15 replies to this topic

[James T Kirk]

Has anyone done a survey yet on DAB+ enjoyment in Brisbane's Clem Jones tunnel or Sydney's Harbour tunnel?

[alanh]

Digital radio still uses electromagnetic radiation which will not travel through the conductive earth.

For a car radio and two way radios for the emergency services to work, the tunnel operator has to install a leaky coaxial cable. This is fed by receivers or transceivers from outside the tunnel.
Some Sydney and Melbourne tunnels do not have leaky coaxial cable instalations so there is no radio reception at all. In the ones which have FM there is an amplifier for each station, AM and FM.

If there is reception it depends on if the tunnel operator has installed a band 3 receiving antenna, a 202 - 209 MHz amplifier to drive the leaky cable.

So James, does the Clem Jones re radiate analog radio and Digital radio or none?

AlanH

Edited by alanh, 10 December 2011 - 12:29 AM.

[MLXXX]

Alanh, from the time of its opening the Clem 7 tunnel (which, as many readers will know, passes under the Brisbane River) provided the local AM and FM broadcast stations. This was a safety measure, such that emergency messages could be used to override the usual broadcasts.

As for DAB+, there was no coverage in the tunnel at the beginning. I haven't taken a DAB+ radio into the Clem 7 in recent times to check, but i am not aware of any announcement DAB+ has been introduced.  

I've located a relevant old post on this:

DAB+guy, on May 17 2010, 11:30 AM, said:

... As regards to tunnel repeaters, my understanding is that this is a far more difficult and costly process than re-broadcasting FM (for example). Suffice to say that due to the difficulties, at this stage tunnel re-broadcasting isn't being given high priority.

Cheers,

DAB+guy (ABC)

[GlennP]

In answer to James's question, I doubt it, as you can't receive it. Pretty sure you'd already know that & it was probably a loaded question?
In answer to Alan's question. Yes the Clem 7 tunnel has a leaky coax & re-broadcasts AM & FM, but not DAB+, all the Sydney tunnels have a leaky coax & do likewise (except for the short ones, couple of hundred meters long or shorter), pretty sure all or most Melbourne tunnels are the same. The reason DAB+ isn't in the tunnels is it's difficult to do (as has been mentioned), & the installation & ongoing re-TX costs can't be validated for possibly 5 listeners per day needing/using it, (even though 1 million people listen to DAB+ digital radio, supposedly).
Also I can't find the info just now, but almost certain (in the Sydney tunnels at least), that there isn't amplifiers for the radio signals, where they just pick up the "off air" radio signals, amplify them & send them down the coax. They actually have special transceivers, that receive the signals, break them down, then from scratch re-transmit them on the same frequency as the original, but where output frequencies can be different to input frequencies if needed or wanted.

[alanh]

GlennP,
The Graham Farmer Freeway tunnel in Perth has separate receivers, which Siemens installed. When new FM stations were started they did not come on in the tunnel straight away. I have not said that the signals are demodulated. Each is filtered, amplified and radiated from the leaky coax. This is obviously to stop intermodulation as is the case in channelised MATV systems

Last time I was in Melbourne there was no radio reception in the tunnel which is just south of the CBD.

AlanH

[James T Kirk]

alanh, on Dec 10 2011, 12:20 PM, said:

I have not said that the signals are demodulated. Each is filtered, amplified and radiated from the leaky coax. This is obviously to stop intermodulation as is the case in channelised MATV systems

Despite the responses from GlennP and MLXXX it appears AlanH still hasn't cottoned on as to why radio reception occurs at all in major tunnels.

James

[GlennP]

alanh, on Dec 10 2011, 01:20 PM, said:

GlennP,
I have not said that the signals are demodulated. Each is filtered, amplified and radiated from the leaky coax. This is obviously to stop intermodulation as is the case in channelised MATV systems

I know, but I have said they are demodulated first then re-modulated & fed into the leaky coax, at least in the Sydney Harbour Tunnel & most other Sydney tunnels. Wish I could find the info, the harbour tunnel has quite an elaborate leaky coax re-broadcast system.

