GENERAL CLASS Chapter 6.1~6.6 Digital Modes

Chapter 6 Digital Modes

6.1 Intro to Digital Modes 6.2 Digital Basics 6.3 Character-Based Modes 6.4 Packet-Based Modes 6.5 Receive & Transmit Digital Modes 6.6 Digital Operating Procedures

1 6.1 Introduction to Digital Modes page 6-1

∗ Digital communications modes exchange information using individual characters encoded as digital bits . ∗ “A” using CW is “di dah” ∗ “A” using ASCII is “01000001”

∗ Digital communications consists of two basic steps • Information encoding [FCC – 97.309] • formats

∗ Examples of Digital Communications Modes • RTTY, Packet (VHF/UHF), PSK31, JT-65/JT-9/FT-8/JS-8 …. Keyboard • PACTOR, , …. Email and messaging • DSTAR (ICOM), System Fusion (Yaesu), AOR digital voice, WinDRM, FreeDV …. Voice via digital methods2 6.1 Introduction to Digital Modes page 6-1

∗ Digital nodes are restricted to CW/Data segments of the HF bands • Usually found at the top end of the CW segment • Band plans define where digital modes may be found • Calling frequencies are typically at the lower end of the band and activity moves up with increased activity [G2E04, G2E08] ∗ 20 Meter band examples for digital mode operating frequencies • PSK-31 – 14.070 MHz; JT-65 – 14.076 MHz; JS8Call – 14.078 MHz • RTTY – 14.080 MHz ∗ Digital Modes are limited in the maximum data rates and signal bandwidths [FCC – 97.307] ∗ Information encoding and signal transmission protocols must be defined by FCC rules or be a publicly available method. ∗ Digital recording of Modes – http://www.kb9ukd.com/digital 3 6.1 Band Plan page 6-1

∗ Table 6.1 Digital Signal Band Plan [G2E07]

4 6.1 Digital Mode Overview page 6-2~3

∗ (RTTY ) sound similar to fax machine sound ∗ RTTY pronounced “ritty” is the original mode designed to copied and printed off the air by a mechanical teletype device. CW band above JT-65 and PSK-31 typically. ∗ PSK-31 sound , PSK-63 faster, bad PSK31, ALC and overdriven ∗ Narrow bandwidth <100 Hz ∗ Good for weak signal on HF ∗ Sound card based (external or internal PC card) ∗ PACTOR and WINMOR ∗ G-TOR, forerunner of PACTOR using FSK in short bursts at varying data (100 – 300 ) rate depending on conditions ∗ Packet ∗ VHF/UHF mode ∗ Not tolerant of HF transmission errors from noise and fading ∗ CW sound at 20 wpm (CQ CQ CQ)5 6.1 Digital Mode Overview page 6-2

Winlink System (http://www.winlink.org ) • Email and file transfer • Uses the internet to connect a system of email servers with gateway and mailbox stations around the world on HF, VHF and UHF frequencies [G2E13] • No direct connection to the internet • Provides a means for providing email access where it is not available locally or the internet is not available due to disasters or local outages. • Can act as stand alone mailboxes

6 6.1 Digital Mode Overview page 6-3

∗ Other Digital Modes ∗ G-TOR : forerunner of PACTOR using MFSK in short bursts at varying data (100 – 300 baud) rate depending on conditions ∗ MFSK16 : 16 tones FSK… sounds like whistles in a narrow band ∗ JT65/JT9 : Part of WSJT family of protocols by Joe Taylor, Nobel Laureate, Princeton University. Effective in noisy and unstable band conditions at very low signal levels. [G8C01] ∗ CLOVER : MFSK family of modes developed by HAL communications. Designed for high bit rates on HF by structuring data in blocks and paying careful attention to the transmitted waveform. ∗ ALE (Automatic Link Establishment): Searches through a set of frequencies to find the best frequency to communicate with a desired station. ∗ WSPR : Propagation path experimentation mode similar to JT65.

7 6.2 Digital Basics page 6-4

∗ Definitions ∗ Air Link – the part of the communications system involves radio transmission and reception of signals ∗ Bit – the fundamental unit of data; 0 or 1 representing all or part of a binary number ∗ Bit Rate – the number of digital bits per second sent from one computing system to another ∗ Baud or – the number of symbols per second sent from one computing system to another; also known as ∗ Duty Cycle – the ratio of time that a transmitter is on to the total of on time plus off time ∗ Protocol – the rules that control the method used to exchange data between two systems ∗ Mode – the combination of a protocol with a modulation method

8 6.2 Digital Basics page 6-4~5

∗ Digital Data Encoding ∗ Digital signals include both information and overhead bits to control signal flow and provide error correction ∗ The total count of all information and overhead bits is the bit rate ∗ A is a device which encodes information and translates the bits into audio tones for transmission over the air ∗ Symbol Rate ( Baud Rate ) ∗ Baud rate refers to the number of symbols per second ∗ A symbol is the combination of signal characteristics that make up each distinct state ∗ CW has on symbol as an on or off state of the transmitter ∗ In RTTY there are two tones per symbol of the transmitter ∗ For simple codes such as Baudot or ASCII each symbol is one bit

