[Moon-Net] Question about polarization a noise. Odd behavior.
nlsa at nlsa.com
Sun Nov 20 00:18:43 CET 2016
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 at 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.
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