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How to get the message out, when “someone” shuts down the internet
Pavel Táborský
Credentials
• ~10+ years in IT, GSM networks before that
• HAM License ~1 year
• And that’s about it…
Credits...
• Bruce Sutherland, KO4IN
• How To Get Your Message Out When Your Government Turns Off The Internet
– @DEFCON19
HAM Radio
• Old tech since about 1900
• Usually two skilled operators needed, one at each end
• Ionospheric conditions…
• (Moon, Aircraft, Satellites)
Gear
• Wet dream HF/SSB station
– HF radio 40k+
– Mast + yagi dir antenna array ~100k
– Power amplifier(s) etc.
• Or on Budget:
– Yaesu FT-897 ~20k
– Longwire antena ~the cost of the wire
– Essentially what WW2 operators did
We will use
• HAM radio license…
• APRS capable handheld radio ~5k
• Yagi antenna made of tape measure and PVC pipe ~200
• VHF Band (145.825/144.800)
• HAM radio satellite (OSCAR)
– ISS
– PC-SAT (Navy OSCAR – 44)
We will use
Alternatively going cheap(er)
APRS
• Developed in mid ‘80s by Bob Bruninga(WB4APR)
• Originally position reporting system
• Then Messages and WX reports
• X.25 for HAMs
– 1200baud
– AFSK modulation
• APRS is a retronym of WB4APR
– Automatic Packet/Position Reporting System
APRS cont’d
• The network consists of radio stations operating entirely with broadcasted packets
• Digipeaters retransmit packets with store and forward approach and follow DIGIPATH
• Packets are picked up by internet gateways (iGate) and handed over to the the APRS-IS to plot on a map
• Allows for sending variety of packet types (position, object, telemetry, weather etc.)
APRS cont’d
Infrastructure needed
• APRS iGate (preferably in another country)
• APRS Digipeater (orbiting)
• APRS -> Twitter gateway
ISS Footprint
APRS via Satellite
• Set radio transmit to 145.825
• ARISS on the 1st position in the digipath
• Compose an APRS message to TWITR
• Wait for the satellite to be over the horizon
– And chosen iGate in the footprint
• Send the message
• Message gets digipeated back to ground iGate
• And picked by the APRS-IS network
• Subsequently by the APRS -> twitter gateway
APRS -> twitter gateway
• Runs under hamradiotweets.com atm
• Interfaces to the aprs.fi (APRS-IS) API to pull the messages
• Tweets…
OSCAR
• Stands for Orbital Satellite Carrying Amateur Radio
• ISS
• PC-SAT (Navy OSCAR-44)
• OSCAR status:
– http://oscar.dcarr.org/
Satellite pass prediction
• Web Based
– http://www.heavens-above.com/
– http://www.n2yo.com/
• Offline
– Satscape
Not foolproof
• The system can be jammed
• You can be triangulated
• Twitter fail whale