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AM21N Questions

Discussion in 'DIRECTV HD DVR/Receiver Discussion' started by kevinturcotte, Feb 1, 2012.

  1. kevinturcotte

    kevinturcotte Active Member

    3,957
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    Dec 19, 2006
    Outside...
    Why can't they just make a super powerful omni-directional antenna? lol
     
  2. Davenlr

    Davenlr Geek til I die

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    Sep 16, 2006
    Physics :)
     
  3. kevinturcotte

    kevinturcotte Active Member

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    Dec 19, 2006
    Outside...
  4. Davenlr

    Davenlr Geek til I die

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    Sep 16, 2006
    Basically because they would cancel each other out, since there is no way to eliminate ALL the signal from coming in from the sides and back.

    Now, you COULD use the same type antenna used to TRANSMIT the signal at the TV station, but they are about 30-40' tall, and weigh several tons. They would, however, give you the gain you are wanting, and are onmidirectional :)
     
  5. kevinturcotte

    kevinturcotte Active Member

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    Dec 19, 2006
    Outside...
    Hmmm-wonder if my local NBC would notice if their's suddenly went missing? lol ;)
     
  6. bobnielsen

    bobnielsen Éminence grise

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    Bainbridge...
    They also have very narrow bandwidths, so you won't get many channels with one, even if you could afford it, cancelling out the advantages of it being omnidirectional.
     
  7. Davenlr

    Davenlr Geek til I die

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  8. kevinturcotte

    kevinturcotte Active Member

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    Dec 19, 2006
    Outside...
    And for about the same amount of money, I could probably also throw up one of those 1.8 meter Hawaii/Alaska Directv's dishes and pretty much eliminate rain fade lol
     
  9. TomCat

    TomCat Broadcast Engineer

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    Aug 31, 2002
    You sort of have to understand multipath to get this. Multipath is identical signals coming from different directions at different times; something 8VSB abhors. When a TV signal bounces off a watertower or building, the main signal arrives earlier than the reflected signal, and the bits all mix together, flummoxing the decoder. It would be like two people saying the exact same thing to you, but one is delayed by a second or two, which means you might not be able to understand either of them. The decoder doesn't know if the bits it sees coming in are arriving in the proper order or not, and if they are mixed with reflected signal it can't tell them apart, and so loses the ability to decode.

    The two solutions to multipath both rely on minimizing the reflected signals. Tuner technology does active EQ to find and suppress echoes, and antennae can be built to have directionality, meaning the signals reflecting from different directions will be suppressed.

    If you take multiple antennae that are directional and simply combine them, what you are doing in effect is creating an antenna array that has less directionality than either of the two antenna components, and that is exactly what you want to avoid.

    That is why combining antennae is always a compromise and must be done in very specific ways to be effective. There are ways to increase directivity by combining antennae in an array, spacing them a quarter wave-length apart, and pointing them all in the same direction. You also have to make the leads exactly the right length to get the signals to combine rather than cancel. But there is no way to pick up from different directions using multiple antennae without increasing the probability of more multipath interference.
     
  10. shalverson

    shalverson AllStar

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    Oct 27, 2003
    Hi,

    I have an AM21 tuner that I bought in 2008 that I used to have hooked up to my H20 series receiver. That had the option of searching for the over the air channels.

    Now I have an HR34-700, and an HR24-500 and I can't get either one of them to work with the AM21. How do you get it to search for the digital OTA channels? It just doesn't even recognize that I have it hooked up.

    Any help is appreciated.

    Thank you,

    Scott
     
  11. hasan

    hasan Well-Known Member

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    54
    Sep 22, 2006
    Ogden, IA
    Have the AM21 disconnected from the sat box. Do a menu restart on the sat box. When it powers completely down (the front panel lights will go off), pull the AC plug from the wall. Plug the AM21 back in as required. Plug the power back in on the sat box. Let it boot up.

    It should recognize that you have the AM21 connected at this point.

    Go into Menu > Setup > Antenna Setup and configure the OTA setup with your primary zip code, etc.

    You should be good to go after that.
     
  12. bobnielsen

    bobnielsen Éminence grise

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    Jun 29, 2006
    Bainbridge...
    The H20 had a built-in OTA tuner and did not use a AM21. Your current setup will not scan for channels but uses a database. Follow hasan's suggestions to get it going.
     
  13. shalverson

    shalverson AllStar

    71
    0
    Oct 27, 2003
    Great advice guys! Directions for hookup worked great!

    My old receiver I needed the AM21 on was either an HR20-700, or an HR21-100, can't remember for sure.

    Anyway, it works great now!

    Really appreciate the help with this!

    Scott
     

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