Quote

Last time I was in Melbourne there was no radio reception in the tunnel which is just south of the CBD.

Can't say, I never went through that one when I was there recently.

Quote

AlanH

Edited by GlennP, 10 December 2011 - 01:56 PM.

[MLXXX]

Brisbane's $4.8b "AirportliinkM7" project is expected to be open for public vehicles, for the first time, tonight. Its tunnels will feature (http://www.airportli...l-features.aspx ):

• Radio re-broadcast system to enable tunnel operators to broadcast messages over a vehicle's AM or FM radio band

DAB+ is not mentioned.

Presumably DAB+ will come eventually to major road tunnels in areas serviced by DAB+, perhaps in a few years' time. The mere repeating intact of two or more DAB+ multiplexes would be straightforward.  But... the ability to override the usual DAB+ program material with tunnel emergency messages on each of 15 or so DAB+ stations per multiplex... that would require more sophisticated technology.

I'll take a DAB+ radio with me when trying out the new tunnels, to confirm definitely that DAB+ is not being catered for.

Edited by MLXXX, 25 July 2012 - 02:33 AM.

[Malich]

But surely they could have simply installed a band 3 receiving antenna, a 202 195 - 209 MHz amplifier, and some leaky co-ax?

Note: if you've got this far, you may have missed that I was being facetious ;-)

[MLXXX]

Malich, on 24 July 2012 - 05:31 PM, said:

But surely they could have simply installed a band 3 receiving antenna, a 202 195 - 209 MHz amplifier, and some leaky co-ax?you'v got this far, you may have missed that I was being facetious ;-)

An ultimately installed emergency system might use a simple methodology like that for normal periods but in emergencies switch over instead to two or three DAB+ standalone transmitters cloning the identifying parameters of the usual streams but carrying tunnel emergency audio for each of those streams.

Given the volatility of the number and bitrates of DAB stations in existing multiplexes, the cloning parameters might need to be updated hourly...  ;-)   I don't think there is any emergency channel built in to DAB+ radio protocols. But there may be some other functionality that could be used to force the DAB+ radio to tune to a single emergency stream; simplying the design of a tunnel DAB+ emergency transmitter.

I think what the tunnel operators would want to avoid would be drivers tuning into a radio frequency that couldn't be overridden by an emergency announcement. So if DAB+ could not be provided "safely" in a major tunnel, DAB+ would not be catered for at all; thus forcing drivers to tune to AM or FM.

Edited by MLXXX, 24 July 2012 - 06:09 PM.

[Malich]

Highlight the text in my last comment (including a couple of lines below it), or look carefully at the quoted text in yours ;-)

MLXXX, on 24 July 2012 - 05:47 PM, said:

I think what the tunnel operators would want to avoid would be drivers tuning into a radio frequency that couldn't be overridden by an emergency announcement.

Bingo! Just goes to show that a lowly hobbyist with an interest can see things that escape an experienced radio engineer (even 64-year-old ones with a B.Arts & Dip. E&C.)

Edited by Malich, 24 July 2012 - 07:01 PM.

[MLXXX]

Malich, I must admit my first thought about the post was along those lines, but I decided I'd respond at face value, anyway.  Cheers  :-)

Edited by MLXXX, 24 July 2012 - 10:32 PM.

[MLXXX]

We drove through the full length of the AirportlinkM7 tunnels in the wee hours this morning. (The MLXXX household is not only an early adopter of audio-visual technology!)

DAB+ reception ceased upon entry, and remained off. FM and AM continued seamlessly.

As an unexpected bonus, there was an emergency announcement. A well spoken female voice advised that the exit to Stafford Road was blocked and as a consequence all traffic (heading from the Airport end of the tunnel) would need to continue on to Bowen Hills.

The announcement only occurred once and very possibly was a test only. One moment the car radio was playing classical music (ABC Classic FM), the next it was delivering the warning message, and then straight back to the music. No clicks or pops: very smooth!

