Jak odesílat zprávy, když někdo vypne Internet - Pavel Táborský
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This document outlines how to use amateur (HAM) radio to disseminate messages when the internet is shut down. It recommends using an APRS-capable handheld radio, yagi antenna, and transmitting on VHF bands to send messages via HAM radio satellites like the ISS, which can then be picked up by an international APRS iGate and tweeted via an APRS-Twitter gateway. Alternatively, cheap options like building a yagi antenna from a tape measure and transmitting APRS messages via digipeaters to an iGate are presented. Predicting satellite passes and ensuring infrastructure like digipeaters and an APRS-Twitter gateway are also discussed.
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Jak odesílat zprávy, když někdo vypne Internet - Pavel Táborský
- 1. How to get the message out, when “someone” shuts down the internet Pavel Táborský
- 2. Credentials • ~10+ years in IT, GSM networks before that • HAM License ~1 year • And that’s about it…
- 3. Credits... • Bruce Sutherland, KO4IN • How To Get Your Message Out When Your Government Turns Off The Internet – @DEFCON19
- 4. HAM Radio • Old tech since about 1900 • Usually two skilled operators needed, one at each end • Ionospheric conditions… • (Moon, Aircraft, Satellites)
- 5. 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
- 6. 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) • Twitter
- 7. We will use
- 9. 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
- 10. 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.)
- 11. APRS cont’d
- 12. Infrastructure needed • APRS iGate (preferably in another country) • APRS Digipeater (orbiting) • APRS -> Twitter gateway • Twitter
- 13. ISS Footprint
- 14. 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
- 15. APRS -> twitter gateway • Runs under hamradiotweets.com atm • Interfaces to the aprs.fi (APRS-IS) API to pull the messages • Tweets…
- 16. OSCAR • Stands for Orbital Satellite Carrying Amateur Radio • ISS • PC-SAT (Navy OSCAR-44) • OSCAR status: – http://oscar.dcarr.org/
- 17. Satellite pass prediction • Web Based – http://www.heavens-above.com/ – http://www.n2yo.com/ • Offline – Satscape
- 18. Not foolproof • The system can be jammed • You can be triangulated • Twitter fail whale