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Subelement T8
Modulation modes; amateur satellite operation, operating activities, non-voice communications
Section T8D
Non-voice communications; image data, digital modes, CW, packet, PSK31
Which of the following is an example of a digital communications method?
  • Packet
  • PSK31
  • MFSK
  • Correct Answer
    All of these choices are correct

Digital communications methods are methods that send digital information (encoded in bits, 0 or 1) instead of sending an analog signal, such as voice or video.

The methods listed here are all digital modes:

  • Packet Radio is probably the best known digital mode which can be thought of as using a modem over a radio to allow computers to exchange data

  • JT65 is a digital protocol developed for amateur radio communication with extremely weak signals. It was designed by Joe Taylor, K1JT, to optimize Earth-Moon-Earth (EME) contacts on the VHF bands. The "65" refers to the 65 tones the protocol uses.

  • PSK31 is short for Phase Shift Keying, 31 Baud and is more of system for chat over radio; it allows realtime keyboard to keyboard informal chat between operators.

  • MFSK is short for Multiple frequency-shift keying and is a variation of FSK, a method used by some packet radio systems.

  • IEEE 802.11 is a set of specifications for implementing wireless local area network (WLAN) computer communication in the 900 MHz and 2.4, 3.6, 5, and 60 GHz frequency bands.

Last edited by mk2019. Register to edit

Tags: digital modes

What does the term APRS mean?
  • Correct Answer
    Automatic Position Reporting System
  • Associated Public Radio Station
  • Auto Planning Radio Set-up
  • Advanced Polar Radio System

APRS, Automatic Packet Reporting System, is a standard utilizing packet radio and a GPS to send beacons with the location of the unit. There are many things you can do with APRS, but many use it on bicycles to track their progress, on their vehicle to track where it is, etc. There have even been reports of APRS- equipped vehicles being stolen and then quickly tracked down thanks to the APRS unit.

Last edited by kd7bbc. Register to edit

Tags: digital modes definitions

Which of the following is normally used when sending automatic location reports via amateur radio?
  • A connection to the vehicle speedometer
  • A WWV receiver
  • A connection to a broadcast FM sub-carrier receiver
  • Correct Answer
    A Global Positioning System receiver

Automatic location reports need to know the location to automatically report; thus, they use a GPS just like anything else would =]

If you think about this one, it couldn't be the speedometer anyway; that would only tell you how fast you are going. (also APRS, Automatic Position Reporting System, can be used when biking, driving, walking, etc all just as easily as the other). The other two options are just random things thrown in hoping you won't know what they are so you'll guess wrong. Nearly everyone knows what a GPS is, so this shouldn't be hard to remember.

Last edited by bdengle32@yahoo.com. Register to edit

Tags: digital modes

What type of transmission is indicated by the term NTSC?
  • A Normal Transmission mode in Static Circuit
  • A special mode for earth satellite uplink
  • Correct Answer
    An analog fast scan color TV signal
  • A frame compression scheme for TV signals

NTSC is the name of the standard used to encode colors in an analog fast scan color TV signal.

If you ask a broadcast engineer, NTSC stands for Never The Same Color, because his job is to keep all the cameras looking the same. Now that TV is in the Digital Age the only people you see using the NTSC broadcast standard are Amateur Radio Operators.

Actually, NTSC stands for National Television Systems Committee. They created the rules that governed what the broadcast signal would be electronically so every TV would be able to display the correct picture

Last edited by gusgus45. Register to edit

Tags: amateur television (ATV)

Which of the following emission modes may be used by a Technician Class operator between 219 and 220 MHz?
  • Spread spectrum
  • Correct Answer
    Data
  • SSB voice
  • Fast-scan television

Whenever there is a part of the band that is reserved for Data it is generally the lowest part, and so it makes sense that the range at the bottom of the 220 MHz range would be for data. In point of fact, all non-data frequencies allowed to ham operators in the 1.25 meter band (222 MHz) are from 222.0 to 225.0 MHz, and that block allows phone and image.

