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<p>Bom dia<br>
</p>
<p>Acho piada a estes esquemas onde se usam cabos coaxiais... x cm,
y comprimento mas nunca se refere o factor de velocidade do cabo
usado e depois dá asneira. <br>
</p>
<pre class="moz-signature" cols="72">73, Gomes op: CT1HIX
<a class="moz-txt-link-freetext" href="https://ct1hix.net/">https://ct1hix.net/</a></pre>
<div class="moz-cite-prefix">Às 11:14 de 05/08/19, João Costa >
CT1FBF escreveu:<br>
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<p style="margin:0px 0px
1em;padding:0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;font-family:inherit;vertical-align:baseline;box-sizing:inherit;clear:both">I'm
trying to build a 1/2 wave "Coaxial J-Pole" antenna,
similar to what is described <a
href="http://members.upc.nl/a.vrijswijk/documents/42.html"
rel="nofollow noreferrer"
style="margin:0px;padding:0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;font-family:inherit;vertical-align:baseline;box-sizing:inherit;color:rgb(44,87,119)"
moz-do-not-send="true">here</a>:</p>
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1em;padding:0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;font-family:inherit;vertical-align:baseline;box-sizing:inherit;clear:both"><img
src="https://i.stack.imgur.com/D2EMX.jpg" alt="Coaxial
J-Pole" style="margin: 0px; padding: 0px; border: 0px;
font-style: inherit; font-variant: inherit;
font-weight: inherit; font-stretch: inherit;
line-height: inherit; font-family: inherit;
vertical-align: baseline; box-sizing: inherit;
max-width: 100%;" moz-do-not-send="true"></p>
<p style="margin:0px 0px
1em;padding:0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;font-family:inherit;vertical-align:baseline;box-sizing:inherit;clear:both">Such
an antenna would be great for stringing up in a tree
when operating remotely, no tuner needed.</p>
<p style="margin:0px 0px
1em;padding:0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;font-family:inherit;vertical-align:baseline;box-sizing:inherit;clear:both">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.</p>
<p style="margin:0px 0px
1em;padding:0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;font-family:inherit;vertical-align:baseline;box-sizing:inherit;clear:both">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.</p>
<p style="margin:0px 0px
1em;padding:0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;font-family:inherit;vertical-align:baseline;box-sizing:inherit;clear:both">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?</p>
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