Gefreiter Krueger wrote:
I got a cheap door access controller from Hong Kong. The keyfob has to
be placed within 1.5 inches of the keypad for it to be picked up. Is it
possible to make it sensitive enough so that approaching the doorway
with the keyfob in your pocket would unlock the door? (Much like some
cars do). It picks up the fob using a coil of wire round the edge of
the keypad (which is 10cm across). The coil looks like about 100 winds
of thin wire of the same sort used in CRTs. If I made a huge version of
this coil right round the doorway, would the range be increased? Or
would there not be enough power in the chip to transmit over that much
area?

Not a lot you can do without a lot of test equipment and knowledge.
These things are specified for a range of 100mm maximum. There is a
different standard to cover the 100cm units that are possibly used in cars.
1) you need extra power so that sufficient RF power arrives at the tag
to power it up.
2)Tinkering with the coil will de-tune it and will transmit far less
power and reduce the RF sensitivity.