127w strange skew on horizontal TPs

Cham

Cham

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VE4GLS
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Dec 19, 2008
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Noticed I had to change the horizontal skew by about 20 degrees a couple days ago to get some of the channels on 127. Vertical seems to have changed slightly too but not as bad, maybe 5 deg. Of course using a C2W-PLL LNBF the vertical TPs did drop in signal a bit.
Yesterday the signals were weak once again, had adjust the horizontal skew another 5 degrees, vertical TPs dropped in signal another dB after the adjustment.
Feedhorn is well clamped in the scaler so it shouldn't be turning, and the dish is mounted solid (it can't turn unless by loosening mounting hardware).
Looked inside, seems dry with no obvious snow or ice.
Also this is on an 8ft offset dish. Temps have been down in the 0F at night maybe a touch below. Warmed up overnight here though almost thawing now. Signals this am the same as yesterday (so far).

Is anyone else seeing this (maybe a satellite's antenna issue) or maybe I have a weird problem with my LNBF...? Maybe the H antenna probe is wandering around inside feedhorn... :|
 
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Titanium

Titanium

AI6US
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May 23, 2013
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Possible adjacent satellite or cross polarity interference is being attenuated by the additional skew or feed adjustment. Correct FD setting to null sidelobes? Perfect parabola?

Expect more adjacent satellite interaction using minimum diameter reflectors. Each satellite will be packing both polarities with higher FEC muxes within the reduced bandwidth. Satellites used to be able coordinate frequency and polarity usage with neighboring satellites to minimize interaction across a wider available spectrum. Now they will need to reuse available bandwidth to maximize the available space.

More important than ever to not only have the largest reflector possible, but to assure an efficient patabola surface and correct feed / scalar placement.
 
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Cham

Cham

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VE4GLS
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Dec 19, 2008
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Hi Brian,
This is actually a Ku dish so the surface for C-band should be good, no dents or anything, was real careful getting it home from the original site.
Seems to have been stable last couple of days now. Quite possible another TP on the same frequency or close by on an adjacent satellite could potentially cause that, but nothing new has shown up on scans (using a different dish).
Since this is a Ku dish I carefully measured the position of the orignal BUC/Feedhorn set set the C-band scaler/feed horn accordingly. Found the feed horn best position to be about a 1/2" closer to the reflector, and set the scaler to max out the signals up and down the band on both polarities (or best result on the TPs I am interested in), so it may not be exactly in the perfect position to attenuate all the side-lobes.
I'll leave it where it is for now, if things change again I'll have to re-visit the scaler/feed position. Just strange how that particular satellite signal polarity changed within a few days. If anyone else noted a change then it might be a satellite issue. If not it would be at the receiving antenna, I suspect we've isolated the issue to the latter.
Cheers!
 

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