[Moon-Net] Question about polarization a noise. Odd behavior.

Dave Redman davidredmang4idr at gmail.com
Sun Nov 20 10:18:52 CET 2016


Bob,
If I understand your mail correctly you rotate the booms of the 2 yagis (
extract ;*The array is 2x28el and both booms rotate at the same rate in the
same direction and so stay in phase. *)

1) a yagi is never the same radiation pattern in E or H planes
2) assume your 2 yagis are correctly spaced for the Horizontal beam to give
your desire array pattern ( max gain or min side lobes or whatever you
choose )
3) When the yagi are rotated to vertical polarisation the yagi spacing will
be incorrect to some extent dependent upon the difference in E / H plane
patterns
4) At all other positions as you rotate from Horizontal to Vertical the
effective array spacing will increase , reach a max at 45 degrees and then
decrease ( simple triangle calculation ).......again this will affect your
array radiation pattern
5) if the 2 yagis are not feed with a good balanced feed arrangement and
in-phase ( coax inner to same side of the antenna feed and the same
electrical length from the divider ) ) then this too will affect the
radiation pattern.
6) is your cross support is horizontal and metal or partially metal ( if
metal it is ok for Vertical but not for Horizontal  )
7) is your mast above the rotator metal then it is ok for Horizontal but
not for vertical ( and on 2m it should be 50mm max diameter )
8) Is your cross boom at least 1m ( on 2m ) above the top of the rotator /
support head unit
9) I understand your yagis rotate 180 degrees ( again maybe incorrectly )
if the noise / pattern is different 0 and 180 degrees and / or 90 and 270
degrees the any of the above could be influencing the array.
10) Surely you only need to rotate 90 degrees max ?

If my understanding is incorrect then apologies but some of the comments
above still are relevant

Dave
G4IDR




On 19 November 2016 at 23:18, Michael Owen <nlsa at nlsa.com> wrote:

> Bob -
>
>
>
> Is there a chance that your feedlines or connectors are not quite tight?
> Does the feedline remain in the same orientation relative to the antennas
> as they change polarization or does it snake around?  Does the noise vary
> smoothly with polarization rotation or does it jump?
>
>
>
> W9IP
>
>
>
> *From:* moon-net-bounces at mailman.pe1itr.com [mailto:moon-net-bounces@
> mailman.pe1itr.com] *On Behalf Of *Bob Atkins
> *Sent:* Saturday, November 19, 2016 3:14 PM
> *To:* moon-net at mailman.pe1itr.com
> *Subject:* [Moon-Net] Question about polarization a noise. Odd behavior.
>
>
>
> I just got my polarization rotation running properly for the contest last
> night.  I observed two things, one I understand (?) and one I don't.
>
>
>
> I know I have a background noise issue on 432 (which isn't coming from my
> house). Last night I noticed that at one polarization (say horizontal) sky
> noise was about 3dB LESS than a 50 ohm load - as it should be. However at
> the orthogonal polarization (say vertical) "sky" noise was up to 3dB MORE
> than a 50 ohm load. So whatever is the source of my local noise, it's
> polarized and it's reducing my sensitivity by up to 6dB (despite which I
> made 16 QSOs last night).
>
>
>
> So far, so good (more or less...except for the noise)
>
>
>
> However, I also found in some cases that 180 degrees rotation CLOCKWISE
> from, say, horizontal to vertical (+180 degrees) gave a DIFFERENT noise
> level than a 180 degrees ANTI-CLOCKWISE rotation (-180 degrees), something
> that I'm not sure I understand. Both rotations go from, say, horizontal to
> vertical, but the end up 180 degrees out of phase. How can that affect the
> noise level?  Vertical polarization is vertical polarization right? The
> phase only matters when combining antennas. The array is 2x28el and both
> booms rotate at the same rate in the same direction and so stay in phase.
>
>
>
> What don't I understand here?  This excess noise is annoying and seriously
> limits weak signal work (unless the signals happen to be at the
> polarization that picks up least noise!). I'm still trying to figure out
> where it's coming from. Maybe this odd "phase" issue is giving me some sort
> of clue?
>
>
>
> If anyone has any thoughts on this, I'd appreciate hearing them.
>
>
>
> Bob
>
> KA1GT
>
> _______________________________________________
> Moon-Net posting and subscription instructions are at
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>
>
>
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