219 to 220MHz is for fixed digital message forwarding systems only.

See the ARRL Frequency Chart for a handy one-page reference to band privileges.

Last edited by parraalexis30. Register to edit

Tags: memorizing frequencies digital modes

What does the abbreviation PSK mean?
  • Pulse Shift Keying
  • Correct Answer
    Phase Shift Keying
  • Packet Short Keying
  • Phased Slide Keying

Phase Shift Keying is a method for digitally transmitting data (with a computer of some sort) by varying (keying) the phase of the signal.

Phase refers to where you are in the cycle -- the peaks and valleys of the sine wave

Last edited by kd7bbc. Register to edit

Tags: digital modes definitions

What is PSK31?
  • A high-rate data transmission mode
  • A method of reducing noise interference to FM signals
  • A method of compressing digital television signal
  • Correct Answer
    A low-rate data transmission mode

PSK31 stands for Phase Shift Keying, 31 baud. PSK31 is one of the simplest data modes available; to someone listening, it sounds almost like an electronic whistle, but in actuality it alternates between two phases (hence the name). PSK31 is a fairly slow (low-rate) digital mode and is used mostly for information text chat between two amateur radio operators.

Think of a slow instant messaging system that runs over the radio.

Last edited by bdengle32@yahoo.com. Register to edit

Tags: definitions digital modes

Which of the following may be included in packet transmissions?
  • A check sum which permits error detection
  • A header which contains the call sign of the station to which the information is being sent
  • Automatic repeat request in case of error
  • Correct Answer
    All of these choices are correct

A checksum is an error detection method used by many data transmission types including packet radio. Basically all bytes in the message are added (summed) up and sent as a "checksum". The receiving station repeates this process and "checks" the result against the checksum it received from the sending station.

If the checksum fails (the sums don't match) then an automatic repeat request is sent.

Since packet radio is a form of amateur radio communications the destination station is generally identified at least by call sign, so that information is often included in the header as well.

Last edited by bdengle32@yahoo.com. Register to edit

Tags: digital modes

What code is used when sending CW in the amateur bands?
  • Baudot
  • Hamming
  • Correct Answer
    International Morse
  • Gray

CW stands for "Continuous Wave", which is a sine wave: an electromagnetic wave of constant amplitude and frequency.

This wave can be interrupted, creating an "off" state. The on and off states can be used to transmit Morse code.

The original version of Morse code developed by Samuel Morse is often referred to as Railroad Morse code or American Morse code—American because the rest of the world adopted International Morse. Eventually International Morse also replaced Railroad Morse in America, and this is what we use today.

The term CW comes up a lot; whether you remember what CW stands for or not, every amateur radio operator should know that CW means Morse code.

Last edited by rlaska. Register to edit

Tags: morse code

Which of the following can be used to transmit CW in the amateur bands?
  • Straight Key
  • Electronic Keyer
  • Computer Keyboard
  • Correct Answer
    All of these choices are correct

CW is morse code. There are no restrictions on how you send the morse code, as long as it is correct international morse code.

Last edited by kd7bbc. Register to edit

Tags: morse code

What is a "parity" bit?
  • A control code required for automatic position reporting
  • A timing bit used to ensure equal sharing of a frequency
  • Correct Answer
    An extra code element used to detect errors in received data
  • A "triple width" bit used to signal the end of a character

A "parity" bit is an extra bit added to help detect if the data has been changed through transmission errors. For example, in an 8 bit code there may be 7 bits of data and 1 parity bit; if the parity bit is an "odd" parity bit, then it will be 1 if there is an odd number of 1s in the previous 7 bit set, and 0 if there is an even. "Even" parity is the opposite, as you might guess.

The theory is that if there are any errors in the data stream it is unlikely that there would be more than one error in the same 8 bit block, and so if one of the bits gets flipped through transmission error the parity bit will no longer match (i.e. there will be an even number of 1s in the block but the odd parity bit will be 1), indicating that an error has occurred and the data should be requested again.

Last edited by kd7bbc. Register to edit

Tags: digital modes

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