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
- - - - -

Does AM21 only receive OTA channels?


  • Please log in to reply
24 replies to this topic

#1 OFFLINE   MRM

MRM

    AllStar

  • Registered
  • 96 posts
Joined: Sep 10, 2008

Posted 05 October 2012 - 01:29 PM

I tried searching for this and didn't come across anything. I am wondering if the AM21 will only receive OTA channels. Will it receive limited cable channels or not? I figure the answer is no, but I thought I'd ask anyway. Sadly, cable offers better PQ on locals than DirecTV does even when going through the AR21.

Edited by MRM, 05 October 2012 - 01:59 PM.


...Ads Help To Support This SIte...

#2 OFFLINE   dettxw

dettxw

    MRVing

  • DBSTalk Club
  • 4,049 posts
  • LocationChoctaw, OK
Joined: Nov 21, 2007

Posted 05 October 2012 - 01:38 PM

I think that you mean the AM21 OTA tuner that plugs into the USB port of a DVR.
Yep, it's for Over-The-Air tuning only. Cable tuners are a whole 'nother animal.
As for picture quality, I've always thought that OTA was superior to cable due to less compression and higher bit rates, but then I haven't had cable since I got DirecTV in '98, which was pre-HD.

-Steve- Subscriber since Sept 1998  My Complete Setup 

SWM16 / HR44-500 (2TB & AM21) / HR34-700 (3TB & AM21) / HR24-500 (2TB eSATA) / C31 via WCCK / C41 x2 / C41W / H25-700


#3 OFFLINE   CCarncross

CCarncross

    Hall Of Fame

  • Registered
  • 7,058 posts
  • LocationJackson
Joined: Jul 19, 2005

Posted 05 October 2012 - 01:50 PM

I tried searching for this and didn't come across anything. I am wondering if the AR21 will only receive OTA channels. Will it receive limited cable channels or not? I figure the answer is no, but I thought I'd ask anyway. Sadly, cable offers better PQ on locals than DirecTV does even when going through the AR21.


As said its an ATSC tuner only, it doesnt handle QAM signals....If you are seeing that cable offers better PQ than OTA then something is wrong with your setup. OTA is the best signal you can get into your home under almost all circumstances. Many local stations I believe broadcast at close to 19MB/s for their OTA feed if they are not using sub-channels. Sat and cable don't even come close to that. What you're describing is virtually technically impossible for cable to offer better PQ than OTA. If you cant receive the stations well via OTA that would be an entirely different discussion.

#4 OFFLINE   harsh

harsh

    Beware the Attack Basset

  • Registered
  • 19,187 posts
  • LocationSalem, OR
Joined: Jun 14, 2003

Posted 05 October 2012 - 01:52 PM

More specifically, the AM21 receives only ATSC channels. QAM (cable) and NTSC (old school broadcast) are not among its capabilities.

Another issue is that you may not have expected is that it will only tune channels that DIRECTV knows about when used with boxes other than the HR34. Only the HR34 can scan for channels not already in the DIRECTV guide.

Too often we enjoy the comfort of opinion without the discomfort of thought. -- JFK


#5 OFFLINE   MRM

MRM

    AllStar

  • Topic Starter
  • Registered
  • 96 posts
Joined: Sep 10, 2008

Posted 05 October 2012 - 01:58 PM

I'm sorry, I meant AM21. Thanks for the replies.

#6 OFFLINE   harsh

harsh

    Beware the Attack Basset

  • Registered
  • 19,187 posts
  • LocationSalem, OR
Joined: Jun 14, 2003

Posted 05 October 2012 - 01:59 PM

If you are seeing that cable offers better PQ than OTA then something is wrong with your setup.

Just as DIRECTV does in several markets, cable sometimes grabs the "pre-modulation" signal that is not hammered like the modulated signal is. My local Comcast does this with at least our ABC affiliate (KATU). We even get a doctored version of the local news.

Perception is also dependent on what kind of proc amp profiling the carrier does. Many think a overly color saturated and extremely contrasty image is better. We usually recognize these types as fans of plasma displays running in torch mode.

Too often we enjoy the comfort of opinion without the discomfort of thought. -- JFK


#7 OFFLINE   weadjust

weadjust

    AllStar

  • Registered
  • 95 posts
  • LocationTupelo, MS
Joined: May 09, 2008

Posted 05 October 2012 - 03:21 PM

My ABC HD OTA is on a sub channel 9-2 and the picture quality is not as good as the Directv ABC HD. OTA pixilates during fast moving sports like football and nascar. Not a problem on the Directv version.

