There's no obvious leaky feeder cable for the new train control system. Does
it use discrete antennas or is it fed through the rails like the old one?

B2003

On Mon, 11 Feb 2013 12:06:51 +0000
Paul Corfield wrote:
On Mon, 11 Feb 2013 11:48:45 +0000 (UTC), d
wrote:

There's no obvious leaky feeder cable for the new train control system. Does
it use discrete antennas or is it fed through the rails like the old one?

http://www.districtdavesforum.co.uk/...on=display&thr
ad=16068

Interesting. Can't tell from that though whether its fixed block or moving
block. Anyone know?

"The transponder sends a 2.4GHz data signal back to the reader."

2.4Ghz eh? And LU is rolling out wifi into stations. Hmm. What could possibly
go wrong?

B2003

On Mon, 11 Feb 2013 12:38:54 +0000
Paul Corfield wrote:
"The transponder sends a 2.4GHz data signal back to the reader."

2.4Ghz eh? And LU is rolling out wifi into stations. Hmm. What could possibly
go wrong?

I'm not a techie - are you suggesting there is an interference risk?

Depends what frequencies around the 2.4Ghz band they use but if they use
ones on or near the wifi ones then yes. No doubt they used that band because
its license free but I wouldn't have thought you'd have needed a license if
its only ever used underground. I suspect the risk is small but why take it
at all?

B2003

In message , d
wrote:
"The transponder sends a 2.4GHz data signal back to the reader."

2.4Ghz eh? And LU is rolling out wifi into stations. Hmm. What could
possibly
go wrong?

I'm not a techie - are you suggesting there is an interference risk?

Depends what frequencies around the 2.4Ghz band they use but if they use
ones on or near the wifi ones then yes. No doubt they used that band because
its license free but I wouldn't have thought you'd have needed a license if
its only ever used underground. I suspect the risk is small but why take it
at all?

You need a licence (or to be exempt) whether or not you're underground.

Bluetooth and WiFi in the 2.4 GHz band is limited to 10 mW and has other
restrictions on duty cycle and power density. Railway equipment in 2.446
to 2.454 is allowed 500 mW in a narrow channel ( 1.5 MHz). Given that
the application is a train passing straight over the transponder in the
four foot, I suspect that the WiFi signal won't even be noticed.

(That band is Bluetooth channels 44 to 52 inclusive (out of 0 to 78).
WiFi channels 8 and 9 completely cover it, while channels 7 and 10 have
some overlap and 6 and 11 just touch it.)

--
Clive D.W. Feather | Home:
Mobile: +44 7973 377646 | Web: http://www.davros.org
Please reply to the Reply-To address, which is:

In message , Clive D. W. Feather
writes
In message , d
wrote:
"The transponder sends a 2.4GHz data signal back to the reader."
2.4Ghz eh? And LU is rolling out wifi into stations. Hmm. What could
possibly
go wrong?
I'm not a techie - are you suggesting there is an interference risk?
Depends what frequencies around the 2.4Ghz band they use but if they use
ones on or near the wifi ones then yes. No doubt they used that band because
its license free but I wouldn't have thought you'd have needed a license if
its only ever used underground. I suspect the risk is small but why take it
at all?
You need a licence (or to be exempt) whether or not you're underground.
Bluetooth and WiFi in the 2.4 GHz band is limited to 10 mW and has
other restrictions on duty cycle and power density. Railway equipment
in 2.446 to 2.454 is allowed 500 mW in a narrow channel ( 1.5 MHz).
Given that the application is a train passing straight over the
transponder in the four foot, I suspect that the WiFi signal won't even
be noticed.
(That band is Bluetooth channels 44 to 52 inclusive (out of 0 to 78).
WiFi channels 8 and 9 completely cover it, while channels 7 and 10 have
some overlap and 6 and 11 just touch it.)
The Victoria line trains when new had the controlling current through
the running rails. It was about 680Hz for full speed, about 450Hz full
series, about 260Hz to coast and anything less full brake application.
The trains haven't changed, has the signalling system?
--
Clive

On Tue, 19 Feb 2013 20:09:07 +0000
"Clive D. W. Feather" wrote:
In message , d
wrote:
"The transponder sends a 2.4GHz data signal back to the reader."

