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[email protected] · February 20th 13, 09:06 AM posted to uk.transport.london

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