On all the other networks OTA has a better picture than Directv version.

#8 OFFLINE   jimmie57

jimmie57

    Hall Of Fame

  • Registered
  • 3,698 posts
  • LocationTexas City, TX
Joined: Jun 26, 2010

Posted 05 October 2012 - 03:32 PM

I would think the pics from the AM21 are only as good as the antenna feeding it and the local channel's broadcast quality.
I get pixelating on my OTA on 2 channels and I am not using an AM21. I am actually further away than my antenna is supposed to work. If I had a better one I feel certain that problem would go away.

DirecTV customer since 1996 - Current :Slimline 3 SWM,   HR24-100 HDMI to 32" Sharp LED,
HR24-100 Component cables to 46" Samsung LCD & Optical Cable to Yamaha AVR, H21-200 HDMI to Yamaha AVR & HDMI to 52" Mitsubishi LCD


#9 OFFLINE   Racer88

Racer88

    Icon

  • Registered
  • 801 posts
Joined: Sep 12, 2006

Posted 05 October 2012 - 04:24 PM

As said its an ATSC tuner only, it doesnt handle QAM signals....If you are seeing that cable offers better PQ than OTA then something is wrong with your setup. OTA is the best signal you can get into your home under almost all circumstances. Many local stations I believe broadcast at close to 19MB/s for their OTA feed if they are not using sub-channels. Sat and cable don't even come close to that. What you're describing is virtually technically impossible for cable to offer better PQ than OTA. If you cant receive the stations well via OTA that would be an entirely different discussion.


LOL you do realize that more and more locals are cramming 2 HD channels in that 19MBps making them both look like s***? Even some cram more 480 sub channels in than they really should too. Also, as in my case, as well as others by now I'm sure, the long time afflliate to one of the big 4 networks adds a second network on a SD only OTA sub-channel but does provide a HD fiber feed of that same newly added network to the DirecTV, DISH, the local cableco, etc.

So, no OTA is not always "the best you can get" under many circumstances.

(not to mention my local ION affiliate is a low power, SD only station, and there is no CW OTA option at all. Both of which are now in beautiful HD on DirecTV.)

Edited by Racer88, 05 October 2012 - 04:33 PM.


#10 OFFLINE   TomCat

TomCat

    Broadcast Engineer

  • Registered
  • 3,638 posts
Joined: Aug 31, 2002

Posted 05 October 2012 - 05:14 PM

...Many local stations I believe broadcast at close to 19MB/s for their OTA feed if they are not using sub-channels...

CC. I think you are exactly on point on everything else you said, but it is unusual for a TV station to broadcast a single channel at a bit rate higher than about 15 mbps. There are exceptions, of course.

One of the biggest reasons is that the difference between MPEG-2 using modern encoders at 15 mbps and at 18 mbps is imperceptible to some 98% of viewers. Another is that if you send out that stream to cable or sat, they are more likely to truncate it back down to 12 or so anyway, with MPEG-4 vendors truncating it to about 7.5 (done in the MPEG-4 conversion process), which means they are throwing those bits away anyway, for some 90% of viewers (OTA commands about only 10% of all viewers).

What many folks have a difficult time understanding is that if there are enough bits at say 13.5 mbps to encode without motion artifacts, that the same signal encoded at 18 mpbs will be mathematically identical, meaning that the PQ will be absolutely identical, even at a lower rate. If the encoder decides at any one moment in time that it needs fewer bits, the rest of the 19.39 is simply filled with stuffing bits, which do not contribute at all to PQ.

When there is motion enough to starve the bitstream at 13.5 (the encoder begins to call for more bits than are available) then there may be a perceptible difference because there are not enough bits to encode without artifacts (assume a 19.39 channel, but a ceiling placed at 13.5). But that happens usually only on fast motion, and we can't perceive detail in motion in the human vision system in real life anyway, so the perceptual coding used there effectively all but masks any artifacts. IOW, we really don't see any difference.

