FIRST: I am OTA only, so I have no first hand experience with the cable issues.
Originally Posted by gastrof
Could any of this be of help in trying to somehow correct the situation I posted about, Weather Channel and my Fox affiliate's widescreen channel sharing exactly the same channel number, the Fox one not being tune-able by the timer record process (unless the machine's left on and tuned to that channel)
Now for my theorizing. For OTA, it seems that the scan process with the digital tuner steps through the available physical channel assignments and looks for detectable digital stations. When it finds one, it makes an entry in a table that shows the display channel number it found in the data stream and the physical channel it was tuned to when it found it. I don't think it makes any record of sub-channel information. Someone else has also speculated that, although the poster escapes me, but I had been thinking the same thing for a while. I believe there are both positives and negatives to the approach. It means you cannot delete individual sub-channels, since there is no table to delete them from. This is an issue if using the tuner as an STB, which I very rarely do. It has the advantage that rescans are not required when sub-channels are added or deleted. It had not occurred to me that multiple physical channels could report the same display channel number until the Minnesota Twin Cities situation came up. Apparently the designers did anticipate that possibility, since the scan does find the 2 transmitters and seems to have created mappings for both. However, things are not orderly. I think that the fact that the lower sub-channel numbers were assigned to the transmitter with the higher frequency assignment contributed to the confusion. That would seem to explain why the sub-channel numbers out of sequence when stepping up. First .3&.4 and then .1&.2. I don't know that the designers totally anticipated all the possibilities in this situation. I can think of a trap they could have easily fallen in. When trying to go to the .1 or .2 sub-channel for a scheduled recording, I would expect them to try the first entry in the tables first, which would be the lower frequency transmitter channel. That transmitter provides the .3&.4 sub-channels. If they did not anticipate the out of sequence situation, they may have assumed that there is no .1 or .2 sub-channel. I am not saying they should not have tried the other transmitter, but I have some sympathy for such a mistake. As I said, I didn't even consider the possibility of multiple transmitters sharing a single display channel. I don't think the ATSC standard provide a lot of guidance on the issue.
So now you may wonder where I am going with this. The Twin Cities people seem to be able to reliably schedule recording by using the physical channel number and the desired sub-channel number that is on that physical channel.
I theorize that, in some cases, the cable situation may be similar. In fact, for some, it may be the Twin Cities situation on steroids. I believe that cable channels occupy the same amount of spectrum as an OTA channel. I have seen people reporting large numbers of sub-channels. I would expect a physical channel with 6 or more sub-channels, even SD ones, to be unwatchable. I suspect that when someone reports 10 sub-channels, those sub-channels must be spread over several physical channels. This would create even more chances for confusion, or mistakes. Also the DVDR tuners, can only get mapping information from the examination of the information in the broadcast data stream. A cable box may even be able to to get information from data streams outside the actual channel content. That could allow them to work with PSIP information that is not accurate.
Now to the poster's question. It may be possible to tune the intended station, if you can find out the physical channel used and the sub-channel number used in that data stream. That would allow you to bypass the translation process, like the Twin Cities OTA people can do. I don't know how to get that info, but maybe someone in the local forum that discusses your local cable channels can provide the information. (The cable company could provide the info, but based on what I am seeing posted, I would not hold my breath wating for them to help out a customer trying to use equipment that is not leased from the cable company.) I know that a couple of people in the Denver OTA forum have tuners that allow them to share this sort of info for OTA stations.
There may be problems doing this for cable, that don't occur in OTA. For OTA, if a station uses display 6 and physical 18, like KRMA, I can tune sub-channel 3 as 6-3 or 18-3, as long as display 6 was found by the scan and there was no entry created for display 18 by a scan. I generally don't have to worry that there will have been an 18 found by the scan. There should not be a display 18 in our area. KRMA is the only station that ever had any rights to that number, although they still use their old NTSC analog station number as there display number, as is the standard.
If this were cable, I suspect you could have a situation like display 6 on physical 18, and display 18 on physical 22. If display 18 was in the DVDR table, then you would not be able to tune physical 18 since you would get re-directed to 22. In that case, you would have to manually delete 18 and tune it using 22. But, 22 could also be an active display channel, and you would have to work around that. In the end, you might have to wipe out much or all of the DVDR digital channel list, and schedule almost everything by physical channels and the sub-channel numbers found on them.
I may be all wet on this, and I have no inside information on how cable systems are configured or experience with one, but I thought I would share my theory anyway.