[TowerTalk] T-match?

[i4jmy@iol.it]

Why the low feedpoint of a 5 elements yagi has to be transformed into a 
targeted 200 Ohm impedance is a bit obscure to me.
May be you plan a log cell structure as the driven element ?
In any case, if you drop YO and chose instead AO (or any other generic 
wires software), you can model almost any type of match threating it as 
symple wires and loads and beeing nearly shure that your model (if 
accurate) will work closely in practice.
When a multi element yagi is modeled to maximize gain and F/B the 
driven element feed point impedance actually lowers as well the BW.
Unfortunately, the gain figures realated to low impedances are not real 
because of the unavoidable resistive losses and any frequency dependent 
matching device inserted in a low impedance tend to take part in 
worsening the losses and narrowing the band. 
As well as a low feed point impedance insures losses and so a real gain 
that's lower than desired, a T match to rise up a low impedance to 200 
Ohm looks to be not the good solution. 

73,
Mauri I4JMY


> ---------- Initial message -----------
> 
> From    : owner-towertalk@contesting.com
> To      : towertalk@contesting.com
> Cc      : 
> Date    : Thu, 15 Jun 2000 09:00:50 +0300
> Subject : [TowerTalk] T-match?
> 
> 
> Hi folks,
> I am new here, but I could not find anybody discussing about T-
Matches;
> It is an antenna term, but antenna issues seem to have been discussed 
here
> quite a lot; not so much on antennaware reflector.
> 
> I have now a successful design based on YO6.5 + a lot of tweaking
> on my 4 el 15m yagis at my OH0V conetsting site, but I would like
> to build 10 m setup with less hassle & tqweaking.
> 
> So, if anyone would happen to have T-match and radiator element 
dimensions
> for example to the yagis described in ARRL Antenna Book, chapter 11, 
page
> 19,
> or any other 5 element designs, I could try to simulate the model with
> YO in order to find best possible starting point to tweaking.
> 
> Target impedance for the fee
nced.
> 
> 
> Thanks + 73,
> jukka (OH6LI)




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