Research, development and trades concerning the powerful Proxmark3 device.
Remember; sharing is caring. Bring something back to the community.
"Learn the tools of the trade the hard way." +Fravia
You are not logged in.
Time changes and with it the technology
Proxmark3 @ discord
Users of this forum, please be aware that information stored on this site is not private.
Do LF readers have an anti-collision mechanism for reading several cards at the same time ?
And, can a LF card be read at the same time by two different readers when the card enter both reader antenna's field at the same time ?
I tried the following and I couldn't read the card with both antennas at the same time :
On one side, I have a custom made LF antenna X plugged to my PM3 with the 'HID FSKDEMOD' command running.
On the other side, I have a HID thinline reader.
The thinline reader does not pick up the card ID until I remove the LF antenna X.
When the card ID is being read by the PM3, the thinline is not able to read it at the same time.
Whatever how I place the card (closer to the thinline or not) the LF antenna X seems to be winning the battle...
Should I be able to read the card with both readers at the same time ?
Or it can only be done by alternating between both readers (= by turning the power supply of one of them once ID is read; to let the second one do his job)
Offline
I personally have never heard of any low frequency cards supporting anti-collision. The anti-collision concept requires that some amount of intelligence be present on the card in order to perform the necessary collision tag filtering functions. Smart cards have the necessary processing resources and therefore are usually able to support some form of anti-collision.
Regarding your other question ... Yes, a LF card can "theoretically" be read by two different readers but the conditions have to be extremely right for it to work.
I believe your problem can be attributed to the following three reasons:
1. Your HID Thinline reader generates the 125 Khz carrier signal using about a 10 percent duty cycle. That means that it is only activated for about 100 msec during every 1 second interval. Soon after a credential enters an active 125 Khz RF field it begins transmitting its internal code. If your other reader is not yet activated its reader field or it is not ready to receive the data stream then it will not see a valid start sentinel. Basically both readers need to be somewhat in sync before they can both receive and correctly interpret the data.
2. Credentials extract their clock from the 125 Khz signal. If it is seeing two different carriers that are not in sync then their internal clocking mechanism will be corrupted.
3. The circuitry inside a tag transmits data by modulating a load onto the carrier signal. Since this circuitry is typically current limited it will basically be dividing the load between the two readers. Since the amount of modulation will be significantly smaller the cards either need to be closer to the reader or the reader needs to have a very sensitive receiver circuit.
Last edited by carl55 (2013-09-28 20:10:08)
Offline
Hitag1 does support anti-collision, for more information, check this document
Offline
Massive thank you for those detailed informations !
Offline