Extra Class question of the day: VHF and UHF digital modes; APRS

August 29, 2012 Dan KB6NU

One of the most commonly understood concepts in digital communications is the baud. A baud is not equal to a bit per second, except for very simple systems. Rather, the definition of baud is the number of data symbols transmitted per second. (E2D02) A data symbol may represent multiple bits.

The baud rate is a measure of how fast a digital communications system can transmit data. Under clear communications conditions, 300-baud packet is the digital communication mode that has the fastest data throughput. (E2D09)

In the past ten years or so, we’ve had an explosion of digital modes become available. JT65 is one example. JT65 is a digital mode especially useful for EME communications. (E2D03) JT65 improves EME communications because it can decode signals many dB below the noise floor using FEC.(E2D12) FSK441 is a digital mode especially designed for use for meteor scatter signals. (E2D01)

One of the most popular digital modes is the Automatic Packet Reporting System, or APRS. AX.25 is the digital protocol used by APRS. AX.25 is more commonly known as packet radio. (E2D07) Unnumbered Information is the type of packet frame used to transmit APRS beacon data. (E2D08)

APRS stations can be used to help support a public service communications activity. An APRS station with a GPS unit can automatically transmit information to show a mobile station’s position during the event. (E2D10) Latitude and longitude are used by the APRS network to communicate your location. (E2D11) 144.39 MHz is a commonly used 2-meter APRS frequency. (E2D06)

Amateurs that enjoy satellite communications also use digital modes. For example, store-and-forward is a technique normally used by low Earth orbiting digital satellites to relay messages around the world. (E2D05) The purpose of digital store-and-forward functions on an Amateur Radio satellite is to store digital messages in the satellite for later download by other stations. (E2D04)

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