9 6.2 Digital Basics page 6-4

 Data , 9600 baud transmitter ∗ 2 bits, 19.2 bits/sec (9600 x 2) ∗ 4 bits, 38.4 bits/sec (9600 x 4) ∗ 6 bits, 56.6 bits/sec (9600 x 6)  AX.25 Packet ∗ The AX.25 protocol defines only the packet construction and data flow rules ∗ Data modem (TNC) output (audio tones) use a 1200 baud modem standard ∗ Operating practices according to the band plan determines the modulation method (SSB or FM)  Digital Modulation Modes ∗ On-Off Keying (OOK) for CW or Pulse code Modulation (PCM) ∗ FSK and PSK – Frequency Shift Keying, Phase Shift Keying ∗ I/Q Modulation – two carriers with 90˚ phase difference and vary the amplitude and phase independently 10 6.2 Digital Basics – Modulation page 6-5

 Digital Signal Principles ∗ Symbol rate directly effects the required frequency shift for FSK and the tone spacing for AFSK. The receiver requires higher shift or tone spacing to be able to determine the symbol sent  Frequency Shift Keying (FSK) ∗ Frequency shift keying is a method of digital communication in which the individual bits of data are encoded as tones ∗ The two tones are called a “ mark ” and ” space ”[G8C11] ∗ Space represents a “0” and mark represents a “1” ∗ Direct FSK involves controlling the transmitter VFO directly by the digital signal from the computer [G8A01] ∗ AFSK (audio frequency shift keying) uses two audio tones which modulate the SSB or FM transmitter. AFSK is more convenient but requires careful control of audio level to prevent distortion or interference to nearby stations.  Phase Shift Keying (PSK) ∗ The most common type of phase shift keying is to invert one of the waveforms, shifting its phase by 180 degrees. PSK31 is an example. 11 6-5 6.2 Digital Basics – Modulation page 6-5

Phase Shift Keying (PSK) ∗ Bussing at low rates or noise as bit rate increases ∗ Most common is BPSK which shifts the phase 180˚ from one interval to the next

12 6-5 6.2 Digital Basics – Modulation page 6-5

Which sideband to use in digital modes? ∗ Soundcard digital data mode use USB - PSK31, PSK63, JT65, JT9, FT8, JS8Call and other modes ∗ True FSK modes use LSB - Clover, RTTY, PACKET, AMTOR, PACTOR

13 Review Questions – 6.1 to 6.2

G2E04 20 meter frequencies for digital comm. G2E08 where is 20 meter PSK31 operations found G2E07 where is 80 meter digital communications G2E13 what communication system is used for messages G8C01 digital mode for low signal strength operation G8C11 how are FSK frequencies identified G8A01 how is an FSK signal generated

14 OPERATING PROCEDURES

G2E04

What segment of the 20-meter band is most often used for digital transmissions?

A. 14.000 - 14.050 MHz B. 14.070 - 14.100 MHz C. 14.150 - 14.225 MHz D. 14.275 - 14.350 MHz

15 OPERATING PROCEDURES

G2E08

In what segment of the 20-meter band are most PSK31 operations commonly found?

A. At the bottom of the slow-scan TV segment, near 14.230 MHz B. At the top of the SSB phone segment, near 14.325 MHz C. In the middle of the CW segment, near 14.100 MHz D. Below the RTTY segment, near 14.070 MHz

16 OPERATING PROCEDURES

G2E07

What segment of the 80-meter band is most commonly used for digital transmissions?

A. 3570 – 3600 kHz B. 3500 – 3525 kHz C. 3700 – 3750 kHz D. 3775 – 3825 kHz

17 OPERATING PROCEDURES

G2E13

Which communication system sometimes uses the Internet to transfer messages?

A. Winlink B. RTTY C. ARES D. Skywarn

18 SIGNALS AND EMISSIONS

G8C01

Which of the following digital modes is designed to operate at extremely low signal strength on the HF bands?

A. FSK441 and B. JT9 and JT65 C. Clover D. RTTY

19 SIGNALS AND EMISSIONS

G8C11

How are the two separate frequencies of a Frequency Shift Keyed (FSK) signal identified?

A. Dot and Dash B. On and Off C. High and Low D. Mark and Space

20 SIGNALS AND EMISSIONS

G8A01

How is an FSK signal generated?

A. By keying an FM transmitter with a sub-audible tone B. By changing an oscillator’s frequency directly with a digital control signal C. By using a transceiver’s computer data interface protocol to change frequencies D. By reconfiguring the CW keying input to act as a tone generator

21 6.3 Character Based Modes page 6-6

∗ Modes which transmit individual characters between stations are referred to as keyboard-to keyboard or unstructured modes . ∗ CW ∗ RTTY ∗ MFSK ∗ PSK31

22 6.3 Character Based Modes page 6-6

[G8C04] ∗ Radioteletype (RTTY) ∗ The oldest form of ham radio digital communications (excluding CW) ∗ Based on surplus commercial teletype and modem devices. Adapted to use computer sound cards and modem software today.

