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Clive · February 20th 13, 01:13 AM posted to uk.transport.london

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