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Tuning HD Channels

post #1 of 11
10/25/08 at 9:25pm
Thread Starter 
Gang -

My Samsung LN40A550 has a QAM tuner and I'm able to tune the network channels in HD by entering 4-1 or 5-1 or 7-1. I believe that Comcast does not scramble their HD channels such as ESPN-HD. Should I be able to tune them directly? When I enter 849 (the channel # that Comcast uses for ESPN-HD) I don't get anything. There are no 'traps' or filters on the pole since my TiVo (with cable cards) can tune these channels.

Thanks in advance.

Bob
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post #2 of 11
10/25/08 at 10:59pm

Re: Tuning HD Channels

Quote:
Originally Posted by rcoates777
Gang -

My Samsung LN40A550 has a QAM tuner and I'm able to tune the network channels in HD by entering 4-1 or 5-1 or 7-1. I believe that Comcast does not scramble their HD channels such as ESPN-HD. Should I be able to tune them directly? When I enter 849 (the channel # that Comcast uses for ESPN-HD) I don't get anything. There are no 'traps' or filters on the pole since my TiVo (with cable cards) can tune these channels.

Generally only your local broadcast channels will be unencrypted along with a handful of other stations. ESPN is usually encrypted and you need a cable box or cablecard device to tune it.
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post #3 of 11
10/26/08 at 4:35am

Re: Tuning HD Channels

We have Comcast, and they do indeed scramble the non-local HD channels such as ESPN, ESPN2, etc. You need a HD cable box in order to receive those channels.

We have a Vizio 37-inch LCD in our bedroom with a QAM tuner and no cable box. We can get the local CBS, ABC, NBC, Fox and PBS affiliates in HD, plus the extra sub channels used by the local stations for weather and a "Nick at Nite" type channel called RTN that is owned by the local ABC affiliate.
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post #4 of 11
10/26/08 at 5:53am
Thread Starter 

Re: Tuning HD Channels

Stephen, Scott -

Thanks for your responses. The whole channel numbering business is a little confusing to me. My local HD channel 4 is tuned by entering 4-1 on the Samsung. But on the TiVo it's 804. I imagine that somehow both these designations end up at the same frequency. I have read that one of the primary functions of the cable card is a mapping function - not just de-encryption.

But it sounds like the concensus is that all my HD channels (other than the network versions) are encrypted. Thanks again.

Bob
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post #5 of 11
10/26/08 at 7:40am

Re: Tuning HD Channels

Quote:
Originally Posted by rcoates777
Thanks for your responses. The whole channel numbering business is a little confusing to me. My local HD channel 4 is tuned by entering 4-1 on the Samsung. But on the TiVo it's 804. I imagine that somehow both these designations end up at the same frequency. I have read that one of the primary functions of the cable card is a mapping function - not just de-encryption.

I get some strange mappings in our household, too, Bob. The local CBS affiliate is channel 62 over the air. On the QAM tuner on our bedroom Vizio 37" LCD, the HD channel is 84-1, while on the QAM tuner of the Samsung 67" DLP in the main HT room it's 62-1. All other local HD channels map identically to their over the air channel numbers on both sets' QAM tuners, though.
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post #6 of 11
10/26/08 at 8:01pm

Re: Tuning HD Channels

Quote:
Originally Posted by Scott Merryfield
I get some strange mappings in our household, too, Bob. The local CBS affiliate is channel 62 over the air. On the QAM tuner on our bedroom Vizio 37" LCD, the HD channel is 84-1, while on the QAM tuner of the Samsung 67" DLP in the main HT room it's 62-1. All other local HD channels map identically to their over the air channel numbers on both sets' QAM tuners, though.

It's not that strange if you understand what's going on. On cable there are 3 numbers to deal with:
1. The actual physical cable channel #. 84 in the above case. (The -1 is the subchannel). These channel numbers are different from over-the-air channel numbers which use different frequencies in the UHF band than cable does. This is totally arbitrary, the cable company fits in the channel wherever they have room on their system. No need to match the OTA channel #, and usually they can't since there is something on that channel already (e.g. the analog channel).

