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Lame Signal Jammer


While at the WCTF at Shmoocon 2014, I had configured one of the pi’s to kill off the xmit for the wav files that were playing after each file and the other pi didn’t do that. Guess which one started to drift up the band. Additionally, the characteristics of the signal started to spike in very odd ways, and for a little bit, looked not so different from that of a jammer hence this first very bad idea. DO NOT TRY THIS AT HOME. All measurements are made with a HackRF.

This was done to see if it is possible; yes, it is. I cannot stress as to how illegal this is, so don’t repeat in my mistake. Use this as a warning.

Tools Needed

  1. A Raspberry Pi with pifm loaded. Get pifm here: http://www.icrobotics.co.uk/wiki/index.php/Turning_the_Raspberry_Pi_Into_an_FM_Transmitter
  2. A nice box for your pi: http://www.amazon.com/gp/product/B00CJSOYMG/ref=oh_details_o07_s01_i00?ie=UTF8&psc=1
  3. A respectiful antenna to connect: http://www.amazon.com/gp/product/B0083Y3L2O/ref=oh_details_o00_s00_i01?ie=UTF8&psc=1
  4. The commands:
#install sox and minimodem
apt-get install sox libsox-fmt-all minimodem
#generate some white noise
sox -traw -r48k -es -b16 -c1 -V1 /dev/urandom -twav random.wav
#play it
./pifm random.wav 98.9
#shutdown the x-mit
touch /tmp/empty && /home/pi/pifm /tmp/empty

What’s Happening

A simple demonstration of using the right antenna means you’ll get the job done. I wrote a variation of this script that would jump around a little bit of the center of the frequency band that you wanted, but this thing just outputs so much energy, it easily overpowers commercial FM.

Here is a screenshot of the pi in action:

The station attacked is 98.9 (here in Philadelphia), and there are five things to observe:

  1. Pre and post attack, everything goes back to normal.
  2. The static wavefile just killing everything.
  3. The pi with the transmitter still turned on, but nothing to send; it still overpowers the stations with silence.
  4. The impact that it has to adjacent channels.