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

Bob Atkins ka1gt at hotmail.com
Sat Nov 19 21:13:30 CET 2016


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
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