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Subelement E2
OPERATING PROCEDURES
Section E2D
Operating methods: VHF and UHF digital modes and procedures; APRS; EME procedures; meteor scatter procedures
Which of the following digital modes is designed for meteor scatter communications?
  • WSPR
  • Correct Answer
    MSK144
  • Hellschreiber
  • APRS

From the MSK144 section of the WSJTX user manual:

Meteor scatter QSOs can be made any time on the VHF bands at distances up to about 2100 km (1300 miles).

APRS is designed for sending packet data, like location, text, or weather data. WSPR is designed for testing propagation. Hellschreiber is for keyboard-to-keyboard messaging.

MSK = meteor scatter!!!! WP4AES

HINT: MSK = Meteor Scatter Kommunications.

Last edited by jgleave. Register to edit

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Which of the following is a good technique for making meteor scatter contacts?
  • 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
  • Correct Answer
    All these choices are correct

Meteor scatter is a technique where radio signals are bounced off the ionized trail left behind a meteor as it passes into and through the atmosphere.

The presence of a meteor at any given time is not readily predictable, so alternating timeslots are often used to give enough time for a meteor trail to appear, while also making sure stations are not all transmitting in the same timeslot.

When a meteor trail does appear, its signal reflecting properties often only last for a few seconds. High-speed CW or digital modes are used to ensure that several complete transmissions can occur during that short time period.

Meteor trails can also be "shimmery," resulting in signals fading in and out, even over the short time required for a high-speed mode to transmit a callsign. Ensuring important data is repeated many times greatly improves the chances of completing a contact.

Last edited by marvsherman419. Register to edit

Tags: arrl chapter 10 arrl module 10b

Which of the following digital modes is especially useful for EME communications?
  • MSK144
  • PACTOR III
  • Olivia
  • Correct Answer
    JT65

JT65 was designed as a digital protocol for extremely weak signals. It is of particular use in Earth-Moon-Earth (EME) communications on the VHF bands. Error-correction and other features allow communication at signal strengths that are well below the audible range.

[Memory aid: In the US's space quest, 1965 was a landmark year: the first spacewalk occurred.]

MSK144 is also a digital mode available in WSJT-X, but it is for meteor scatter communications, not EME.

Last edited by mandie. Register to edit

Tags: arrl chapter 8 arrl module 8c

What technology is used to track, in real time, balloons carrying amateur radio transmitters?
  • Ultrasonics
  • Bandwidth compressed LORAN
  • Correct Answer
    APRS
  • Doppler shift of beacon signals

http://www.aprs.org/

Automatic Packet Reporting System (APRS) is an amateur radio-based system for real time digital communications of information of immediate value in the local area. In addition, all data is ingested into the APRS Internet System (APRS-IS) and distributed globally for immediate access. Shared information contains global coordinates, altitude, speed, heading, text messages, alerts, announcements, and bulletins. The most visible aspect of APRS is its capability of map display. Anyone may place any object or information on the map, and it is distributed to all maps of all users in the local RF network, or to anyone monitoring the area via the Internet. Any station, radio, or object broadcasting GPS coordinates to the APRS system can be automatically tracked over time.

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What is one advantage of the JT65 mode?
  • Uses only a 65 Hz bandwidth
  • Correct Answer
    The ability to decode signals which have a very low signal-to-noise ratio
  • Easily copied by ear if necessary
  • Permits fast-scan TV transmissions over narrow bandwidth

JT65 [...] is intended for extremely weak but slowly varying signals, such as those found on troposcatter or Earth-Moon-Earth (EME, or "moonbounce") paths. It can detect signals several dB underneath the noise floor [...] –Wikipedia

Note that the 65 doesn't have anything to do with the bandwidth, it's because the encoded messages are transmitted using MFSK with 65 tones.

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Which of the following describes a method of establishing EME contacts?
  • Correct Answer
    Time synchronous transmissions alternately from each station
  • Storing and forwarding digital messages
  • Judging optimum transmission times by monitoring beacons reflected from the moon
  • High-speed CW identification to avoid fading

JT65 uses time synchronous transmissions alternating and is commonly used in EME communications.

(This method is also used in FT8, which has become very popular for regular non-EME use.)

Last edited by marvsherman419. Register to edit

Tags: arrl chapter 10 arrl module 10b

What digital protocol is used by APRS?
  • PACTOR
  • 802.11
  • Correct Answer
    AX.25
  • AMTOR

All APRS (Automatic Packet Reporting System) information uses AX.25 UI (Unnumbered Information) frames because each single packet needs to be heard by everyone. When an APRS station broadcasts its location it does not know if it has been heard and does not need a acknowledgement frame. The use of UI frames means that the network is “unreliable” but lost packets are not as critical as in normal packet radio communications.

Hint: APRS and AX.25 both have 4 characters

Last edited by dekker. Register to edit

Tags: arrl chapter 2 arrl module 2b

What type of packet frame is used to transmit APRS beacon data?
  • Correct Answer
    Unnumbered Information
  • Disconnect
  • Acknowledgement
  • Connect

APRS packets transmit data in the AX.25 protocol, the Amateur variant of the X.25 networking protocol. There are a number of AX.25 packet modes, typically designed for communication links, but APRS sends occasional one-off packets.

Connect and Disconnect packet types would be used to establish, create, and end a formal comms link, and an Acknowledgment packet would be used to confirm receipt of another packet.

APRS packets effectively throw packets into the RF spectrum and hope that somebody receives them, so there is no formal communications link. Therefore, the Unnumbered Information packet type is used, which is designed for this one-off kind of data transmission.

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What type of modulation is used for JT65 contacts?
  • Correct Answer
    Multi-tone AFSK
  • PSK
  • RTTY
  • IEEE 802.11

JT65 uses many tones with a slow symbol rate (baud) in order to get a very high level of sensitivity.

Multi-tone FSK (MFSK) modulation is too specialized to be directly supported by the vast majority of transceivers. Instead the modulation is done at audio frequency on a computer and fed into the transceiver in upper sideband (USB) mode to elevate it to radio frequency. This technique is called Audio FSK or AFSK.

Cheat: Modulation is Multi tone, frequency, amplitude etc etc...

Last edited by ironcal67. Register to edit

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How can an APRS station be used to help support a public service communications activity?
  • An APRS station with an emergency medical technician can automatically transmit medical data to the nearest hospital
  • APRS stations with General Personnel Scanners can automatically relay the participant numbers and time as they pass the check points
  • Correct Answer
    An APRS station with a Global Positioning System unit can automatically transmit information to show a mobile station's position during the event
  • All these choices are correct

The primary way APRS (Automatic Packet Reporting System) is used is to transmit position-- either automatically at intervals (this is called "beaconing") or on demand.

This is used recreationally, but it's also useful in public service communications. Volunteers can have their current position automatically shown on a map.

This can make it easy to track race or parade progress, know the position of volunteers roving an event, etc.

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Which of the following data are used by the APRS network to communicate station location?
  • Polar coordinates
  • Time and frequency
  • Radio direction finding spectrum analysis
  • Correct Answer
    Latitude and longitude

Test hint: APRS location has nothing to do with time and frequency or radio direction finding spectrum analysis. You can also rule out polar coordinates because that is used on graphs.

APRS uses latitude and longitude coordinates to indicate location. (See APRS Positions/objects/items on Wikipedia)

Latitude and Longitude are virtual lines running at 90° to each other around the Earth. Latitude lines run horizontally East and West. Longitude lines run vertical North and South. The lines cut up the surface of the Earth into sections. Latitude lines are 69 miles to each degree and longitude lines are 69 miles to each degree as well.

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