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@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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