London Banter - View Single Post

Ian Davidson · February 2nd 04, 08:52 AM posted to uk.transport.london

(Damian Skeeles) wrote in message . com...
I love my Oyster card. It's just a bit big...

Has anyone tried cutting down their oyster card to a much smaller
size? Assuming that the smartcard itself takes up a fraction of the
area, that is. After all, this is how the current mini-SIM cards in
mobiles developed from the full credit-card size SIMs...

My main concern is the RF antenna - probably it does run the whole
length / width of the card, and such an operation isn't possible. ISTR
the way these cards work is that the RF energy is enough to power the
card circuitry for the brief period needed to process the transaction;
and this requires a decent-sized antenna.

As to why I want to do this..? Well, it might be quite handy being
able to tape the 'card' to my watch strap, or to my key ring, or
inside my coat sleeve, for example...

The card is a transponder. The RF energy emitted by the reader is
received in the antennae (coil) around the edge of the card. This
powers the card, and the presence of RF at the correct frequency wakes
up the trasmit circuitry and it transmits its coded information. If
you hold the card up close to a very strong light source you should be
able to see the component parts. If you decide to trim your card be
prepared to trash ity and buy a new one!

Damian