In MythTV when you tune to a digital ATSC OTA channel with the on-screen display active you see the channel number, its name, the program title, the signal strength, the BER of the station (error rate in the signal), the SNR (signal to noise ratio) and a series of code letters in upper and lower case that have meaning for diagnosing problems. If the code letters are upper case that means things are good, lower case means that there is a problem, and an underscore means no data.
What tipped me off to Global's missing MGT data is that CBUT-DT (CBC) and CIVT-DT (CTV) both show "LAMGV
", while CHAN-DT shows "LAM_V
", so I looked it up and the missing G means that there is no MGT table present but everything else is there. I never saw that before because I could not get CHAN-DT entered by automatic scan so it was impossible to tune to it and see the output. Only after manually entering the station into the database (using PHPMyAdmin) and restarting the mythbackend could I tune the mythfrontend to CHAN-DT to see the on screen guide and read those debug letters.
Here's the official MythTV explanation:
23.22 What do the letters mean when I change channels?
These letters let you know what's going on with the backend as it tries to tune to a channel.
Lower case = seen
Upper Case = seen & good
* l/L = Lock : This could be seen by PVR-250/BTTV users
* a/A = PAT : Any recording transmitted in MPEG
* m/M = PMT : Any recording transmitted in MPEG
* g/G = MGT : ATSC only
* v/V = VCT : ATSC only
You can see in the TSReader output from other digital stations posted earlier in the CHAN-DT 22.1 thread that PAT is the Program Association Table, PMT means Program Map Table(s), and VCT means Virtual Channel Table. CHAN-DT has those just fine, but like Dan says, not having a Master Guide Table is a big problem!