Encoders from just a few years ago had trouble with scene changes, trouble with fade-ups and fade-downs, and much more trouble with motion. These things stuck out like a sore thumb for most stations, even if they raised the bit rate to 18, but most stations are on 2nd or 3rd-gen encoding by now, and most if not all of those problems have been solved. For instance, most signals insert an I-frame directly at every scene change, regardless of where it would naturally fall in the GOP, and so scene changes are no longer an issue. Newer TVs have decoders that can take advantage of some of the fine-tuning to encoding that has incrementally improved PQ at the same time, and HD and digital production chains have dramatically improved SD and SD upconverted to HD.

And certainly, stations with more subchannels have more of these issues than those that do not. But what is interesting is the political issues involved. If station A encodes at 12.5 and puts out a reasonably good-looking picture, the argument from the government is that all stations should do that, "and by the way we (the government) want that bandwidth that you are not using anymore back so we can sell it to AT&T." So the government is effectively squeezing the PQ of OTA stations, and the technology (given PQ at a given bit rate) gradually improves at the same time, offsetting that.

Stations have responded by adding mobile TV and subchannels to fill the 19.39 so that the government can't as easily make that argument, and many times the added signals are not profit centers at all, just placeholders. So look to see that in the near future most ".1" HD signals will be broadcast at closer to 12 mbps than 15 or 18. And of course anyone who has watched a CBS station during March Madness, or who is blessed with a station that has subchannels and doesn't encode as artfully as maybe they should, knows that PQ can and does suffer when we get to lower rates such as this.
It's usually safe to talk honestly and openly with people because they typically are not really listening anyway.

#11 OFFLINE   carl6

carl6

    Hall Of Fame

  • Moderators
  • 11,148 posts
  • LocationSeattle, WA
Joined: Nov 15, 2005

Posted 05 October 2012 - 05:15 PM

Too many variables involved to say whether the OTA signal is better or worse than satellite or cable. However, it is strange that your primary ABC channel is on 9-2 rather than 9-1. Almost always, the primary (and HD) channel is the -1, and a secondary (SD) channel is -2. But that is something the local station can change if they want to.

Some of the variables involved include how DirecTV, Dish, or the cable company happen to get the signal from the station. Some capture it off-air, some may get a direct feed from the station, and that feed can vary in terms of quality. It can be different from station to station, market to market, and provider to provider. In other words, cable might get a fiber feed from the station while the satellite companies are picking up the OTA signal and using that. Or the reverse.

#12 OFFLINE   TomCat

TomCat

    Broadcast Engineer

  • Registered
  • 3,638 posts
Joined: Aug 31, 2002

Posted 05 October 2012 - 06:01 PM

LOL you do realize that more and more locals are cramming 2 HD channels in that 19MBps making them both look like s***? Even some cram more 480 sub channels in than they really should too. Also, as in my case, as well as others by now I'm sure, the long time afflliate to one of the big 4 networks adds a second network on a SD only OTA sub-channel but does provide a HD fiber feed of that same newly added network to the DirecTV, DISH, the local cableco, etc.

So, no OTA is not always "the best you can get" under many circumstances...

Well, for that particular signal, yes it absolutely is. That signal is the original consumer source; it's "patient zero", and that is the signal distributed to cable, sat, fiber, and what-have-you (stations and/or networks do not encode at 18.5 and send that to cable over a fiber link then also encode at 12.5 and send that OTA), meaning that whatever secondary vendors do to it from that point on only has the potential to reduce the PQ, and nothing they can do can improve the PQ (which is so far technically impossible). No better source signal is available to any consumer via any path. That makes the OTA signal the best signal available among signals derived from that original source (and virtually all come from that original OTA source). It is possible for cable to match it, assuming they are careful (DBS converts to MPEG-4 so they can't match it) but it can not technically be better than OTA, and cable often squeezes the signal further anyway.

I sincerely doubt that you can come up with a scenario where there is a better-quality signal available that is a mirror of an off-air signal, because of the reason above and also because there is no practical way to deliver those signals outside of the station path in any way that can support higher bit rates than the station is using, other than after-the-fact blu-ray (and good luck getting a copy of this week's Fringe episode there, or ever for a decent price).

CC qualified his post with "if they are not using subchannels", so it is readily apparent that he is aware of the side-issues you have brought up; he just chose not to go there.
It's usually safe to talk honestly and openly with people because they typically are not really listening anyway.

