[time-nuts] TV Signals as a frequency reference

[Trent Piepho]

I wrote a program that would scan the PSIP data from my local stations
and the STT was always quite poor.  Usually several stations had the
GPS-UTC offset that was stale, even a year after a leap second.  It
would be trivial to make an automatic correct STT generator some
online data (NTP, etc.), why this was not part of the software that
generated the PSIP data is a mystery to me.

DST was a mess.  I think this bit from A/65 was confusing:

        When the transition into daylight saving time is between one
day less than one month away and the actual transition the
DS_day_of_month field takes the value day_in, and the DS_hour field
takes the value hour_in. The DS_status bit is 0 indicating it is not
yet daylight saving time.

What exactly does "less than one month away" mean?  Does it mean less
than 31*24 hours away?  Does it mean in the current calendar month?

What happens is you get a STT that says "DST begins on the 11th at
2:00 AM".  They couldn't figure out how to pack the month in 16 bits
so you just get "the 11th", no month.  It's now Feb 12th.  Has DST
started?  Some devices would decide the answer is yes and others no.



On Mon, Apr 2, 2018 at 10:08 AM, Mark Sims <holrum at hotmail.com> wrote:
> I read that there is a requirement that the time data in the PSIP data stream has to be within one second.
>
> I have an over-the-air DVR that would mess up the time and recordings because it was originally not filtering the times the stations broadcast.   They finally modified the DVR firmware to do something like a median filter to throw out the outliers.   A local TV guru beat up on all the local stations with a copy of the FCC rules to get the stations to broadcast the correct time.   And don't me started on the ways the stations still mess up the daylight savings time transitions.  Many are a month, week, or day off.
>
> ---------------
>
>> There is no requirement for us to inject time of any prescribed accuracy
> into the digital stream.
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