QAM vs. OTA (What can antenna get that cable cannot?)

Your antennae will pick up any Local OA stations that are not carried by your cable co.

There may also be some HD locals that your cable company doesn't carry - they might only have them digitally in 480i. For example, CW, MyNetwork or smaller, locally originating channels.

There may also be some OTA subchannels that the cableco may not carry.

OTA is your only guarantee of uncompressed HD. Most Cable providers compress the signal resulting in a loss of resolution or some digital artifacts. That's right you can get a nice 1920x1080i signal from a $12 set of Rabbit Ears while you might get a not as nice 1280x1080i signal complete with digital artifacts from your cable/sat provider and pay north of $70/month for the privilege.

Time Warner and Cox, two of the larger cable companies, state that they pass through whatever they receive i.e. if they receive 1920x1080i that is what they send over their lines. If you are dealing with any of the other companies, and are concerned, you may wish to check with them to see what they send. Satellite is known for "HD-Lite"

OTA is no guarantee of uncompressed HD. Sub-channels and USDTV have a way of eating up bandwidth.

That's true. The signals are compressed however compression does not necessarily mean a reduction in resolution. I asked a question about "HD-Lite" on a broadcast engineer thread and the reply was that the stations broadcast at 1920x1080 at 1080i and ".....besides it would cost $$$$ to side convert from 1920 to 1280...and nothing is gain by it."

Time Warner may claim that they send the local channels without change, but they need to change it from RF format to QAM format.

I purchased an OTA antenna because my local channels on Time Warner were frequently showing artifacts or losing sound.

The OTA signal seems to be much more stable and shows a higher quality picture.

Come on. You know that is not what was meant. They do NOT change the resolution. There was no claim that overcompression does not impact the display only that when 1080 is the claimed resolution 1920x1080 is being sent.

I have 2 TV's both with QAM tuners. I was able to receive over the air high def channels on the upper channels before the channel line up change today. Any idea why I am not getting those channels any longer since they are over the air. Has anyone noticed this also. Is there anyway to get them back. I called Time Warner and the operators there have no clue.

In the long term cable cos may have more than just the locals in clear QAM. While it changes often you sometimes can get cable only chs in clear QAM. You also sometimes can get your neighbor's VOD via the QAM tuner.

A 2 RF input TV is the best way to go.

Cable cos change the ch lineups fairly frequently. Do another scan and you should be able to find them again - probably just moved to a different ch.

I tried a full scan this morning when I noticed they were gone and now I just get a lot of blank channels. Could it be Time Warner started scrambling them?

They might have. I think (am not sure) that some cable companies do scramble them.

Best to ask this in your local area thread - folks in the area would have the scoop on what the local cable co is doing with their clear QAM chs.

A lot of misinformation in this topic.

- Comcast is the main cableco that in most cases does not alter HD image quality. The exception is some of their older cable system acquired from other companies.

- TWC, Charter & Cox are noted for using rate shaping to pack more HD in the same space, as were AT&T and Adelphia.

- Don't expect pristine HD from local OTA, unless they don't multicast, which many local HD stations do.

- Re-modulating from ATSC (OTA) to QAM (cable) does not, in and of itself, reduce HD quality.

Also, in some areas (especially rural ones) you can pick up OTA stations that your cable company is not allowed to carry because they are "out of market" and would compete with stations in your own Designated Marketing Area (DMA). For example, I live on the fringe of the Greenville SC DMA so if I had cable, it would carry only Greenville-area "local" stations. However, with my roof antenna I can also receive stations from Columbia SC and Charlotte NC (and on a good night, Augusta GA).

That's true. I'm in the Chicagoland area, and I get many channels from Rockford and Milwaukee also. Even South Bend, Ind. and Quad Cities, IL/IA occasionally, on good tropo nights.

And, in answer to jling84's question about QAM - you'll get anything the cable company leaves in the clear. Usually, their website will tell you which digital channels are available with limited basic, which is what you should get on QAM.