#13 OFFLINE   TomCat

TomCat

    Broadcast Engineer

  • Registered
  • 3,638 posts
Joined: Aug 31, 2002

Posted 05 October 2012 - 06:34 PM

My ABC HD OTA is on a sub channel 9-2 and the picture quality is not as good as the Directv ABC HD. OTA pixilates during fast moving sports like football and nascar. Not a problem on the Directv version.

On all the other networks OTA has a better picture than Directv version.

You are very likely receiving WTVA, which is a primary NBC station, and carries the HD version of NBC on 9.1. An OTA station can't carry more than one HD stream; there just are not enough bits in 19.39 to do that. There is no primary ABC station in that area, so my best guess is that WTVA carries ABC on a subchannel, 9.2, in SD (they can still carry it as 16:9).

The DTV ABC channel is an imported OTA HD channel, so it will very likely have better PQ than 9.2 will, because even though OTA, 9.2 is only SD.

So there is the odd scenario that somewhat, sort of breaks the rule, although we must remember that the original source of the DTV ABC channel is a distant-import full HD OTA station, meaning that an original OTA station is still the signal with the best PQ, even in this rare scenario.
It's usually safe to talk honestly and openly with people because they typically are not really listening anyway.

#14 OFFLINE   Oogie Pringle

Oogie Pringle

    Cool Member

  • Registered
  • 18 posts
Joined: May 24, 2008

Posted 06 October 2012 - 07:34 AM

Another issue is that you may not have expected is that it will only tune channels that DIRECTV knows about when used with boxes other than the HR34. Only the HR34 can scan for channels not already in the DIRECTV guide.


I was thinking about getting one of these, but this gave me pause. I live midway between Washington and Baltimore. Because of my zip code, I can only get the Baltimore locals through DIRECTV. Does the above mean that I won't be able to get the Washington locals with an AM21?

And I don't have an HR34.
Thanks

Edited by Oogie Pringle, 06 October 2012 - 07:35 AM.
Added bit about HR34


#15 OFFLINE   carl6

carl6

    Hall Of Fame

  • Moderators
  • 11,148 posts
  • LocationSeattle, WA
Joined: Nov 15, 2005

Posted 06 October 2012 - 07:42 AM

I was thinking about getting one of these, but this gave me pause. I live midway between Washington and Baltimore. Because of my zip code, I can only get the Baltimore locals through DIRECTV. Does the above mean that I won't be able to get the Washington locals with an AM21?

And I don't have an HR34.
Thanks


The AM21 allows you to scan for TWO markets/zip codes (with any receiver or DVR). But it only shows you the channels that DirecTV has in it's guide data for those two markets. The HR34 will scan and find channels that are not in the DirecTV guide data.

You should be fine for what you want to do, so long as you have acceptable off-air signal levels.

#16 OFFLINE   Gary Toma

Gary Toma

    UNIX

  • DBSTalk Club
  • 1,907 posts
Joined: Mar 22, 2006

Posted 02 November 2012 - 04:18 PM

For those of you knowledgeable on the AM21 please -

A question from a user in Argentina: They are able to tune OTA channels using the AM21. The problem is that when he turns to channel 22, it gets 'stuck' or hung up there.

Channel 22 appears like this in our Latin TPN Map tab:

527|ENCUE|22.1||OTA|_|22||Argentina|Encuentro
527|PAKAP|22.2||OTA|_|22||Argentina|PAKA-PAKA
527|TVPub|22.3||OTA|_|22||Argentina|TV Publica
527|INCA|22.4||OTA|_|22||Argentina|INCAA TV



Any past experiences with problems like this?


#17 OFFLINE   carl6

carl6

    Hall Of Fame

  • Moderators
  • 11,148 posts
  • LocationSeattle, WA
Joined: Nov 15, 2005

Posted 02 November 2012 - 10:02 PM

I have no idea if the AM21 will work in the Latin America market. This would be dependent on the software/firmware in the DVR or receiver it is connected to as it would the AM21 itself. I wasn't aware they worked at all outside the US.

#18 OFFLINE   ThomasM

ThomasM

    RF Engineer

  • Registered
  • 4,317 posts
  • LocationMilwaukee, WI
Joined: Jul 20, 2007

Posted 03 November 2012 - 07:19 PM

As said its an ATSC tuner only, it doesnt handle QAM signals....If you are seeing that cable offers better PQ than OTA then something is wrong with your setup. OTA is the best signal you can get into your home under almost all circumstances. Many local stations I believe broadcast at close to 19MB/s for their OTA feed if they are not using sub-channels. Sat and cable don't even come close to that. What you're describing is virtually technically impossible for cable to offer better PQ than OTA. If you cant receive the stations well via OTA that would be an entirely different discussion.


