In the past ten years or so, the number of digital modes has just exploded. JT65 is one example. The type of modulation used for JT65 contacts is multi-tone AFSK. One advantage of using JT65 coding is the ability to decode signals which have a very low signal to noise ratio.
JT65 is a digital mode especially useful for EME communications. One of the reasons that JT65 is such an effective method of establishing EME contacts is because it uses time synchronous transmissions alternately from each station.
QUESTION: What type of modulation is used for JT65 contacts? (E2D09)
ANSWER: Multi-tone AFSK
QUESTION: What is one advantage of the JT65 mode? (E2D05)
ANSWER: The ability to decode signals which have a very low signal-to-noise ratio
QUESTION: Which of the following digital modes is especially useful for EME communications? (E2D03)
ANSWER: JT65
QUESTION: Which of the following describes a method of establishing EME contacts? (E2D06)
ANSWER: Time synchronous transmissions alternately from each station
APRS
One of the most popular digital modes is the Automatic Packet Reporting System, or APRS. Most APRS operation takes place on the 2 m band around 144.39 MHz.
AX.25 is the digital protocol used by APRS. AX.25 is more commonly known as packet radio. Stations transmit APRS beacon data using unnumbered information packet frames.
APRS stations are often 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. Latitude and longitude are used by the APRS network to communicate your location.
APRS is also used to track high-altitude balloons. The teams monitor the APRS transmissions to determine the altitude that the balloon reaches and to locate the payload once the balloon bursts and the payload falls to Earth.
QUESTION: What digital protocol is used by APRS? (E2D07)
ANSWER: AX.25
QUESTION: What type of packet frame is used to transmit APRS beacon data? (E2D08)
ANSWER: Unnumbered Information
QUESTION: How can an APRS station be used to help support a public service communications activity? (E2D10)
ANSWER: An APRS station with a Global Positioning System unit can automatically transmit information to show a mobile station’s position during the event
QUESTION: Which of the following data are used by the APRS network to communicate station location? (E2D11)
ANSWER: Latitude and longitude
QUESTION: What technology is used to track, in real time, balloons carrying amateur radio transmitters? (E2D04)
ANSWER: APRS
Meteor scatter
Digital modes can also be used to make meteor scatter contacts. MSK144 is a digital mode especially designed for use for meteor scatter signals. Good techniques for making meteor scatter contacts include 15-second timed transmission sequences with stations alternating based on location, se of high speed CW or digital modes, short transmissions with rapidly repeated call signs and signal reports.
QUESTION: Which of the following digital modes is designed for meteor scatter communications? (E2D01)
ANSWER: MSK144
QUESTION: Which of the following is a good technique for making meteor scatter contacts? (E2D02)
ANSWER: All these choices are correct
- 15-second timed transmission sequences with stations alternating based on location
- Use of special digital modes
- Short transmissions with rapidly repeated call signs and signal reports