An Annual Autumnal Occurrence As Daylight Savings Time Falls Back To Standard
At 2:00 a.m. on Sunday, November 2, most of us will return to Standard Time. Historically, that change has tended to affect mainly AM stations whose nighttime facilities differ from their daytime facilities – since the switch from day-to-night and vice versa is normally dependent on the local time of day, which obviously changes with the return of standard time.
But now DTV operators also have to worry about the time shift, since their PSIP is time-dependent as well. The NAB has helpfully alerted us all that, effective October 3, 2008 (between 12:00 midnight and 12:01 a.m.), DTV operators need to adjust the daylight savings settings in their systems in order to assure technical compliance with Section 73.682(d) of the rules, which in turn requires compliance with, among other things, ATSC A/65C. (The link to ATSC A/65C takes you to the complete 155-page PDF — Annex A of ATSC A/65C, which addresses necessary daylight savings time adjustments, may be found on page 88 of that PDF.)
The reason that action is required on October 3 is that the DST fields in the PSIP change one month before the time change goes into effect. They will change again on November 2, when the time change actually kicks in. The details in the ATSC standard for the change on October 3 are as follows:
When the transition out of daylight savings time is within less than one month, the DS_day_of_month field takes the value day_out, and the DS_hour field takes the value hour_out. The DS_status bit is 1 indicating it is still daylight savings time. (The transition is to occur on the day_out day of the month at hour=hour_out; for example, if the transition were on October 27 at 2 a.m., then day_out=27 and hour_out=2) ‘1’ day_out hour_out