Originally Posted by John Smith

Ian Jackson wrote:

This is an example of the 'traditional' 9:1 impedance transformer which,
on most MW and SW frequencies, gives a better match between the antenna
impedance and a 50 or 75 ohm receiver input impedance. On relatively
narrow bands of frequencies where the antenna impedance is naturally
lowish (where it is near odd multiples of a quarterwave), the match will
actually be made worse than if the transformer were not used. This
obviously depends on the physical length of the antenna. In the diagram,
the antenna length shown is 33m (say 100'), which is not far short of a
quarterwave on 160m. However, on the MW band, and on various parts of
the SW band, the transformer should improve reception.


Actually, the antenna terminals for the HF bands is marked "500 Ohm" on
my S350DL, 9 X 500 = 4,500 Ohms (the transformation I would expect from
a 9:1.) However, the author did claim an improvement of a number of
S-Units on his S350DL. This made me wonder, since I didn't want to
build it to see what was up, I just passed it along. I would not call
the author a "liar" without absolute confirmation ... who knows, perhaps
his "antenna arrangement" has resulted, somehow, in the end of that
(actually off center feed point) being 4,500 Ohms--perhaps Grundig lied
and the antenna terminals do exhibit a 50 Ohm impedance--I am lazy ...
some youngster can figure it out ... ;-)

I note that the writer correctly stresses that that the transformer is
an 'UNUN' (an accurate - but ugly - word).

Actually, I would not refer to it as an UNUN. A balun is a TLT device,
in following, and since UNUN was coined from balun, I would expect UNUN
to only apply to TLT devices. The device in the article is a simple RF
Transformer ... I like UN-UN, and the logic of following the naming
convention of the Bal-Un is followed, making it "intuitive."

Many similar articles about -
and adverts for - these devices WILL insist on calling them baluns
(which, of course, they are certainly not).

The direction of either winding on the torroid should not matter one bit.

The device here is not, IMHO, an UNUN, it is an RF Transformer, my first
post referred to it as such ... The winding direction, in regards to the
relationship of the direction of one winding to the other, matters a
great deal--indeed, since a 180 degree phase relationship is at stake,
the direction causes one to be an "opposite" of the other ... I have
always found the phase reversal winding direction(s) to exhibit superior
behaviors ...

Regards,
JS

--
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