ARLA/CLUSTER: Antena J para os 10m simples

[João Costa > CT1FBF]

I'm trying to build a 1/2 wave "Coaxial J-Pole" antenna, similar to what is
described here <http://members.upc.nl/a.vrijswijk/documents/42.html>:

[image: Coaxial J-Pole]

Such an antenna would be great for stringing up in a tree when operating
remotely, no tuner needed.

The trick is that I'm trying to use 75Ω RG6 coax for the matching section
(because it is relatively inexpensive and low-loss), but I want a 50Ω
impedance at the feed point.

There are many single-stub matching network calculators, but almost all of
them assume that the impedance of the matching network is the same as the
feed point impedance. I know that such a matching network is possible
because that is exactly what the traditional j-pole antenna is: a
single-stub impedance transformer feeding a half-wave antenna, where the
matching section impedance doesn't match the feed point impedance.

Succinctly: How can I calculate the physical parameters of a single-stub
impedance transformer when the matching section impedance doesn't match
either the feed point impedance or the load impedance?
antenna-theory
<https://ham.stackexchange.com/questions/tagged/antenna-theory> impedance
<https://ham.stackexchange.com/questions/tagged/impedance> coaxial-cable
<https://ham.stackexchange.com/questions/tagged/coaxial-cable>
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