2.4Ghz eh? And LU is rolling out wifi into stations. Hmm. What could
possibly
go wrong?

I'm not a techie - are you suggesting there is an interference risk?

Depends what frequencies around the 2.4Ghz band they use but if they use
ones on or near the wifi ones then yes. No doubt they used that band because
its license free but I wouldn't have thought you'd have needed a license if
its only ever used underground. I suspect the risk is small but why take it
at all?

You need a licence (or to be exempt) whether or not you're underground.

Bluetooth and WiFi in the 2.4 GHz band is limited to 10 mW and has other
restrictions on duty cycle and power density. Railway equipment in 2.446
to 2.454 is allowed 500 mW in a narrow channel ( 1.5 MHz). Given that
the application is a train passing straight over the transponder in the
four foot, I suspect that the WiFi signal won't even be noticed.

Thats all very well, but whats stopping someone shoving a bluetooth signal
through a linear amp to disrupt the comms? If you think thats a stupid thing
to do , well hackers tend to do stupid things.

Spud

In article ,
wrote:
On Tue, 19 Feb 2013 20:09:07 +0000
"Clive D. W. Feather" wrote:

Bluetooth and WiFi in the 2.4 GHz band is limited to 10 mW and has other
restrictions on duty cycle and power density. Railway equipment in 2.446
to 2.454 is allowed 500 mW in a narrow channel ( 1.5 MHz). Given that
the application is a train passing straight over the transponder in the
four foot, I suspect that the WiFi signal won't even be noticed.

Thats all very well, but whats stopping someone shoving a bluetooth signal
through a linear amp to disrupt the comms? If you think thats a stupid thing
to do , well hackers tend to do stupid things.

There was the case in China recently where repeated disruption to a
2.4GHz metro train control system was blamed on a high number of personal
wireless hubs built into passengers' equipment. This article is a bit
lacking in technical details but gives the outline:
http://english.caijing.com.cn/2012-11-20/112296950.html

Nick
--
"The Internet, a sort of ersatz counterfeit of real life"
-- Janet Street-Porter, BBC2, 19th March 1996

On Wed, 20 Feb 2013 10:18:00 +0000 (UTC)
Nick Leverton wrote:
In article ,
wrote:
On Tue, 19 Feb 2013 20:09:07 +0000
"Clive D. W. Feather" wrote:

Bluetooth and WiFi in the 2.4 GHz band is limited to 10 mW and has other
restrictions on duty cycle and power density. Railway equipment in 2.446
to 2.454 is allowed 500 mW in a narrow channel ( 1.5 MHz). Given that
the application is a train passing straight over the transponder in the
four foot, I suspect that the WiFi signal won't even be noticed.

Thats all very well, but whats stopping someone shoving a bluetooth signal
through a linear amp to disrupt the comms? If you think thats a stupid thing
to do , well hackers tend to do stupid things.

There was the case in China recently where repeated disruption to a
2.4GHz metro train control system was blamed on a high number of personal
wireless hubs built into passengers' equipment. This article is a bit
lacking in technical details but gives the outline:
http://english.caijing.com.cn/2012-11-20/112296950.html

Oh dear. Looks like LU may have saved a few pennies but potentially left
themselves with a serious problem especially if the new system on the Met
also uses 2.4 Ghz because thats mostly above ground. One hacker with a grudge
could probably bring the entire line to a halt. Or even worse, if they can
duplicate the comms protocol and override the real signal then they could
potentially cause a crash.

Spud

In message , Steve Fitzgerald
] writes
In message , Clive
writes
The trains haven't changed, has the signalling system?
I think you might find they have!
The driver also used to be able to speak to control in a system that ran
through the juice rails. So what is the system now and when did it
change?
--
Clive

Clive wrote:
In message , Steve Fitzgerald ] writes
In message , Clive
writes
The trains haven't changed, has the signalling system?
I think you might find they have!
The driver also used to be able to speak to control in a system that ran
through the juice rails. So what is the system now and when did it change?

Didn't he use the usual wires along the tunnel wall?