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Re: [TowerTalk] Baluns...again

To: Máximo EA1DDO_HK1H <>, <>
Subject: Re: [TowerTalk] Baluns...again
From: "Jim Thomson" <>
Date: Tue, 30 Aug 2011 07:37:39 -0700
List-post: <">>

From: Máximo EA1DDO_HK1H 
Sent: Monday, August 29, 2011 8:03 AM
Subject: Baluns...again

Hi Jim,

You wrote;
"Apparently there was an article out about doing just that. The ant was a 
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:  <> 
      Subject:  [TowerTalk] Baluns...again. 
      From:  "Jim Thomson" <> 
      Date:  Tue, 28 Dec 2010 07:04:13 -0800 
      List-post:  <">> 

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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