Understanding QAM Mapping on Premeire

[jaywtivo]

I consider myself an amateur TV geek. I would say I know more than joe public, but I'm not an engineer.

Just as soon as I think I figured out QAM/ATSC crap, I buy a TiVo.

So why does my cheap WalMart TV with no CableCard and a QAM tuner, map the cable channels I receive differently than my Tivo. (THE TV is not decrypting any channels, just displaying Clear QAM straight from the wire.)

For instance:
Local Digital Channel 2 on my TV is at 202
On my TiVo, its 233, but wait on my HDHomeRun it's got a Tuner Channel, and a guide channel and neither are the same...

Tuner: 81-2 Guide: 234

Can someone please explain to me how this works?

[LoREvanescence]

I consider myself an amateur TV geek. I would say I know more than joe public, but I'm not an engineer.

Just as soon as I think I figured out QAM/ATSC crap, I buy a TiVo.

So why does my cheap WalMart TV with no CableCard and a QAM tuner, map the cable channels I receive differently than my Tivo. (THE TV is not decrypting any channels, just displaying Clear QAM straight from the wire.)

For instance:
Local Digital Channel 2 on my TV is at 202
On my TiVo, its 233, but wait on my HDHomeRun it's got a Tuner Channel, and a guide channel and neither are the same...

Tuner: 81-2 Guide: 234

Can someone please explain to me how this works?

The tuner channel, 81-2 is where the channel is actually located on the cable system.

The guide channel is the virtual channel number assigned by the cable company. However, unless you have a cable card, your tivo can't pick up the virtual channel mapping from the cable system, there for the channel appears in a different spot then the guide data. Your tivo is designed to work with the cablecard, with out it, there is no support for guide data.

As for your tv, I have no idea where it's picking up 202.

[aaronwt]

The tuner channel, 81-2 is where the channel is actually located on the cable system.

The guide channel is the virtual channel number assigned by the cable company. However, unless you have a cable card, your tivo can't pick up the virtual channel mapping from the cable system, there for the channel appears in a different spot then the guide data. Your tivo is designed to work with the cablecard, with out it, there is no support for guide data.

As for your tv, I have no idea where it's picking up 202.

If the cable system is set up right, it would show up as 2-1, 2-2, etc. on the Tv QAm tuner just as if you were getting it from OTA. This is how Comcast and FiOS is setup in my are. You plug the cable into your TV with aQAM tuner and all the local channels show up as if you were using an OTA antenna.

[LoREvanescence]

If the cable system is set up right, it would show up as 2-1, 2-2, etc. on the Tv QAm tuner just as if you were getting it from OTA. This is how Comcast and FiOS is setup in my are. You plug the cable into your TV with aQAM tuner and all the local channels show up as if you were using an OTA antenna.


I don't think it has so much to do with how the cable system is set up. It all depends on if the local channels own OTA mapping data is set up correct, or exists. Don't most cable systems just pass the locals signals leaving it virtually untouched. My guess is this channel is missing OTA Mapping.

But yes, if the channel had it's own Mapping, it would show up in the OTA Mapped location of 2-1 on the TiVo. The cable companies Mapping overrides that to 233.

In any event, to get the correct mapping for the guide data you will still need a Cable Card, if it was mapped to 2-1 you would still not have the guide data and the guide data would be on channel 233

[lessd]

The tuner channel, 81-2 is where the channel is actually located on the cable system.

The guide channel is the virtual channel number assigned by the cable company. However, unless you have a cable card, your tivo can't pick up the virtual channel mapping from the cable system, there for the channel appears in a different spot then the guide data. Your tivo is designed to work with the cablecard, with out it, there is no support for guide data.

As for your tv, I have no idea where it's picking up 202.

A recent channel scan of a TiVo-HD without cable cards added new network ch in the 200 range, so now, as example, I can get HD-CBS on 3-1 (the old OTA was Channel 3) and also the same HD-CBS on channel on 203-1. The assignments keep changing if you don't have cable cards. I have Comcast.

[jaywtivo]

Upon further investigation, my bad:

Clear QAM on the TV:

202-1 is the analog channel. However, the analog channel also shows up at locations 2-0.

2-1 is the digital channel

So the Tivo does not map the channels?

[LoREvanescence]

Upon further investigation, my bad:

Clear QAM on the TV:

202-1 is the analog channel. However, the analog channel also shows up at locations 2-0.

2-1 is the digital channel

So the Tivo does not map the channels?

No, TiVo's do not map the channels, they receive the mapping from the station or cable system. With out any mapping it will just show the actual channel location.

To receive the mapping from the cable system, cable cards are required.

Only OTA stations have their own mapping, and that mapping will show up in clear qam as well only for stations that also broadcast in OTA. However, the OTA Mapping will always be different then the cable systems mapping.

[jaywtivo]

No, TiVo's do not map the channels, they receive the mapping from the station or cable system. With out any mapping it will just show the actual channel location.

To receive the mapping from the cable system, cable cards are required.

Only OTA stations have their own mapping, and that mapping will show up in clear qam as well only for stations that also broadcast in OTA. However, the OTA Mapping will always be different then the cable systems mapping.

I have a cable card and my channels are not mapped on my Tivo. Just on my TV.

[LoREvanescence]

I have a cable card and my channels are not mapped on my Tivo. Just on my TV.

Is the cable card in your tivo, and not your tv?

If the cable card is in the tivo, it may not be configured correctly or activated.

[jaywtivo]

Is the cable card in your tivo, and not your tv?

If the cable card is in the tivo, it may not be configured correctly or activated.

It's activated, as I am getting the decrypted channels.

[jaywtivo]

It's activated, as I am getting the decrypted channels.

On the CableCard Pairing screen, it does say, "In order to start cable service for this device, please contact your cable provider."

Does anyone else with an activated card have this message?

[vstone]

Your TV tuner uses the cable QAM mapping tables built into the ATSC spec. Your Tivo knows to use the mapping tables that the cable company uses, which are different. Assuming that your cable company doesn't receive its local signal OTA, it could choose to map the ATSC tables the same way. It chooses not to. The FCC and Congress don't care if your TV tuner is useful. Your cable company prefers that it not be useful. Their is some language in CFR about supporting customer equipment, but I don't know if it could be applied to this situation.

Your Tivo sans cablecard will use the QAM mapping tables. Since this channel lineup is likley not published, your Tivo would have no way to correlate QAM mapping to program guides, significantly reducing its usefulness.

[LoREvanescence]

On the CableCard Pairing screen, it does say, "In order to start cable service for this device, please contact your cable provider."

Does anyone else with an activated card have this message?


I believe that means you have a pairing issue with your cable card. You will need to call your cable provider and have them try to reactivate / pair the card or try a diffrent one.