3 ms·

Transmitter Fingerprinting

• VLM 12y ago
  How it works is you build the analog parts of your synthesizer using 5% to 20% tolerance parts, because they're cheap and you can. Also FM voice being the modulation scheme that it is, you can get away with keying up the transmitter before the synth totally settles without hurting anything. So the "eh don't worry about it" unique preamble to voice FM VHF transmitters was useful for this technique. This is a historical post and when it was made DDS synth techniques had only been popular in ham radio circles for maybe 10 years, now that its even more popular, I wonder if this technique is still useful. Also some modulation schemes (dstar digital voice, etc) embed your ID in the data stream so its not really possible to key up the repeater without identifying. Finally the popularity of FM repeater operation seems to be declining dramatically among the hams, from multiple 24x7 repeaters in use when I was a kid just on 2M, to it basically being a near dead subset of the hobby. There are now more people checking into the long distance sideband nets on 2M and 6M than you'll hear on 2M FM repeaters... (PS and a sufficiently advanced software defined radio, and it doesn't have to be very advanced, can both record, analyze, and play back accurately enough to impersonate someone using a legacy analog synth. Or generate a signal with randomly varying freq response simulating a different device each time, foiling this technology)
  • BuildTheRobots 12y ago
    > Also some modulation schemes (dstar digital voice, etc) embed your ID in the data stream so its not really possible to key up the repeater without identifying. -I assume this can be easily forged and rotated, though; being able to tie multiple instances of iq0 activity to a single transmitter still has it's uses.
• maqr 12y ago
  I wonder if that kind of fingerprinting would work for wifi transmissions?