[tz] CCTF survey on Time and Frequency Metrology - Telecom

Brian Inglis Brian.Inglis at SystematicSw.ab.ca
Wed Jan 27 21:56:44 UTC 2021

On 2021-01-27 12:58, Fred Gleason wrote:
> On Jan 26, 2021, at 19:03, Brian Inglis <Brian.Inglis at SystematicSw.ab.ca 
> <mailto:Brian.Inglis at SystematicSw.ab.ca>> wrote:
>> Digital processing mainly compression/decompression delays in the common 
>> modern broadcast chain results in time announcements, transitions of minutes, 
>> audio "pips", clock tower chimes or bells, varying by eyeball and wristwatch 
>> measurable amounts from accurate time sources.
>> Some articles talk about timing broadcast sources to determine which earlier 
>> "pip" signals the correct time.
>> Apparently coordinating multiple regional sources in e.g. commentaries, 
>> discussions, or now virtual talk shows, requires time code calibration and 
>> compensation, so that discussions can appear natural; more so than many remote 
>> news reports which can show very pronounced delays, probably due to cellular 
>> mobile or wifi sources and internet routes.
>> Satellite links add only up to 250ms each round trip.
>> Many articles lack date stamps so it is difficult to know even if the BBC 
>> still transmits legacy analogue AM or FM with accurate "pips" or if stations 
>> are mainly DAB in the EU and UK.
> It’s not just in the EU or UK. Digital modulation methods in common use on 
> broadcast air chains in the US (both audio and video) can easily add up to 
> several *seconds* of latency per hop. This can be the case even when the final 
> delivery link to the receiver is ‘analog’ —e.g. amplitude modulation (‘AM’) via 
> medium wave. Effectively, all audience-facing time marks on such broadcasts 
> should be treated as being precise only to the nearest minute.


I'm unaware of broadcast network time signals and their accuracy in NA other 
than CA CBC Radio One at 13:00 ET, and NR have disclaimers about those and 
telephone time and talking clocks possibly having one or two ~0.25s satellite 
hops added, which makes them useless:



The telephone and broadcast time data require obsolete Bell 103 modem decoders 
and suffer from unknown telco or shortwave propagation or ionospheric delays and 



Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada

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