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#1 2012-01-16 20:17:23
- adam@algroup.co.uk
- Contributor
- From: UK
- Registered: 2009-05-01
- Posts: 203
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Mystery modulation scheme
Hi all...
I'm playing with a system that's using a modulation scheme that I don't recognise and wondered if anyone's seen it before... It looks almost like manchester, but when you dig a bit deeper it's clear the timings aren't right for that. In manchester you should be able to measure only two pulse widths, one being exactly double the size of the other, but in this case we see long pulses of 1.5 times... The grid here is set to 40 and the large pulse is measuring 60...
If you want to load and play with the data direct, it's here:
http://www.rfidiot.org/proxmark-test.pm3
Cheers!
Adam
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#2 2012-01-16 21:05:54
- rule
- Member
- Registered: 2008-05-21
- Posts: 417
Re: Mystery modulation scheme
Hey Adam,
Can you give some more info, I assume you are looking into LF samples?
You are sure it is not the Binary puls length modulation (BPLM) used on the reader side of the hitag protocols?
This one has a 100% ASK modulation where the 'one' is 1.5 times the length of a 'zero'.
If you want more details about this, you know how too contact me 
Cheers,
Roel
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#3 2012-01-16 21:24:15
- adam@algroup.co.uk
- Contributor
- From: UK
- Registered: 2009-05-01
- Posts: 203
- Website
Re: Mystery modulation scheme
OK, cards on the table... It's an RF system, not RFID/NFC, but I loaded the trace into PM3 because it's a nice environment to play with such things... 
I've tried decoding it as per your suggestion, but no joy... Any other ideas?
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#5 2012-01-16 22:48:43
- adam@algroup.co.uk
- Contributor
- From: UK
- Registered: 2009-05-01
- Posts: 203
- Website
Re: Mystery modulation scheme
Hmmm... Yep, I thought it might be some kind of PSK, but haven't tried that yet... Trying it now, thanks!
Last edited by adam@algroup.co.uk (2012-01-16 23:14:35)
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#6 2012-01-17 10:06:30
- adam@algroup.co.uk
- Contributor
- From: UK
- Registered: 2009-05-01
- Posts: 203
- Website
Re: Mystery modulation scheme
OK, for those that are interested, it turned out it *was* manchester, just with strange timings!
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#7 2012-01-17 11:51:27
- moebius
- Contributor
- Registered: 2011-03-10
- Posts: 206
Re: Mystery modulation scheme
Sielox tags?
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