QAM tuner will be able to pick up channels that are provided by your cable co that are unscrambled. For Instance for me that means that I can get the Local HD channels that my Cable Company Provides (not all of them since they do not have an agreement to carry some of the local channels)., I was able to get ESPN for free as well, but from reports it looks like that has ended.

If you go channel by channel sometimes you can find "leak" feeds through your QAM as well. For me on certain channels Ill get leak feeds of what people are ordering through OnDemand sometimes its good sometimes its bad you jsut have no control of it and it goes in and out but hey its free.

Hope this hlps

Cox HR states that they compress but do not otherwise alter signals. They send out what they receive. "if you view the MPEG-2 stream by firewire you'll see that it does appear to be in the native format. Most channels are 1920x1080i, ESPN HD is 1280x720p."

The HR local OTA stations multicast and also compress the signals but do not reduce the resolution. These are from a couple of the local station broadcast engineers: I don't know where this HD Lite 1240x1080 stuff is coming from, since that would result in a nearly square picture (maybe 4x3 if the pixels were rectangular). I can tell you that we gave full 1920 x 1080i when I was at WGNT and WTKR...The 18 formats are stored as tables in the chipset...any thing not matching it, causes A) black picture or B) horrible pixilation.....besides it would cost $$$$ to side convert from 1920 to 1280...and nothing is gain by it.

I can confirm that Cox in Phoenix, AZ does no recompression or rate shaping of local channels. Every time one the locals decide they want to add another f@#$ing subchannel to their DTV broadcast, the Cox bitrate follows the OTA bitrate right into the crapper. I can't speak for the other HD channels, however.

When my cable company changed from Cox to Suddenlink, they took away my free Starz channel through QAM....LOL....bastards.

I know what Cox says.


The resolution is not the sole determining factor. If they are multicasting, they are taking away bits from the HD channel, even if the resolution is ATSC standard. Multicasting directly affects HD image quality.

That does not confirm anything regarding what they do to the HD locals they retransmit.

All it does is confirm that as more subchannels are added, HD image quality will get worse. When Cox is reducing bits, it's downstream of what the local HD stations are doing. To prove this, look at the same channels directly from OTA & Cox.

Done and done. The streams are identical. Cox has no reason to perform any sort of picture mutilation because they aren't adding anything to their 38.4 mbit/s QAM channels besides the contents of 2 19.2mbit/s 8VSB channels. All of the QAM channels carrying locals have some amount of nullpackets, ranging from around 1mbit on the channel with PBS HD, PBS SD, NBC HD, and NBC W+, to around 10mbit/s on the channel with 13.5mbit/s ABC HD and 14.5mbit/s CBS HD (neither station's .2 subchannel is carried). As for the other channels such as iNHD, I can't compare since I don't have access to the C-Band feeds or the cable streams anymore since Cox is now 5Cing everything but the locals.

i have the lg 32lc3du model. After reading this forum (which rocks) I believe this tv has a qam tuner. How do i use it and what do i hook up to check to see if I have any free hd channels?

Also, How do you access the service menu on the tv? I read you hold down the menu button for specific period of time and I did that and a 4 digit password comes up... what is the code for a lg out of the box?

Thanks,

Scott

Connect your cable feed to the RF input of the TV and do a ch scan.

Ask about the service menu in the flat panel threads.

Be careful here, I have 2 RF inputs on my TV, BUT, you can only hook up an OTA antenna to RF1 and if you want to use QAM, you can only hook up to - you guessed it - RF1. RF2 is an NTSC tuner only, which is useless today on an HDTV, nevermind in 2009. RF1 is an OTA/QAM hybrid tuner. I suspect many TVs are like this regardless of having 1 or 2 RF inputs.

I guessed I assumed too much - my Sony ( and I thought most other makers) have the QAM tuner on the input labeled Cable and the NTSC/ASTC tuner on the OTA labeled input. Actually on my Sony you can get NTSC on the cable input as well.