[TowerTalk] Baluns...again.

[Stan Stockton]

Pawsey Stub.  Go to G0KSC's nice website.

http://www.g0ksc.co.uk/creatingabalun.html

Stan, K5GO


Sent from Stan's IPhone



On Dec 28, 2010, at 9:04 AM, "Jim Thomson" <jim.thom at telus.net> wrote:

> 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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