Jump to content


Welcome to DBSTalk


Sign In 

Create Account
Welcome to DBSTalk. Our community covers all aspects of video delivery solutions including: Direct Broadcast Satellite (DBS), Cable Television, and Internet Protocol Television (IPTV). We also have forums to discuss popular television programs, home theater equipment, and internet streaming service providers. Members of our community include experts who can help you solve technical problems, industry professionals, company representatives, and novices who are here to learn.

Like most online communities you must register to view or post in our community. Sign-up is a free and simple process that requires minimal information. Be a part of our community by signing in or creating an account. The Digital Bit Stream starts here!
  • Reply to existing topics or start a discussion of your own
  • Subscribe to topics and forums and get email updates
  • Send private personal messages (PM) to other forum members
  • Customize your profile page and make new friends
 
Guest Message by DevFuse

Photo
- - - - -

HR20 OTA - The Other Side of the Story


  • This topic is locked This topic is locked
56 replies to this topic

#51 OFFLINE   tkrandall

tkrandall

    Hall Of Fame

  • Registered
  • 1,795 posts
Joined: Oct 03, 2003

Posted 30 July 2007 - 03:30 PM

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


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

#52 OFFLINE   Meklos

Meklos

    Legend in his own mind...

  • Registered
  • 324 posts
Joined: Nov 07, 2006

Posted 30 July 2007 - 03:32 PM

So are you saying that replacing the antenna with one that is more tolerant of multi-path signals is in order?


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.

#53 OFFLINE   hasan

hasan

    Hall Of Fame

  • Topic Starter
  • Registered
  • 5,920 posts
  • LocationOgden, IA
Joined: Sep 22, 2006

Posted 30 July 2007 - 03:49 PM

So are you saying that replacing the antenna with one that is more tolerant of multi-path signals is in order?


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.
...hasan, N0AN

SlimLine5-SWiMLNB/DECA/WHDVR
HR44-700, WD20EURX 2 TB eSATA/ThermalTake Max 5 Enclosure

HR24-200, WD20EVDS 2 TB eSATA/ThermalTake Dock
HR24-200, H21-200. Samsung UN60C6400 60" LED/LCD
DirecTV since 1995

#54 OFFLINE   judson_west

judson_west

    Godfather

  • Registered
  • 257 posts
Joined: Jun 15, 2006

Posted 30 July 2007 - 03:49 PM

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.
Video/Audio 1: DirecTV HR24-500 (HDMI)-> Sony STR-DA5200ES -> Sony KDL-52XBR9
Video/Audio 2: DirecTV HR20-700 (HDMI) -> Sony KDL-32EX500
Video/Audio 3: DirecTV HR20-700 (HDMI) -> Sony KDL-40EX500

#55 OFFLINE   hasan

hasan

    Hall Of Fame

  • Topic Starter
  • Registered
  • 5,920 posts
  • LocationOgden, IA
Joined: Sep 22, 2006

Posted 30 July 2007 - 04:06 PM

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.


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)
...hasan, N0AN

SlimLine5-SWiMLNB/DECA/WHDVR
HR44-700, WD20EURX 2 TB eSATA/ThermalTake Max 5 Enclosure

HR24-200, WD20EVDS 2 TB eSATA/ThermalTake Dock
HR24-200, H21-200. Samsung UN60C6400 60" LED/LCD
DirecTV since 1995

#56 OFFLINE   Meklos

Meklos

    Legend in his own mind...

  • Registered
  • 324 posts
Joined: Nov 07, 2006

Posted 30 July 2007 - 06:29 PM

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)


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>

#57 OFFLINE   hasan

hasan

    Hall Of Fame

  • Topic Starter
  • Registered
  • 5,920 posts
  • LocationOgden, IA
Joined: Sep 22, 2006

Posted 30 July 2007 - 06:30 PM

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!
...hasan, N0AN

SlimLine5-SWiMLNB/DECA/WHDVR
HR44-700, WD20EURX 2 TB eSATA/ThermalTake Max 5 Enclosure

HR24-200, WD20EVDS 2 TB eSATA/ThermalTake Dock
HR24-200, H21-200. Samsung UN60C6400 60" LED/LCD
DirecTV since 1995




Protected By... spam firewall...And...