worlddirect elliptical dish: skew or not to skew?

[FTAer0024]

Greetings.. I've acquired a 20x36 directtv worlddirect elliptical dish last week. It seems to require more precise alignment than my larger BJU dish, but it performs just as well, from what I can tell (I tested it with the 30W sat, and the 97W.) The dish mount allows it to be skewed around its axis like you would normally skew an LNB. My question is, should the dish be skewed, or left horizontal? I have already replaced the LNBF it came with, with a standard linear one, and the reception is great with the LNBF skewed and the dish not skewed, but I wonder if the quality would improve even more if I skew the dish, too? I ran out of time and didn't experiement with that. What's the theory on that? It's on a fixed mount.. Thanks.

 

[KE4EST]

I find I get a better signal on a super dish I have, if I skew the dish. I would find a weaker transponder and see what you get with the LNB skewed as opposed to the dish skewed.

 

[Mr Tony]

If you can skew the dish by all means do that

 

[Wescopc]

If you skew the dish - it helps with adjacent satellite interference.
Bob

 

[Anole]

I've acquired a 20x36 directtv worlddirect elliptical dish last week....
I have already replaced the LNBF it came with, with a standard linear one, and the reception is great with the LNBF skewed and the dish not skewed, but I wonder if the quality would improve even more if I skew the dish, too?
What's the theory on that?

Here's the theory:

With an eliptical dish, you have a matching feedhorn on the LNB which looks at the entire surface of the wide/squat dish, and no where else.
So, with matching feed, you should skew the dish.

Putting on a regular round feed LNBF really gives away any performance you might have had.
I think that LNBF will "see" above and below your dish, and pick up extra noise.
Yes, you should still skew the dish, but even so, you've thrown away the advantage you started with.

 

[FTAer0024]

Anole and all, thank you for your replies. Here's what I did.. below, I am not trying to prove or disprove anything, this is just what I have experienced with this dish so far. I am sure my amateur testing techniques are full of inaccuracies but I thought I would share this experience anyway.

I decided to use the 30w sat, to test the skewing part. I tuned in to the weakest transponder, peaked the signal by adjusting the dish, then took a reading of quality, then skewed the dish ccw by the recommended 53 degrees for the 30w sat and set the LNB (esx521) skew to zero. Re-pointed the dish.. had to raise it by 2 degrees and move to the west a little.. peaked for the max signal on the same transponder.. got around 2-3 pts increase in quality, judging by my open box s9 signal meter.. my conclusion was, in quality alone, there was no significant gain achieved by skewing the dish.

Next, I replaced esx521 with its original, vertical oval shaped eagle aspen Ku linear DTV lnbf. Had to use some additional inserts inside the collar, to hold its skinny neck in place. Peaked for the max signal by moving the neck in and out. LNBF Skew was set to zero degrees. Ran through all the channels on the 30W. On some channels, Q was on par with ESX521. On other channels, it was lower. Q seemed to be lower on horizontal transponders, and higher on the vertical ones.. my conclusion was that the round feed LNBF did better in this test. Again, this is just my observations, and does not go against the matching feed shape theory, since I am sure, these two LNBF have different specs.. 'maybe', better electronics in ESX521 compensated for not fully optimal (for this dish) feed shape.

Judging by picture quality, ESX521 looked slightly better than the directv LNBF up-close, and standing about 6 feet away from a 30" LCD, I couldn't tell any difference in picture quality at all on non-HD channels.

Here's the theory:

With an eliptical dish, you have a matching feedhorn on the LNB which looks at the entire surface of the wide/squat dish, and no where else.
So, with matching feed, you should skew the dish.

Putting on a regular round feed LNBF really gives away any performance you might have had.
I think that LNBF will "see" above and below your dish, and pick up extra noise.
Yes, you should still skew the dish, but even so, you've thrown away the advantage you started with.

 

[BiggRedd]

Skew it. An installer friend gave me a brand new one they found in their warehouse, works great after I put a aftermarket LNB bracket and a standard LNB on it. It's the metric nuts and bolts that I didn't care for, had to buy a new set of sockets and wrenches....

 

[FTAer0024]

I left it skewed. It's a great performing dish, considering its compact size. I googled it some more, and it is noted as 24x36. Makes me wonder if mine is a 'first generation' (20x36)

Skew it. An installer friend gave me a brand new one they found in their warehouse, works great after I put a aftermarket LNB bracket and a standard LNB on it. It's the metric nuts and bolts that I didn't care for, had to buy a new set of sockets and wrenches....