Diddy1
join:2003-07-19
Sidney, NE
| reply to LLigetfa
Re: Flat Panel vs. Grid
said by LLigetfa  : My guess is the panel is more polarity agnostic while the grid needs to be more precise. I heard that a few degrees off on rotation can really drop off on a grid. When a sector is down-tilted, the further out from centre you go, the greater the polarity rotational skew. Can you elaborate on these to thoughts? I'm thinking when I mount a mast or DSS arm for client antenna, I may be off slightly on polarity. I just eye-balled it. Does anyone actually take steps to ensure plumbness?
Aarom
Aaron |
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robbin
Premium,MVM
join:2000-09-21
Leander, TX | I always use a small level to insure that the mount is plumb and level. Then if I want it out of plumb I make the necessary adjustments. |
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Diddy1
join:2003-07-19
Sidney, NE | But, we should always start with a plumb mount, would you agree?
Aaron |
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LLigetfa
join:2006-05-15
Fort Frances, ON
| reply to Diddy1
A dish is very much affected by slight polarity skews. If ever you worked with satellite dishes, you would have come across this. The dish normally has only a single element up in the feedhorn and the signal is literally focused on it.
Panel antennas on the other hand are designed with multiple elements arrayed in such a way as to interact with one another. They are generally also designed to accept signals with skewed polarity as one may expect from multipath.
Downtilt on a sectoral is not uniform along its full beam width. Take as an example an old 33 1/3 LP record player with stacking spindle and put one record up on the stacking part. Now, tilt the record so that the edge touches the platter and you will notice that 90 degrees to either side, there is no down tilt. There is however, polarity skew. Now I realize that this is quite an exaggeration and that in reality, the downtilt on a sectoral would normally be less than 5 degrees, but if one is sloppy in not plumbing the masts on both ends, the errors can compound. The mast should always be plumb and adjustments made to the mount. |
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Diddy1
join:2003-07-19
Sidney, NE
| Ok, I think I understand what your getting at. So what your saying is that to either side of the sector, the polarity is being tilted as well.
However, the client we did the test with, is visually in line with the center of the sector. The sector has little down tilt and I've tried in the past to tilt a little more with bad results so we put it back where it was. The tilt, if I go by the gauge printed on the bracket itself, is 1*.
Aaron |
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