[LINK] No cash for phone alert system

Pilcher, Fred Fred.Pilcher at act.gov.au
Thu Feb 19 08:46:58 AEDT 2009


I wrote: 

> The POMs have, and have had for some time, a system that 
> overrides the car radio's "off" button for emergency announcements.

I was wrong.

I asked my Pommie mate about it - his reply was:

"You've remembered that when we were driving along, the traffic news
interrupted CD, radio, or silence. When it interrupted silence, it was
because the radio was on, but set to zero volume (the traffic signal
overrides the volume control).

I believe there are radios where the standby button leaves the tuner
monitoring for an alarm flag (a higher priority than the traffic flag or
the news flag), and will turn the radio from standby to on. Naturally,
if the radio's been turned off with a genuine off switch, ie
de-energising the whole device, rather than turned to standby in the
normal fashion, that can't happen.

Information about how far the alarm signal has been implemented by
broadcasters in the UK is not, as far as I know, in the public domain. I
have gained the impression that as far as the government is concerned,
it has not been seen as something to rely on.

In case it's interesting, here's my synopsis of how the system works in
the case of a traffic announcement. The news feature is similar, and the
alarm one differs in that all or most compatible radios don't allow the
user to deselect it.

Whatever audio source the user's listening to, the tuner circuit is
monitoring the radio signal for an inaudible "TA" data flag in the
signal.

When a broadcaster is about to broadcast a traffic announcement -- or
one about serious disruption to public transport (bit of mission creep
there!) -- an operator presses the TA button in the studio. The TA flag
is then added to their feed to the transmitter, and within about a
second it cascades to be inserted into the signal of every radio station
in the region.

The user's radios, if the TA feature hasn't been turned off by the user,
then interpret the signal as a command to retune at once to the station
that's broadcasting the announcement, and raise the volume to the TA
level. They continue in that state until someone in the broadcasting
station releases the TA button, the TA flag ceases, and their radio
returns to the user's previously chosen source, or to silence, as the
case may be.

Some stations which have a dedicated travel desk have automated the TA
flag: as soon as the travel announcer's mic is opened, the TA flag is
triggered without any further intervention.

Not that it's relevant, but a neat feature of most car radios since,
say, the 1980s, is that as soon as you tune into one station, the radio
downloads from the station's datastream a list of all the other
frequencies that station broadcasts on. So I've been able to drive to
Scotland without once retuning the radio, listening to the same station
on different frequencies as my journey progresses. As soon as the
current signal starts to degrade, the radio scans the others in the
list, picks the best of them, and retunes itself.

If you Google for "committee for warning and informing the public"
you'll find some limited information about other means used in the UK to
distribute essential information in times of grave emergency. The BBC
also has a useful microsite aimed at emergency planning officers
(http://www.bbc.co.uk/connectinginacrisis/)."

Apologies for the misinformation.

Fred 
  
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