2. The PSIP channel number. 62-1 here, often set to match the over-the-air channel #. This is based on data embedded in the digital signal. But sometimes it can be screwed up in such ways that some TV tuners can handle but others can't, hence the difference between the Samsung which managed to handle it while the Vizio does not. If the PSIP fails intermittently on the other sets, you may have to tune to the actual physical ch #. Or if the cable company decides to move the physical channels around you may have to do a rescan as the stored mapping in the TV may no longer match reality.

3. Cable company channel #, as used on their cable boxes and cablecard devices. This again is completely arbitrary, they use 3/4 digit numbers and don't use subchannel #s.
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post #7 of 11
10/27/08 at 4:49am

Re: Tuning HD Channels

Thanks, Stephen. I understood that our cable company may be using a different channel number than the over the air broadcast, but didn't realize that different TV QAM tuners could fail to detect a remapping while others could. That explains the 62-1 vs. 84-1 channel issue I'm having for our CBS affiliate. It's not a big deal, as long as we can find the stations.

Actually, it's even less of an issue, since I almost always use the HD cable box with the Samsung in our main HT room, and I can never remember the channel numbers for any of those channels. I either use the on screen guide, or the favorite channels feature of my Harmony remote for that TV.
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post #8 of 11
10/27/08 at 7:27am
Thread Starter 

Re: Tuning HD Channels

Stephen -

Good information, thanks. What does PSIP stand for? Does it get transmitted in each physical channel #? (That is, channel & subchannel) Is its function to map a cable company channel #? (e.g. 843) to a physical channel # (e.g. 62-1).

And since cablecards and STBs use the 3 or 4 digit cable company channel #'s this PSIP data provides a mapping to get to the actual physical channel, right?

But I must be missing something because in Scott's case he had 2 TV's that found the same show on 2 different physical channels. Do the channel/sub-channels have fixed frequencies? If so it would seem that his CBS show should always be on a particular channel/subchannel and not vary from set to set. And I wouldn't think that the PSIP data would even matter.

Where did I go wrong?

Thanks.
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post #9 of 11
10/27/08 at 8:02am

Re: Tuning HD Channels

Bob,

Here is a link that spells out PSIP pretty well. PSIP is metadata regarding the broadcast, such as station call sign, time of day, channel mapping, etc. So, depending on how the TV tuners decodes the PSIP information will account for differences like what I am experiencing on the QAM tuners of two different TV's attached to the same cable TV system.
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post #10 of 11
10/27/08 at 10:00pm

Re: Tuning HD Channels

Quote:
Originally Posted by rcoates777
And since cablecards and STBs use the 3 or 4 digit cable company channel #'s this PSIP data provides a mapping to get to the actual physical channel, right?

The PSIP maps from physical channel # to the displayed channel # when using the TV's built-in tuner (along with the other stuff mentioned in the wikipedia article). Cable boxes/cablecards use a different scheme for the 3 digit cable company #s, some other protocol.

Quote:
But I must be missing something because in Scott's case he had 2 TV's that found the same show on 2 different physical channels. Do the channel/sub-channels have fixed frequencies? If so it would seem that his CBS show should always be on a particular channel/subchannel and not vary from set to set. And I wouldn't think that the PSIP data would even matter.
No it was only one physical channel. One set couldn't decipher the PSIP and thus just displayed the physical channel # instead of the PSIP defined #.

Physical channels have fixed frequencies, but the cable company can change what channel is located where at any time; they move stuff around sometimes when adding new channels forcing a rescan. The PSIP display # is arbitrary although usually set to match the OTA channel #. Subchannels are just different programs being broadcast on the same frequency but using different program IDs, the tuner just grabs the video/audio that belong to the program you selected and discards the data for the other subchannels.
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post #11 of 11
10/28/08 at 5:33am
Thread Starter 

Re: Tuning HD Channels

Great response. It's starting to make sense! Thanks again. BobC
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