[Moon-Net] Question about polarization a noise. Odd behavior.
davidredmang4idr at gmail.com
Sun Nov 20 10:18:52 CET 2016
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
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
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
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
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?
> *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.
> Moon-Net posting and subscription instructions are at
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