NQ6N
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