APRS (Automatic Packet Reporting System) is an amateur-radio based system for realtime communication using digital packets sent over radio links. I present here, an implementation of an APRS iGate using the Raspberry-Pi. An APRS iGate is an Internet gateway that gates packets from the radio/RF side to the APRS-IS on the Internet (and vice-versa). The APRS-IS is an Internet based network that connects APRS networks from all around the world and facilitates APRS applications (like realtime postion reporting of objects overlaid over google maps, see aprs.fi).
The key components of piGate are depicted in the diagram below. The VHF FM radio receives the APRS packets and outputs them in form of short bursts of audio tones (APRS uses audio frequency shift keying modulation at 1200baud, listen to a AFSK1200 packet here). The audio is sent to a sound card connected to the Raspberry-Pi. The software running on the Raspberry-Pi reads the audio signal coming into the sound-card, demodulates the signal, decodes the packet and then sends it to an APRS-IS server over the WiFi link.
The hardware used for the setup:
1. Yaesu FT-270E VHF FM Handheld 2-metreband Transceiver.
2. A 2m vertical dipole antenna (not visible in the picture above)
3. The piGate in an extruded aluminium enclosure
(a) A Raspberry-Pi
(b) A MicroNEXT MN-WD152B WiF USB Adapter with external antenna
(b) Sony Singstar usb adapter (being used as the sound card)
(c) A dual-color LED connected to the GPIO header (to indicate status).
PicoAPRS with GPS receiver (Kit) Photo by WIMO.de
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