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Re: Re polarity control box - again



  Hi Gus,

if you mean the FIG.68 in VHF/UHF manual (page 8.28),  I can't see something
wrong.
I have made this system a few years ago and I did not notice any problem.

Position 5 for RHCP has a Matching stub (L/4 75 Ohm) in series with 135'
Yagi and
a Matching stub (L/4 75 Ohm) + a Phasing-stub (L/4 50 Ohm) in series with
45' Yagi.

Position 6 for LHCP:  a Matching stub (L/4 75 Ohm) + a Phasing-stub (L/4 50
Ohm)
in series with 135' Yagi and  a Matching stub (L/4 75 Ohm) in series with
45' Yagi.

Where is the L/2 (as you pointed out) ???  I can't see it.

The 135' Yagi on LHCP is fed with 2 stubs in series,
but the first one is L/4 50 Ohms and acts as "Phasing stub" and the second
is L/4 75 Ohms "Matching stub".  They have different "Z"  each one, so
there are not 2 pieces L/4 50 Ohms = L/2 50 Ohms.


73, Mak SV1BSX



----- Original Message ----- 
From: "Angus" <angus@young5769.freeserve.co.uk>
To: <amsat-bb@amsat.org>
Sent: Wednesday, August 06, 2008 6:06 PM
Subject: [amsat-bb] Re polarity control box - again


> Hi all, its me again, sorry.
> OK got the 2mtr polarity control box working and very pleased, except for
> one very small item.
> LHCP never seemed to me to be 90 degrees out of phase with RHCP, never had
> the large drop in signal I expected.
> OK time for a bit or research and looked in to my VHF/UHF manual and found
> the pages and guess what, the design we have been using is wrong, or so I
> think, please correct me if I am wrong.
> OK both yagis have a 1/4 wave 75 ohm matching system to allow the system
> back to work with 2 x 50 ohm yagis in parallel, in case anyone forgets, so
> for Vertical both yagis fed in phase, for Horizontal the 135 degrees yagi
> is fed with a 1/2 wave of 50 ohm line to delay it by 180 degrees, no
> problems so far.
> For RHCP the 45 degrees yagi is fed with a 1/4 wavelength of 50 ohm  delay
> line and again no problems.
> NOW HERE'S THE RUB!
> For LHCP we feed the 135 degrees yagi with a 1/4 wavelength of 50 ohm
> line, woops the system has a 1/2 wavelength of 50 ohm line!
> So instead of feeding as we should we are feeding it to make it simpler
> than it should be. Hence I was never happy that LHCP was never quite 90
> degrees out with RHCP.
> So quite possibly we are going to get some form of strange oval type of
> polarity anyone take a guess at its true nature, I may have a play around
> with one of the antenna programs and see what comes out.
> Am I wrong completely on this or is it the better to have it off a little
> on LHCP to get the other 3 polarities correct?
> Sorry for boring some of you.
> regards
> Gus M0IKB
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