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Explain dithering

Discussion in 'DIRECTV Installation/MDU Discussion' started by peters4n6, Feb 19, 2008.

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  1. peters4n6

    peters4n6 Legend

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    Dithering (as per wikipedia):

    http://en.wikipedia.org/wiki/Dithering

    Sounds awfully mathematical and engineering-oid.

    At least when it comes to satellite aiming/calibration, I'm a newb. When I get my 5-LNB installed, will it be enough to say, "Don't forget to dither the thing," or will I need a bit more specialized knowledge to get the best alignment. Any advice would be appreciated. I did a search and failed to come up with anything except consensus that dithering is important.

    eric
     
  2. doctor j

    doctor j Hall Of Fame DBSTalk Club

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  3. SledDog

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  4. Tom Robertson

    Tom Robertson Lifetime Achiever DBSTalk Club

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    It can also be done with patience and the satellite meters built into a receiver.

    Cheers,
    Tom
     
  5. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    "Explain dithering" [as it pertains to dish alignment].
    When the 5 LNB dish first came out not every one had meters that could read the new SATs [Ka], so the goal was to center off the older Ku SATs, but Ku is a broader beam than the Ka beams. "Just" tuning to a strong level from Ku, could still be off center on the Ka.
    "Dithering" is to find the sides of the Ku beam, by fine tuning to a given level on each side of the beam and then finding the exact point in the middle [which the meter wouldn't show]. If you have the Ku set to the exact middle, then the narrower Ka "should be" aligned.
    Now that there are meters that read Ka and the software has been updated on the receivers, you can peak the dish off the Ka SATs using either.
    For your installation, simply make sure the 99/103 SATs have good levels too. How the installer does it doesn't really matter, as long as they do it [well].
     
  6. Mertzen

    Mertzen Hall Of Fame

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    Exactly. I don't need a fancy meter or the the 2 turns this way and all. If the mast is solid and plumb all one needs is common sense really.
     
  7. peters4n6

    peters4n6 Legend

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    thanks all. looks like I just need to double-check the readings off the receivers before the guy leaves to be safe.

    eric
     
  8. joe diamond

    joe diamond Hall Of Fame

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    When I explain it I try to use the word congruent last in the explanation. You set the mast plumb and secure. Then you set the tilt and elevation as close to the published specification as you can. Lower the dish & mounting head unit on to the mast and tighten until there is friction when the dish is rotated but not enough to bind. Point the dish along the line of the mast and the published azimuth. Check and recheck the signal until the 101 and 119 signals are equal. Give a little push east and tighten the rear bolts a little more. Check all the signals.

    Since the LNB is one piece any movement you make affecting one satellite tuning will cause an effect on all the others. This in the congruency thing.

    Then folks say you didn't touch the little dither things.

    Yup.........well nope; didn't mention it & didn't use em. Skillful poosh! Not too much, not too little......just right!

    Do fully tighten all the bolts evenly. The wind will rotate that sucker unless you crank hell out of the bolts..........don't break them, however.

    Joe
     
  9. TheRatPatrol

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    I thought you didn't need to "dither" with the new back assemblys, only with the older back assemblys, as shown in the videos?
     
  10. D-Bamatech

    D-Bamatech Godfather

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    Dither = Over complication & a used word for nothin'.

    No Need period & never has been.
     
  11. Mertzen

    Mertzen Hall Of Fame

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    Nah still need it. Only difference is a the amount of turns back and forth. 3 vs 2.
     
  12. TheRatPatrol

    TheRatPatrol Hall Of Fame

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    But in addition to the above, I also thought "dithering" was used BEFORE the new sats went up so that when they did go up the dish was already aligned? Now that the new sats are up and running, don't they use the sats to fine tune things?

    Sorry I guess I should have been more clearer in my original post.
     
  13. MrCastle

    MrCastle Cool Member

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    I dither if for no other reason than it couldnt hurt. I have run into situations where dithering was the only way to get a maxed signal. I have also run into situations where dithering was necessary after replacing the LNB.
     
  14. BattleZone

    BattleZone Hall Of Fame

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    Let's use a carpenter analogy.

    If you have a board that is 6' long exactly, and you want to find the exact center, you can just measure 3' and you're done. 6/2=3.

    But what if you have only a 25' measuring tape, and you need to find the exact center of a board of unknown length that is between 55' and 60' long? Your tape won't reach the center, so you can't get an accurate length. How to solve the problem?

    One solution is to measure 25' from each end, and mark the board. Now, the space between the two marks is measurable with your 25' tape, and you can easily measure the distance between the marks and divide by 2 to find the exact center of your board.

    That's what's going on with the sat alignment.

    The Ka signals have a very narrow beam that requires very precise alignment, but most meters only read Ku signals, which has a wide beam that does NOT require as precise of alignment. What this means is that a Ku meter will show strong signal over about 2 full degrees of movement, but the Ka signals require tuning to within half a degree.

    So, how do you find the center of the Ka signals when your meter won't read them? You use your meter to find the center of the Ku signals by finding how many turns left and right you have to turn the fine-tuning knobs to get the Ku signal to drop by, say, 20 db. Then, you split the difference, and you're perfectly centered.

    Another solution is to buy a second $600 meter that will read Ka signals, but given how underpaid most techs are, and how few even have a decent primary meter, you won't find many techs set up with, say, a Birdog AND a SatBuddyIII.
     
  15. MrCastle

    MrCastle Cool Member

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    Id like to add that two full degrees here on the ground equates to about 800 miles up there with Dtv's sats. that's why dithering is such a precise task.
     
  16. slimline

    slimline Legend

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    i use a acutrac 3 and i dont dither any more...

    i get the same results with the meter compared to completing the dither method.

    how ever if you dont have a meter that will read ka signals you must dither ..
     
  17. TheRatPatrol

    TheRatPatrol Hall Of Fame

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    Can you still use the receivers meters if you don't have a meter though?

    Thanks
     
  18. houskamp

    houskamp New Member

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    You'll want to be able to see the reciever meters but yes they will work.. slingbox/laptop is my favorite...
     
  19. GTS

    GTS Member

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    Hi All,
    Long story short,
    A) If you can monitor the Ka signal strength to perform the alignment, do so.
    B) If not possible to monitor the Ka signal, you must perform the dither alignment in order maximize signal strength for the new HD programming.

    IIP,
    That is one of the best non technical explanations I've heard. Good job.
     
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