The tunnel system was impressive, with well placed signs clearly indicating all entry and exit points.

[MLXXX]

There was an interview on the ABC's Brisbane local radio this morning.  The interviewer asked about digital radio particularly with European model cars being fitted with DAB+. The response was that the tunnel provides AM, FM, mobile phone coverage (Telstra and Optus with Vodaphone to follow shortly) but no DAB+. DAB+ was something that might be looked at in the future [or words to that effect].

[Digital Penetration]

MLXXX, on 24 July 2012 - 05:47 PM, said:

An ultimately installed emergency system might use a simple methodology like that for normal periods but in emergencies switch over instead to two or three DAB+ standalone transmitters cloning the identifying parameters of the usual streams but carrying tunnel emergency audio for each of those streams.

Given the volatility of the number and bitrates of DAB stations in existing multiplexes, the cloning parameters might need to be updated hourly...  ;-)   I don't think there is any emergency channel built in to DAB+ radio protocols. But there may be some other functionality that could be used to force the DAB+ radio to tune to a single emergency stream; simplying the design of a tunnel DAB+ emergency transmitter.

I think what the tunnel operators would want to avoid would be drivers tuning into a radio frequency that couldn't be overridden by an emergency announcement. So if DAB+ could not be provided "safely" in a major tunnel, DAB+ would not be catered for at all; thus forcing drivers to tune to AM or FM.

In their digital_radio_accessibility.pdf document, <http://www.acma.gov....cessibility.pdf> ACMA had this to say about emergency broadcasts (page 10):

"Under the MoU, the radio broadcasters will issue emergency warnings on AM and FM
radio and, if available, provide a simulcast on DAB+ digital radio. The coverage of
DAB+ in Australia is limited to the metropolitan areas of Adelaide, Brisbane,
Melbourne, Perth and Sydney.

The European Telecommunications Standards Institute (ETSI) includes a provision to
provide an emergency warning system in the European standard, EN 300 401-
version 1.4.1-Radio Broadcasting Systems; Dig,7a/Audio Broadcasting (DAB) to
mobile, portable and fixed neceivers.

The DAB+ standard allows for the broadcasting of digital data services such as
paging, traffic management and emergency warnings. ETSI did not develop a new
emergency warning system for DAB but instead embedded a known stable technical
notation.''

Dunno if anyone has ever actually used the possibilities, though.

Edited by Digital Penetration, 25 July 2012 - 11:47 AM.

[MLXXX]

Digital P,
it appears there's already at least one "off the shelf" system available:

DAB Emergency Tunnel System (DETS)

The DETS system has been designed to provide a live or pre recorded announcements to be seamlessly switched over all Eureka 147 based (DAB, DAB+, T-DMB, DMB-A) transmissions in road or rail tunnels to cover situations requiring extra ordinary traffic management, - sometimes known as voice break in (VBI).

Based on our highly successful broadcast system, used by DAB broadcasters around the globe, this modular system allows seamless switching between the terrestrial broadcast feed and the emergency message feed to provide the public, clear and concise instructions, via their receiver products, in the event of an emergency situation occurring.

...

• Seamless transition from terrestrial to emergency services broadcast in one simple operation.
  
• Total (Multiple) multiplex replication.
  
• Simple setup.
  
• Seamless integration into new build or retro-fit.
  
• DAB L-Band, DAB Band III, DAB, DAB+, T-DMB and DMB-A support.
  
• Flexible and scaleable to replicate either part or the whole terrestrial signal.
  
• Automated multiplex reconfiguration following.
  
• Unattended operation.
  
• Long Mean Time Between Failure.
  
• Facilitated intersystem redundancy (Optional).
  
• Modular (Upgradeable) design.
  
• Tailored Service Level agreement

The above appears at http://www.radioscap...r-digital-radio

The bit I've highlighted in red would be the powerful feature needed to cater for the chopping and changing of DAB+ stations that goes on, such as temporary stations for special events.