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HR20 OTA - The Other Side of the Story

Discussion in 'DIRECTV HD DVR/Receiver Discussion' started by hasan, Jul 23, 2007.

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  1. Fish Man

    Fish Man Godfather

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    No, but the ATSC tuner in the HR20 relies on a "replacement" PSIP data, if you will, to determine channel mapping. It gets that data from the satellite stream.

    In other words, if UHF frequency 24 in "Anytown USA" contains digital channels 2-1, 2-2, and 2-3, a "normal" ATSC tuner scans the band and finds a modulated carrier on UHF frequency 24, it then picks up the PSIP data from that signal to determine what channels are on it and what to call them, e.g. "2-1 WPIG-DT" and "2-2 WPIG-24/7 weather" etc., as well as some other information about these channels.

    By contrast, the tuner in the HR20 gets this channel mapping information from the satellite stream.

    DirecTV gets it from Tribune (the same company from which they get their guide data), Tribune gets it from God-only-knows-where (but ultimately, it must come from the station itself, at some point).

    The "chain of information" in this case is fragile. Lots of chances for human error to screw up the data.

    Having a manual scan capability on the HR20 could "fix" problems introduced by human error. As I said before, the HR10 has such a manual scan function. Others have reported that the H10 and H20 do as well.
     
  2. tkrandall

    tkrandall Hall Of Fame

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    I suspect the reason D* went this way is they want the guide info for the local channel provided by them via satellite to agree exactly with the guide data the viewer see for his OTA channel. My guess at least.

    So, do normal ATSC tuners scan all known local channels "behind the scenes" so as to keep the guide current, whether you have tuned any particular station recently or not? I am getting the impression from this discussion that is the case, but it has not been explicitly stated.
     
  3. mpotratz

    mpotratz New Member

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    Jul 21, 2007
    Ah, but it does. All of our program guide data is encapsulated in the PSIP stream along with everything else. That is exactly where an ATSC HD receiver gets it. D* doesn't use it even though it's there!
     
  4. mpotratz

    mpotratz New Member

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    Jul 21, 2007
    Our PSIP data is constantly being feed in our signal to any ATSC HD receiver that can receive it. When we get updated program guide information, it is automatically inserted into the PSIP stream which then goes out.

    I can't say 'explicity' that is constantly scans behind the scene, or it just updates when you hit the GUIDE button on your remote. But, either way, the receiver is always being fed the latest information.
     
  5. judson_west

    judson_west Godfather

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    Jun 15, 2006
    My situation is a little different whereby I get good signal strength from all of my HR20's OTA signals, but I can't get consistant reception of most of the stations. My TV that is connected to the same ANT cable (split between the HR20 and the TV) has no trouble getting any of the stations at any time. How do I know if this is a tuner issue or an antenna (multipath) issue?
     
  6. JMCecil

    JMCecil Godfather

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    Jan 20, 2007
    This is a great question. I lose CBS constantly on the HR20, but it has a 90+ meter reading whenever I check it. It never blips if I watch on my TVs tuner.
     
  7. Meklos

    Meklos Legend in his own mind...

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    Probably a multipath issue... Also remember, the meter reading (IIRC) is a bit-error-rate reading, not a raw signal power reading.
     
  8. tkrandall

    tkrandall Hall Of Fame

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    The meter reading on the HR20 specifically, or meters in general?
     
  9. Meklos

    Meklos Legend in his own mind...

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    OTA ATSC signal readings in general. Don't know on the sat side...
     
  10. judson_west

    judson_west Godfather

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    Jun 15, 2006
    So are you saying that replacing the antenna with one that is more tolerant of multi-path signals is in order?
     
  11. tkrandall

    tkrandall Hall Of Fame

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    Is that specified somewhere in the ATSC documents? I'd love to have a better understanding of my various OTA signal strength readings.
     
  12. Meklos

    Meklos Legend in his own mind...

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    I don't know if there's any electronic magic that can happen inside the antenna to reduce multipath. From a physical design perspective you could have an antenna that had a very tight 'beam width' so that it only 'saw' signals in a very small window (like looking down the tube of a roll of wrapping paper), and that might help if you're getting off-axis multipath...

    But normally I think multipath rejection is a function of the OTA tuner itself.
     
  13. hasan

    hasan Well-Known Member

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    Ogden, IA
    Yes, but I would word it more correctly so we don't confuse people: you want an antenna that is highly directional, thus discriminating AGAINST multi-path, not being more tolerant of multi-path. The idea is to exclude the 2nd or 3rd or 4th signal source, and the way to do that is with an antenna that has a highly directive (narrow) forward lobe and a decent front to rear rejection (called ratio).

    Antennas have two important characteristics: gain and directivity. They do NOT correspond completely. Some people think that the antenna with the higher gain automatically has better directivity, but this is not always the case. It is true in general, but there are some very significant exceptions.

    You want the narrowest and cleanest (absence of significant sidelobes) pattern you can get out of an antenna. You have to check each antenna model and it's pattern to be sure you are getting what you need. There are a lot of very good antennas out there that have reasonable gain and decent directivity....you just want to make sure that is what you get. For multi-path, gain in and of itself is unimportant, while DIRECTIVITY is whole ball game.

    Assuming the guide info is right in the HR20 (and it's not telling the HR20 to tune to the wrong frequency or wrong channel), if you are seeing strength in the 90's or even down to the high 50's and cannot get a reliable picture, you most likely have multi-path and need a more directive antenna.
     
  14. judson_west

    judson_west Godfather

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    The antenna I currently, that works fine for my TV, is a medium directional. According to antennaweb.org, a medium directional is in order to receive most of the digital channels. I guess the problem is with the tuner. POOP.
     
  15. hasan

    hasan Well-Known Member

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    Ogden, IA
    No, normally, the it's the antenna's job to provide the cleanest signal possible to the tuner...it's only through the miracle of modern engineering that some tuners exhibit a certain amount of tolerance for multi-path. Fix it out front, not after cow's left the barn.

    You had it right the first time....high directivity makes up for the sins of an inadequate tuner. It can be solved externally....with a highly directive antenna. See my other post. Since the OP can't change the tuner, he needs to change the antenna...there are no other choices. Fortunately, multi-path is pretty easily solved (except in the most severe environments) with a narrow and "clean" antenna. I say clean, because simply having a very tight primary beam width is not enough...if there are sidelobes that are only a few dB down from the main lobe, you will still get multi-path. Many a fine antenna has been ruined by poor design, paying attention only to the tightness of the main lobe and ignoring the problems caused by sidelobes, and/or a very poor front to rear ratio.

    p.s. nearly all multi-path is off-axis. on axis multi-path is very, very rare...but it can happen...and then the strength of the tuner is the only solution, short of selling your house. (not really true, you could elevate/de-elevate the antenna and make progress against on-axis multi-path)
     
  16. Meklos

    Meklos Legend in his own mind...

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    For some reason, I had it in my mind that certain tuners were better at detecting the proper phase for the incoming primary signal and somehow sampling and phase-inverting the 'offending' reflections.

    Only place I've seen on-axis multipath is two places. One, a reflection from the city when the transmitter was directly between the city and the viewer. Second, people up on the ridges north of Nashville can get on-axis multipath, and I'm not sure if it's groundbounce or cloudbounce / tropo / something similar, but it's the only thing I can think of.

    Nothing like getting an on-axis .75 sec multipath echo on 3.8MHz... <eg>
     
  17. hasan

    hasan Well-Known Member

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    Some are, but it's better to fix it before it gets to the tuner and YES!, you have given the example of the worst kind of multi-path. Nice job!
     
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