That's not true. If the cable system has a fiber-optic feed from the broadcast OTA station and that same OTA station has a bunch of subchannels, it is entirely possible that the QAM HD cable feed is superior.

3LNB Phase III Dish * 2-R15-300 * R22-200 * D12-100 * DirecTV Subscriber since Y2K


#19 OFFLINE   CCarncross

CCarncross

    Hall Of Fame

  • Registered
  • 7,058 posts
  • LocationJackson
Joined: Jul 19, 2005

Posted 03 November 2012 - 10:07 PM

Already pointed out over a month ago..thanks for bringing it up again. Luckily, my market doesnt do that, but apparently many others now do.

#20 OFFLINE   TomCat

TomCat

    Broadcast Engineer

  • Registered
  • 3,638 posts
Joined: Aug 31, 2002

Posted 04 November 2012 - 12:24 AM

... If the cable system has a fiber-optic feed from the broadcast OTA station and that same OTA station has a bunch of subchannels, it is entirely possible that the QAM HD cable feed is superior.

Technically it is "possible", but quite often (if not always) not "entirely possible", because that is somewhat academic. In the real world, that's not really how things work.

The fiber feed sent to cable is typically already shaped and encoded at whatever rate the TV station is also using for that same signal that they broadcast. In fact, it is the same signal. TV stations do not encode differently for their transmitter exciter than they do for direct closed fiber feeds to cable and sometimes DBS, because there is no motivation to do that. In fact, quite the opposite; it would cost much more, decrease QoS reliability, and add to complexity and maintenance overhead. Some stations receive their network signals already crunched down, precludiong them completely from even entertaining the thought.

TV typically encodes just once, to fit SMPTE310, and that same signal gets sent usually via an ASI stream, sometimes via TCP/IP, via fiber to secondary cable vendors. Everybody gets the same signal, and the same PQ. Cable demuxes the channels of interest and eventually QAM modulates them, both processes being completely transparent to the data that comprises the picture and sound information.

Sometimes they further compress, but rarely, and this means that cable can and usually does duplicate the PQ of the OTA signal, because the binary coefficients that represent the pixel information are never modified and they stay unchanged within the digital domain until they get to the decoder in your STB. If the math is not changed, the PQ can't change. Unless a zero can magically turn into a one, or vice versa, everything stays locked exactly the same, and since math is an abstract construct, there is nothing within the hostile transport environment that can achieve that.

In analog, the message is intimately tied to the medium, and if something degrades the medium, it degrades the message along with it. In digital the message is not tied to the medium (that abstract construct thingy once again) meaning that the medium can be degraded, up to a point, without that touching or altering the integrity of the message, even a little bit.

There is jitter, but that gets reclocked in the decoder. There is carrier degradation, but not information degradation. A written note with a phone number on it can go through the wash and bleed and smear, but if you can still extract the information by reading it, it is identical to the same information used to write the number down in the first place, for example. You still have all of the information even though the medium carrying it to you might be degraded, and that is the analogy here.

The message is not the squiggles on the paper, instead it's a number, which is also an abstract construct rather than something that exists in the physical realm. If one or more of the digits in that note are degraded too much to make out, the entire information is invalid and you can't call the number, which is the same analogy as the digital cliff, where you either have all of the information intact, or none of it, like when the signal degrades enough for your screen to mute to black. If you can make out part of the smeared digit and make a correct educated guess, you then have the entire information once again, which is the analogy for error correction.

DBS is a little different because of the added MPEG-2 to MPEG-4 step, which adds inevitable rounding errors to the information, which alters the binary math slightly, which potentially can manifest as PQ degradation. But both DBS vendors seem to do it cleverly enough so that we generally don't see the difference, regardless of how closely we look or how golden our eyes might be.

Bottom line, it makes more sense to record the signal via sat and save HDD space than it does to record it OTA. The trade-off is the potential degradation in the conversion process, but if done right and you can't see the difference, the smart move would be to forgo OTA for DBS, assuming you have both available, unless recording space is so abundant so as not to need management, which it never is.

Edited by TomCat, 04 November 2012 - 12:50 AM.

It's usually safe to talk honestly and openly with people because they typically are not really listening anyway.




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