Circuit Cellar - GIFT

CC-2015-06-Issue 299

Circuit Cellar - GIFT

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CIRCUIT CELLAR • JUNE 2015 #299 6 EDITORS' PICKS COMMUNITY Communications AIS TRANSMISSION DECODING By Peter Baston (Circuit Cellar 215, 2008) To be an effective software, Peter created a system that receives and decodes data transmissions from ships and other vessels via the Universal Automatic Identification System. Built around a Luminary Micro LM3S811 evaluation board, the decoder displays a "virtual" radar screen, showing the position of vessels in the area. Baston writes: "As a ham radio and embedded hardware/software engineer, I have long been interested in decoding off-air data transmissions. From an early interest in radio teletype (RTTY) transmissions, I moved on to DOS programs to decode the data from trunked radio systems and paging systems. When I heard about a new marine data system carrying ships' positions, I just had to have a go at decoding the data! The Universal Automatic Identification System (AIS) is a data system that operates on two frequencies in the marine VHF FM band. Ships, and other fixed installations, make frequent broadcast transmissions that may be received by other vessels in range. The transmissions carry both 'dynamic' information (i.e., position and speed) and 'static' information (i.e., name, call sign, and more). A decoder receiving the transmissions can display a 'virtual' radar screen showing the position of other vessels in the area." These articles and others on topics relating to Communications are available at REMOTE AUDIO CONTROL Build a Longwave AM Radio Receiver By Krzysztof Klimaszewski (Circuit Cellar 222, 2009) Krzysztof constructed a digital direct-conversion receiver for long waves. Tuning is controlled by a USB serial connection with a computer running terminal-emulating software. The LM3S811-based system proves you can build a radio receiver with a few discrete components and computer speakers with amplifiers. Klimaszewski writes: "When first I saw the Luminary Micro ARM Cortex-M3 microcontrollers, I realized that it might be possible to develop a full software- defined radio. I wanted to build a modern radio in a matchbox that was as simple as possible, with as few parts as possible. This led to a receiver with weak performance, but that was acceptable. The main purpose of this project was to prove it is possible to develop a software-defined radio using a microcontroller with simple hardware."

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