[TowerTalk] T-match?

[jukka.klemola@nokia.com]

Hi,

I am not looking excactly after higher feedpoint impedance,
it is one point of interest, yes; but easier construction,
better balancing and more 'selective' way of feeding the
antenna are the real targets.
For example a cut driven element is far less attenuating at third
harmonic.

I modelled also with EL & EZNEC, even getting into very short
lenghts of tubing did not model the impedances right.
I did not check this with AO, though. I think they use very much
the same 'engine' to do the simulations so the simulation performance
should be somewhat similar.

73,
jukka (OH6LI)

> -----Original Message-----
> From: EXT i4jmy@iol.it [mailto:i4jmy@iol.it]
> Sent: 15 June, 2000 14:25
> To: towertalk@contesting.com; jukka.klemola@nokia.com
> Subject: Re: [TowerTalk] T-match?
> 
> 
> 
> 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. 

I guess the current at the center of the driven element is high
anyway although there is no connector present with a T-match.

> 
> 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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