DFW Daylight Savings Time Transition and ATSC

Fall 2021

Daylight savings time ends on 7 November which means that stations should begin sending PSIP data to that effect on 8 October. The details on how this process should be managed are in ATSC A/65, Annex A and FCC regulations require that all except low power stations follow the standard.

6 October

Something very odd happened at KXTX overnight. For a couple of hours they dropped the in daylight savings time flag:

KXTX (RF 36)KXTX DST change information

At the same time the time they sent shifted by about 23,600 seconds.

7 October

Rather surprisingly after the poor performance this spring, only one station jumped the gun this morning.

KDTN (RF 29)KDTN DST change information

Followed by three more late in the evening

KFWD (RF 9)KFWD DST change information

KDTX (RF 21)KDTX DST change information

KAZD (RF 31)KAZD DST change information

I don't understand why they would do it at three hours early.

But four isn't a horrible number, I guess.

8 October

This is the day they should be doing this.

KTVT (RF 19)KTVT DST change information

KXAS (RF 24)KXAS DST change information

KDFI (RF 27)KDFI DST change information

KUVN (RF 33)KUVN DST change information

KXTX (RF 36)KXTX DST change information

10 October

Five more on Saturday. A day late isn't much of a problem because nobody provides a months worth of schedule data.

WFAA (RF 8)WFAA DST change information

KERA (RF 14)KERA DST change information

KTXD (RF 23)KTXD DST change information

KPXD (RF 25)KPXD DST change information

KMPX (RF 30)KMPX DST change information

That leaves three stations that have done nothing so far: KTXA, KDAF, and KDFW.

10 October

KTXA joined the party at 8PM last night. Better late than never I guess.

KTXA (RF 18)KTXA DST change information

5 November

A few stations just never bothered to do anything at all or have bad data. Several stations have done nothing but then they didn't have the in DST flag set to begin with. (KODF-RF3, K07AAD-RF7, KHPK-RF10, KBOP-RF20, KNAV-RF22. All low power stations.)

KDAF (RF32) does show in DST status but has left the day of month and hour data at zero. KDFW (RF35) is showing a day of month as 1 and hour as 0. So who knows what they think is going on. They don't have the excuse of being low power stations for failing to follow the standard. Too bad the FCC has never bothered toenforce the time portions of the standard.

7 November

Time to switch to CST was 2AM (DST). The standard says stations should drop the in DST flag and zero out the day of month and hour once the entire market they serve has switched over. Since the DFW market doesn't straddle two time zones, that is precisely 2AM DST.

Three stations got off to a bad start by dropping the day of month and hour data back to zero yesterday at 9PM but leaving DS_status as 1 indicating in DST. Which would cause displayed schedule data to have the wrong times. (The Event Information Tables which have that use UTC time which has to be converted to local time before displaying it.) They had the correct day and hour for the change in their PSIP data so why they did this is a mystery. 9PM CDT does happen to be 2AM UTC but that is just too stupid.

(Time in these plots is in DST.)

KFWD (RF 9)KFWD DST change too soon

KDTX (RF 21)KDTX DST change too soon

KAZD (RF 31)KAZD DST change too soon

They then set the DS_status flag to zero (out of DST) at 2AM.

A couple of low power stations took a different approach. They never bothered to indicate an in DST status or mess with day of month or hour. But at 2AM (DST) they offset the time by 3600 seconds.

KODF (RF 3)KODF time offset

KHPK (RF 10)KHPK time offset

KNAV (RF 22)KNAV time offset

They all changed back a few hours later. (Plotted using "linespoints" so you can see how intermittant KODF is for me.)

A few stations managed to do the change at 2AM DST as required: KERA (RF14), KTXD (RF23), and KPXD (RF25).

A larger group decided to wait till 4AM (DST): KTXA (RF18), KTVT (RF19), KDFI (RF27), KDTN (RF29), KMPX (RF30), KUVN (RF33), and KXTX (RF36).

KXAS (RF24) did it a little after 2AM

At the end all but two stations are showing out of DST. Those ignoring the change are KDAF (RF32) and KDFW (RF35). Both full power stations.


In the end not one station managed to comply with the ATSC specification. Some came close and many messed up in ways that wouldn't cause trouble. You would think that after all this time they could do better. Perhaps they just don't care.


I have been doing this since 2015 and previous versions of this page can be found at the Internet Archive. I have archived the raw data and can provide it on request.

ATSC Monitoring