Originally Posted by
onehundred80
What I would like to know is if the circuit board inside the fob can be used universally, most posts on this subject say it cannot. If not why not?
Surely that would mean another level of security which would be overkill in my mind, but there again I am not a German engineer making life difficult for the masses.
Is it capable of transmitting and receiving signals at a distance or does it receive only when in close proximity to the halo.
If we would like to fabricate keys from scratch using old circuit boards with new chips, keys and cases we need to know this or we will not be able to do it.
Dammit,Dave. You know this **** better than THAT!
Is it capable of transmitting and receiving signals at a distance or does it receive only when in close proximity to the halo.
Not the
Halo - close proximity to the
antenna, behind the Speedometer/Tachometer.
Its in the service manual diagrams, look under "wiring" then "Connector pinouts".
- The HALO is used to energize and communicate with the RFID chip. (Pins 1 and 2 of C3 on the SKREEM are the 'hot' and 'shield' going to the Halo, shielded coax is used to prevent the signal from radiating outside the ring, more on that below.)
- The rolling code lock/unlock board communicates with the SKREEM with the antenna wire in the harness of the SKREEM. (Pin 6 of C1 [C1 is the main SKREEM connector, that dead-end wire on pin 6 is the antenna.])
Some RF basics here:
The halo is not so much an antenna but a coil.
Antennas are intended to radiate. And the antenna on the SKREEM does that, it also is capable of intercepting signals - and it does that, too. When you press a button, your FOB transmits, the SKREEM hears it and IT transmits back, "rolling the code" in the FOB.
The
"halo" (coil) is intended to radiate RF energy as well, but it is designed to contain that radiation largely in the area inside it's circumference. This is for two reasons:
- We need a considerable amount of energy directed to the RFID chip, we need this because this RF is the ONLY source of power for the RFID chip to use to transmit back. When the RFID chip receives this power, it uses it to generate it's signal with the secret code the SKREEM is looking for. So we contain the RF in that small area it is needed in.
- We do not want the signal from the SKREEM or the response from the RFID chip to be detectable to anyone trying to listen to record the code, that would defeat the purpose of the RFID chip in the first place. So again, we use a coil to contain the signal.
This is why there are two "antennas" - each is designed for a specific purpose.
35 years in RF (radio) here. The things I do not know could fill volumes of books - but I better know RF by now.