From: Máximo EA1DDO_HK1H
Sent: Monday, August 29, 2011 8:03 AM
To: towertalk@contesting.com
Cc: jim.thom@telus.net
Subject: Baluns...again
Hi Jim,
You wrote;
"Apparently there was an article out about doing just that. The ant was a
quad...
I have not seen the article, but it was brought to my attention by a local ham."
I would like to read that article.Do you know where can I found it?or, Who
wrote it?or perhaps you know the "local ham" who I can ask to.Thank you very
much.73, Maximo - EA1DDO/HK1H### gary, VA7YO read it in a ham magazine a few
yrs ago, don't remember which one. I saw some flack about it as most hams will
confuse it with an electrical 1/4 wave transformer, likeusing 75 ohm coax to
match 50 ohms to 100 ohms etc. In this case. either a PHYSICAL 1/4 wave OR
3/4 wave of50 ohm coax is used between top of tower and the 50 ohm DE of the
yagi or 50 ohm DE of the quad. Shield wasbonded to top of tower. The actual
length of 50 ohm coax used was 2% shorter than the physical 1/4 or 3/4 wave.
End result was a sky high Z at the DE feed-point. I used a combo of large
type 43 beads slid over RG-393 Teflon coax at theDE and also a 1/4 wave of
coax. A remote switch box is used, and mounted to just above top of tower on
the mast. I could onlyuse the phy 1/4 wave - 2% on the upper bands... like
17+15 M . Nothing blows up or overheats with real high power. The
trickhinges on the phys 1/4 wave - 2%.....and not an electrical 1/4 wave. We
are not trying to transform Z's. later... Jim VE7RF
_______________________________________________
To: <towertalk@contesting.com>
Subject: [TowerTalk] Baluns...again.
From: "Jim Thomson" <jim.thom@telus.net>
Date: Tue, 28 Dec 2010 07:04:13 -0800
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
Looking through some old notes plus the info on Jim Brown's site.... there
was a question about using
an electrical 1/4 wave or electrical 3/4 wave of coax. The 1/4 [3/4]
wave of coax was run between the
DE of the yagi and the tower... with the braid of the coax bonded to the top
of the tower.
The theory is... if a 1/4 [3/4] wave of coax has it's braid bonded to the
top of the tower... the Z at the DE
should be sky high..and there should be no requirement for a balun.
Apparently there was an article out
about doing just that. The ant was a quad... and individual 1/4 wave [ and 3/4
wave] pieces of 50 ohm coax
were brought to a remote switch box at the top of the tower..where of course
all the braids are bonded to the tower
top. The author claimed that no baluns were needed on the various loops used
on each band. I have not seen the article,
but it was brought to my attention by a local ham.
W8JI also mentioned the use of 1/4 and 3/4 wave lines from DE to tower
top...and bonding the braids to tower top. Seems
to me that W8JI mentioned that if a balun was used in conjunction with the
1/4 [3/4] wave coax, that the balun would makes things
worse. There was some discussion on one of the other refelctor's years ago
about the 1/4 and 3/4 wave concept. It had something do do
with the height of the tower. If the tower was not the 'correct height'....
the concept would not work. Does anybody remember this ?
In one of Jim browns write ups.... there is a depiction showing feedlines of
various lengths... from 0 up to... but not quite 1/4 wave. Then
the chart starts up again... just a bit longer than a 1/4 wave..... and up
to... but not quite a 3/4 wave. Then it starts up again.. just past a 3/4
wave. OK, what gives? Is an electrical 1/4 wave and odd quarter waves
the real answer to a high Z on one band ? In the case of
something like monoband yagis.... this may prove to be a huge benefit... if
the theory actually works. If I remember correctly, the main coax
braid was bonded to the base of the tower as well. IF the theory does work...
and a high Z is presented to the DE... how high is this Z? Is is
mainly reactive... mainly resistive..or a bit of both ? Why would a bead
balun or torroid balun, when used in conjuntion with a odd qtr wave
of coax makes things worse ?
later........ Jim VE7RF
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