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Old 29th Mar 2019, 1:46 pm   #21
julie_m
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Default Re: TalkSport echoes.

NTP doesn't scale well. It's fine if you ask the time occasionally and rely on your own watch in the meantime, but you could not use it for continuous packet streams as required for broadcasting.
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Old 29th Mar 2019, 2:16 pm   #22
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Default Re: TalkSport echoes.

I would think that at least 90% of their listenership are in a good reception area (i.e. outside mush zones) and it really doesn't matter to them, or more near the case doesn't matter to the bean counters.
 
Old 30th Mar 2019, 1:24 pm   #23
broadgage
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Default Re: TalkSport echoes.

During the war, transmitters were synchronised to prevent enemy aircraft using them as a navigation aid.
The enemy could receive the broadcast of course, but could not reliably determine the geographical location of the transmitter, and therefore could not use the signal to assist in navigation.

AFAIK, this practice continued for decades after the war, partly in case of any surprise attack during the cold war.

These days though no one bothers for reasons already given.
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Old 30th Mar 2019, 1:57 pm   #24
Ian - G4JQT
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Default Re: TalkSport echoes.

Quote:
Originally Posted by broadgage View Post
During the war, transmitters were synchronised to prevent enemy aircraft using them as a navigation aid.
The enemy could receive the broadcast of course, but could not reliably determine the geographical location of the transmitter, and therefore could not use the signal to assist in navigation.

AFAIK, this practice continued for decades after the war, partly in case of any surprise attack during the cold war.

These days though no one bothers for reasons already given.
That is correct, but MW synchronised groups (R Five Live, R One, R Three) had to be within 0.05Hz. Apparently audience tests (after the war?) revealed that a 20 second fade - if the listener was between two transmitter sites - was the least-worst option if there was no clear alternative frequency, which there usually was.

I worked at BBC Crowsley Park 1979 - 1996 and taking measurements of BBC MW stations was a daily task. As was as measuring many BBC FM and TV signals as we could detect with out 100ft mast and VHF/UHF antennas.

LW 198 kHz is a frequency standard that we used. It caused a bit of a cuffuffle when it started doing phase mod that first morning sometime in the 1980s, and no one at Droitwich thought to tell us!

I have no idea if the remaining BBC Five Live (or any of the other shared-frequency stations) keep to that specification. I doubt it since they don't even bother to keep the mod in sync, so there would be little point. Those who are or were in UK transmission will be able to describe the current state of play.

(Incidentally, I think some of the North Sea pirate stations had a deliberate offset of about 30Hz. Too high to give grinding fades against a co-channel station, but too low to be audible on most radios.)

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Old 30th Mar 2019, 8:39 pm   #25
G6Tanuki
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Default Re: TalkSport echoes.

Quote:
Originally Posted by julie_m View Post
NTP doesn't scale well. It's fine if you ask the time occasionally and rely on your own watch in the meantime, but you could not use it for continuous packet streams as required for broadcasting.
NTP *does* scale well - for offsets of more than a few milliseconds.

What 'generic' internet digital-data-handling doesn't handle well is the whole diverse-path-routing thing, where time-critical packets can follow multiple routes with different transit-times and so arrive at their destination sometimes several video-frames late - which means they've then become noise [needing to be discarded] rather than signal-to-be-displayed.

Various QoS algorithms can help prioritize realtime traffic over the generic web-browsers, but when you're trying to get HD-video from a studio in Valparaiso to peers in Edinburgh and Berlin it needs _all_ the intervening transit-providers to acknowledge your QoS-tags.
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