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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 especially designed for use for meteor scatter signals?
  • WSPR
  • FSK441
  • Hellschreiber
  • APRS

FSK441, introduced in 2001, is designed to support communication using streaks of radio-reflecting ions created in the ionosphere by the trails of meteors entering the Earth's atmosphere.

The bursts of signal created by such trails are commonly referred to as “pings”, due to their characteristic sound. Such pings may be as short as a tenth of a second and carry enough information to complete at least one stage of a contact.

FSK441 employs multi-frequency shift keying using four tones, at a data rate of 441 baud. Because of the choice of character codes in the protocol, it is self-synchronizing and does not require an explicit synchronization tone. FSK441 is generally used on the 2-meter and 70-centimeter amateur bands.

Contacts may be made at almost any time (that is, a meteor shower is not required to be in progress) at distances of up to 1400 miles (2250 km).

Silly hint: Think of a shooting meteor sounding like "fffiiiisssk!"

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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 high speed CW or digital modes
  • Short transmission with rapidly repeated call signs and signal reports
  • All of 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 given 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.

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Which of the following digital modes is especially useful for EME communications?
  • FSK441
  • PACTOR III
  • Olivia
  • 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.]

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What is the purpose of digital store-and-forward functions on an Amateur Radio satellite?
  • To upload operational software for the transponder
  • To delay download of telemetry between satellites
  • To store digital messages in the satellite for later download by other stations
  • To relay messages between satellites

With a satellite in low earth orbit, the transmit and receive stations may not have a line of sight path to the satellite at the same time. Store and forward allows the transmission to be stored for a while until the receiving station can be “seen” by the satellite

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Tags: arrl chapter 2 arrl module 2b

Which of the following techniques is normally used by low Earth orbiting digital satellites to relay messages around the world?
  • Digipeating
  • Store-and-forward
  • Multi-satellite relaying
  • Node hopping

Store-and-forward means the message is stored and later sent when the satellite is in contact with the appropriate ground station.

Because low-earth satellites can only see a relatively small portion of the earth at once, instantly repeating the message (digipeating) is not a practical method to convey messages long distances.

Unfortunately, there is presently no large network of amateur LEO satellites that would allow instant relaying of messages between multiple satellites.

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Tags: arrl chapter 2 arrl module 2b

Which of the following describes a method of establishing EME contacts?
  • 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.

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

All APRS information uses AX.25 UI 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.

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Tags: arrl chapter 2 arrl module 2b

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

Unnumbered Information is the type of packet frame used to transmit APRS beacon data.

Hint: data = information

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Tags: arrl chapter 2 arrl module 2b

Which of these digital modes has the fastest data throughput under clear communication conditions?
  • AMTOR
  • 170 Hz shift, 45 baud RTTY
  • PSK31
  • 300 baud packet

Biggest number wins, unsurprisingly.

Each mode lists its baud rate (45, 31, 300), other than AMTOR which is 100 baud. And all four modes have 1 bit per symbol which means that is also the bit rate. More bits per second = faster data throughput.

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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
  • An APRS station with a GPS unit can automatically transmit information to show a mobile station's position during the event
  • All of these choices are correct

The primary way APRS 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 your location?
  • Polar coordinates
  • Time and frequency
  • Radio direction finding spectrum analysis
  • Latitude and longitude

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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How does JT65 improve EME communications?
  • It can decode signals many dB below the noise floor using FEC
  • It controls the receiver to track Doppler shift
  • It supplies signals to guide the antenna to track the Moon
  • All of these choices are correct

Earth-Moon-Earth communications involve extremely long paths with extremely weak signals. High amounts of forward error correction (FEC) and narrow signals allow JT65 to punch through despite being potentially too faint to even hear by ear.

[STUDY AID: We were FLOORED when man walked on the moon. --- Only one answer has the word floor in it.]

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

JT65 uses many tones with a slow symbol rate (baud rate) 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.

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What is one advantage of using JT65 coding?
  • Uses only a 65 Hz bandwidth
  • 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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