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

Garrett Wollman wollman at csail.mit.edu
Thu Jan 28 19:15:21 UTC 2021

<<On Wed, 27 Jan 2021 15:02:30 -0800, Paul Eggert <eggert at cs.ucla.edu> said:

> And as far as I know, KNX's audio time signal is no more accurate now 
> than it was in the 1990s.

Most CBS owned-and-operated radio stations installed "HD Radio", which
requires an eight-second delay in the analog audio to match the
compression delays on the digital side.  (CBS Radio's then national VP
of engineering, Glynn Walden, was heavily involved in the creation and
promotion of the "HD Radio" system.)  Receivers may add additional
decoding delays so long as they delay analog audio an equal amount.
(This allows for "seamless" cross-fading between the analog and
digital signals at the fringes of the digital coverage area.)  The
encoding delay for "HD2" and other low-bandwidth subchannels is even
longer, about 30 seconds (there's no blend-to-analog issue there, just
the encoder).

Even before HD Radio, CBS affiliates that carried the network news at
the top of the hour would normally take the "bong" from the network
feed, via satellite.  However, CBS stations running a talk format
would not normally dump the profanity delay for the news, so the
network "bong" would be delayed another seven to fifteen seconds.
Some talk stations chose to insert their own top-hour tone after the
profanity delay, often at the transmitter.

(Aside: When Westinghouse bought CBS, this combined Westinghouse's
all-news stations with CBS's all-news stations in several major
markets, including Los Angeles; other than New York, the weaker of the
two stations ended up changing formats.  But after Westinghouse
changed its corporate name to "CBS", this had the effect that "CBS"
owned a number of radio stations that were not affiliates of the CBS
Radio Network -- the former Group W stations were primarily ABC
Information Network affiliates if they had any network at all.  ABC-I
didn't broadcast a top-hour time signal, so those stations, like WBZ
in Boston, already had their own local top-hour beeps if they wanted.
WTIC in Hartford, which wasn't a Westinghouse station but did later
become part of CBS Radio, famously kept its V-for-Victory Morse code
interval signal from World War II.  A few years back, CBS spun off its
radio unit to Entercom, but kept the CBS Radio News network under the
new name "CBS News Radio".)


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