How do TV sub channels work?

Verify Boxnut 's comments. I think there is a lot of mis-information contained in the https://www.electro-tech-online.com/threads/how-do-tv-sub-channels-work.159659/post-1384478 post.

We still have physical channels and we have virtual channels under ATSC. The number of channels has been reduced from the early NTSC VHF and UHF assignments primarily for cellular. In many markets VHF has been dropped from ATSC markets.

The information is digital and thus it's all or nothing. You can't ask for a re-transmit of a bad packet.

They claim that ATSC-3 will essentially have IP addresses. https://www.thebroadcastbridge.com/content/entry/6229/atsc-3.0-details-explained-part-4

In ATSC-2 what's very important is the TSID or Transport Stream ID. For every "antenna" or region, like MAC addresses, they are unique numbers. It's important to have that so your tuner has a unique ID for each transport stream. I think you could have a digital channel 2-1 from Philadelphia and digital channel 2-1 from Baltimore and the tuner could figure that out.

KeepItSimpleStupid said:

We still have physical channels and we have virtual channels under ATSC.

Click to expand...

that's true.... i think what's confusing to the OP is the terminology of "subchannel" which would normally mean a real portion of spectrum space, such as in FDM radioteletype, where each separate RTTY link operates on a different pair of frequencies within the FDM channel. but in the case of ATSC, they are "virtual" subchannels, and you can't determine if there are subchannels or not just by looking at a spectrum analyzer or waterfall display of the signal. ou have to decode the bitstream and look at the frame headers and packet headers just like in an ethernet connection. ATSC is very much like ethernet in that like ethernet it uses the standard OSI 7 layer model (minus a few features since it's a one-way transmission method) the OP is expecting subchannels in the frequency domain of the PHY (physical interface Layer 1), but the truth is the subchannel is determined at the Transport (layer 4) or Session layer (layer 5), which are in the software part of the model.

Still some naming conventions used here not exactly correct. There is no longer 'VSB' anything, it is technically a form of OPSK. 8PSK the engineers call it.
cable systems had this a short while then upgraded to QAM 2304 and soon QAM4086 if you can imagine 4000 points on a constellation.
The newer 8PSK PHY has a 30 Mhz channel bandwidth overlapped. Inherent is collision avoidance so they get away with overlapping digital channels
(Yes, a bit like DSL modems)
The full spectrum uses 752 Mhz with gaps for FM broadcast and commercial communications plus guard bands.
The link layer squeezes this into the 67 main channels. As I said, this gets incredibly complicated the deeper you get into this;

yea, it's essentially a 6baseT or 6ANT (made up 6 ANTenna) connection. It has room for 6Mbps worth of data or whatever the fixed number is per physical channel. it's also more like UDP packets where speed is more important than correctness and not TCP/IP where correction is taking place.

it might be wothwhile to look at: https://en.wikipedia.org/wiki/Serial_digital_interface

The MPEG-TS is the digital stream that gets encoded into 8VSB. TS meaning transport stream. That's whats'recoved by the TV.

KeepItSimpleStupid said:

Verify Boxnut 's comments. I think there is a lot of mis-information contained in the https://www.electro-tech-online.com/threads/how-do-tv-sub-channels-work.159659/post-1384478 post.

We still have physical channels and we have virtual channels under ATSC. The number of channels has been reduced from the early NTSC VHF and UHF assignments primarily for cellular. In many markets VHF has been dropped from ATSC markets.

The information is digital and thus it's all or nothing. You can't ask for a re-transmit of a bad packet.

They claim that ATSC-3 will essentially have IP addresses. https://www.thebroadcastbridge.com/content/entry/6229/atsc-3.0-details-explained-part-4

In ATSC-2 what's very important is the TSID or Transport Stream ID. For every "antenna" or region, like MAC addresses, they are unique numbers. It's important to have that so your tuner has a unique ID for each transport stream. I think you could have a digital channel 2-1 from Philadelphia and digital channel 2-1 from Baltimore and the tuner could figure that out.

Click to expand...

True, and there is overhead such as forward error correction and CRC parsing.

8VSB: https://videocide.com/glossary/8vsb/

KeepItSimpleStupid said:

In ATSC-2 what's very important is the TSID or Transport Stream ID. For every "antenna" or region, like MAC addresses, they are unique numbers. It's important to have that so your tuner has a unique ID for each transport stream. I think you could have a digital channel 2-1 from Philadelphia and digital channel 2-1 from Baltimore and the tuner could figure that out.

Click to expand...

No, because you are talking different TSIDs. Dual tuners are capable though. The TSID is very much like a MAC address but in broadcast mode.

Well, see, what I previously posted is not entirely correct, that is how confusing this gets. A little mix of DVB-S there.
I can add that for any given area, there is a separation in channels and coverage. EIRP is also a limit but many places you can get out of area channels via translators. I get channel 6 on the old UHF channel 23, the low end pilot at 524.31 Mhz. and a translator on the old channel 6 with the low end pilot at 82.31 Mhz
6.1 is high definition, 6.2 and 6.3 standard definition. all sub-channels. I get a total of 40 channels with a discone antenna just above the roof.
All 3 channel 6 sub-channels (virtual channels) occupy the 6 Mhz wide channel 23, now obsolete. This is modulated with 8VSB/8PSK (terms interchangeable)
What I see looking at this on my spectrum analyzer, the graph is 10 Mhz wide:

rjenkinsgb. The link you posted is exactly what I was looking for. All the information is there. Everyone read the link it explains it better than I can.