Does changing the skew on a DishPro 500 change the look angle?

[kanjaji]

I am in an area that has heavy tree coverage . . . but there are "holes" that could work.

Here's my question. When I point the DishPro 500 to the suggested azimuth and then adjust the skew (by an off-axis rotation of the dish, not the LNBF) does this change the actual "looking angle" as it appears to do? For example, if the suggested azimuth is 236 with a dish skew setting of 135 (Dish's metric, not the true skew angle), the perpendicular angle from the front of the dish appears to change to a different azimuth than at 0 skew. Obviously, this makes a difference as I would have to find the "hole" for the new "true" azimuth (where the dish is actually looking).

My geometry may be off but it appears to me that because the dish is skewed from a point not in the center of the dish then the azimuth angle has to change somewhat with the skew. If this is true, how do I compute this new azimuth?

 

[garys]

The skew is so one dish can hit two or more sats in a row. If you are trying to hit one sat only, set skew to 0. Two or more, the skew would have to be set for your area (according to what you posted 135). If you change it you will have a hard time getting signals from all sats you are aiming at. The numbers are designed as a starting point, but there isn't much leeway.

 

[boba]

You may need two dishes to find 119 & 110 through holes in foliage. If your foliage is really that bad you would probably be better off finding an alternate programming source. Next year the foliage is going to be different from this years, trees continue to grow each month.

 

[Smith P.]

From geometry stand point: your dish far far away from satellites ~22600 miles, now imaging where are you and how significant your vobulation if changing skew.

 

[kanjaji]

Thank you all for your comments. I understand the basics of set up and the need to follow the Dish settings but they are designed as nominal settings (I think). I believe that the skew adjustment changes the looking azimuth by an unknown (to me) amount and thus need to determine what the actual change in looking azimuth is for a given amount of skew change if my assumptions about the geometry are correct. I may be overanalyzing this. Since the actual computed azimuth from my location is 243 (for 119) and 233 (for 110) perhaps the answer for me is to simply make sure that I have a clear sight window from about 228 to 248 and that should give me the leeway for a good hit.

 

[tnsprin]

Thank you all for your comments. I understand the basics of set up and the need to follow the Dish settings but they are designed as nominal settings (I think). I believe that the skew adjustment changes the looking azimuth by an unknown (to me) amount and thus need to determine what the actual change in looking azimuth is for a given amount of skew change if my assumptions about the geometry are correct. I may be overanalyzing this. Since the actual computed azimuth from my location is 243 (for 119) and 233 (for 110) perhaps the answer for me is to simply make sure that I have a clear sight window from about 228 to 248 and that should give me the leeway for a good hit.

The skew is the one thing you don't want to play around with. It pretty much is set it as specified for your location if aiming at multiple satellites. And set to 90 and aim the other as if a 300 for a single satellite (don't use the 500 values).

(corrected as per Iceberg's post)

 

[Mr Tony]

if you are aiming at a single satellite, skew is 90 (not 0). 0 would be up and down

 

[SmityWhity]

Well, Simple Simon said to me, "a little knowledge is dangerous", and the only thing I can say is, "a mind is a terrible thing to waste" so here's 2 of my senses.

As others have already said -- Enter the zip code for a Dish 500 and you will get the skew, elevation, and the azimuth as magnetic (and maybe it's updated with the annual magnetic deviation).

90 and 0 degrees skew: The Dish 500 skew set to 90 technically = 0 degrees, i.e., neither a + nor a - offset.

The Dish receiver calculations will actually give you the azimuth for your location for a single bird at 114.5W (half way between 110 and 119). Likewise, the skew is the happy middle between the 2 birds as calculated from various programs. But setting the skew to 90 (0 degrees) when using a single LNBF on a I-Bracket to receive a single satellite should give you an excellent signal after adjusting the elevation and azimuth. For such a single satellite dish, you could change the skew as provided by various programs, but will have to adjust the azimuth and elevation. This could be helpful with a limited view and not much room to relocate a dish, but moving the family or changing program source may be better alternatives.

So to answer your question,
"When I point the DishPro 500 to the suggested azimuth and then adjust the skew (by an off-axis rotation of the dish, not the LNBF) does this change the actual "looking angle" as it appears to do?
Yes it does.

So in response to your comment,
"I believe that the skew adjustment changes the looking azimuth by an unknown (to me) amount and thus need to determine what the actual change in looking azimuth is for a given amount of skew change if my assumptions about the geometry are correct."
Although I feel your assumptions are correct, I don't believe doing so is your solution. I believe if you make any significant changes to the skew, and then compensate/correct the angles by adjusting the azimuth and/or elevation, you will effectively be changing the arch for the locations you are looking at, instead of looking at the normal arch of the satellite (Clark's) belt. In other words, if you get 1 bird, you will be looking for the 2nd bird either below or above the belt.

Although it sounds like you are going to use the correct settings and look for the best opening, maybe the above will help if you decide to experiment.

Good luck.

NOTE: I never took geometry and slept through the Louisiana math classes while in high school (but got a 100 on every weekly test).

Multiple wrongs often equal a right.

 

[SimpleSimon]

Good job SmityWhity! You've got it down pat!

In short, set the skew per the book or receiver (making sure it's right - there's known errors in the D1000 book).

Make sure you've got clear view for 5 degrees azimuth each side of "center" (it doesn't need that much, but compasses and eyeballs are rarely perfect. You want to see a tight one - hit the "View my equipment" link just above and check out my 61.5 LOS.

Don't worry about the fact that the LNB arm is skewed - when you go to aim it, you'll just swing it back and forth until you've got correct signal.

THEN look at where the arm is "pointing" and scratch your head, cause "that just can't be right".

 

[mbarnes]

A late reply to this thread, but I don't get in here often, especially since I have been moving over the last month.

Anyhow, skew is technically defined as a variation from the nominal. It was originally applied to vertical and horizontal polarization formats. As you deviated from a due south look angle, the polarity also deviated from true vertical or horizontal by the skew angle. Since the skew adjustment can be critical, it is an awkward alignment to make for the typical consumer. Circular polarization of the signal effectively eliminates the need for skew adjustments. That made things fine for the DBS business initially, but then the need to point at multiple satellites came into play as content increased. Now, once again, skew comes into play, but for alignment purposes, not for polarity issues. As mentioned in previous posts, the look angle for a multiple LNB setup will be adjusted to a point between the two targets. However, to keep the LNB in the focal point of the dish, the dish orientation must be changed from the nominal, or skewed to a point which places the LNBs at an appropriate point above or below dish angle referenced horizontal so they are properly focused referenced to the spacecraft location. This angle will vary with respect to the dish's location east or west of the actual satellite longitude.

All this actually only means that in this case, the skew does NOT reference 0 OR 90 degrees. The skew refers to a difference from the nominal horizontal reference across the dish if it were pointed normally at a single spacecraft.

I hope that makes some sense.