23 6.3 Character Based Modes page 6-6

∗ Radioteletype (RTTY) Characteristics ∗ 5 bits = 32 characters, not enough for the entire English alphabet, numerals and ∗ Two special codes added, LTRS and FIGS, to increase the character set to 62 not including the special codes ∗ Modem tones; Mark = 2125 Hz, Space = 2295 Hz for a 170Hz shift ∗ HF Speeds; 60, 75, 100 WPM (45, 56, and 75 baud) ∗ The most common speed on HF is 45 baud using 170 Hz shift [G2E06] ∗ Multiple Frequency Shift Keying (MFSK) ∗ Multiple-frequency shift keying or MFSK uses more than two tones to encode data. ∗ MFSK16 uses 16 separate tones

24 6.3 Character Based Modes page 6-6

∗ Multiple Frequency Shift Keying (MFSK) ∗ Multiple-frequency shift keying or MFSK uses more than two tones to encode data. ∗ MFSK16 uses 16 separate tones spaced 15.25 Hz apart using a 50 Hz CW bandwidth. Highly tolerant to fading and multi path distortion as compared to two tone FSK. ∗ DominoEX is an improved MFSK mode that encodes data using the difference between successive tones. Less sensitive to tuning errors and drift. Data rates range from 4 to 21.5 baud in bandwidths up to 524 Hz. ∗ Olivia is a wider bandwidth MFSK mode that occupies from 125 to 1000 Hz depending on the number of tones used. Useful at very low signal levels and includes forward error correction. ∗ MT63 is composed of 64 tones and uses advanced DSP techniques which enable it to perform well under noisy and fading conditions. 25 6.3 Character Based Modes page 6-7

∗ PSK31 ∗ The most popular PSK mode where 31 is the symbol rate (31.25 baud) [G8C09] ∗ The low rate is sufficient for most typists for keyboard-to keyboard communications. Can support up to 50 WPM under good conditions. ∗ Uses Varicode variable length character encoding which assigns shorter codes to the most common characters just like does. [G8C02] ∗ Upper case letters use longer varicode characters and slow down transmission [G8C08] ∗ PSK63 is a higher speed variation of PSK31 at 63.5 baud. ∗ PSK31 is sent as a single tone , encoding each symbol as reversals of phase at regular intervals. Reversal of phase from one interval to the next represents a “0” and no reversal represents a “1”. Two intervals per symbol. Zeros are26 sent continuously for no data. 6.4 Packet Based Modes page 6-8

∗ Packet refers to the transmission of data in structured groups ∗ Header - [G8C03]  Synchronization  Control and Routing  Error correction and detection ∗ Data – usually ASCII, compressed ∗ Trailer – additional control, status or error detection ∗ Encapsulation is the process of putting data in the packet structure. i.e TCP/IP AX.25 packet. ∗ Error Detection – Cyclic Redundancy Check (CRC) value is calculated based on the data and sent. ACK is returned if there is no error. NAK on error. ∗ FEC – Forward Error Correction adds bits that are used to correct errors at the receiver [G8C10]

27 6.4 Packet Based Modes page 6-8

∗ ARQ Systems ( Automatic Repeat reQuest), ∗ Used in PACTOR mode ∗ A error check mismatch results in a NAK being generated at the receiving station and the protocol requests the packet be resent. [G8C05] ∗ The transmitting station sends until a valid packet is received or a retry time out is reached. [ G8C07, G8C06] ∗ You cannot break in on an ongoing between stations using ARQ mode. [G2E09] ∗ Broadcast mode announces a stations presence without a connection to another station ∗ MON mode lets a station listen and copy the data but without error correction. MON mode allows you to determine if a frequency is in use [G2E02] 28 6.4 Packet Based Modes page 6-9

∗ (AX.25) ∗ Based on ANSI X.25 standards adapted to radio transmission instead of wireline circuits ∗ Used on VHF and UHF FM bands ∗ 1200 or 9600 baud ∗ Limited use on HF because of high susceptibility to noise and fading ∗ PACTOR and WINMOR Evolution ∗ Enhances RTTY protocol error performance (noise and fading) ∗ First modes were AMTOR and G-TOR  Sends data in short bursts with error detection and correction  More reliable but very slow in the presence of noise or interference  PACTOR and WINMOR use microprocessor technology to extend the capability of earlier TOR modes

29 6.4 Packet Based Modes page 6-9

∗ PACTOR ∗ PACTOR-I uses FSK modulation while PACTOR-II, PACTOR-III and PACTOR-4 use more advanced PSK modulation ∗ PACTOR-4 is not legal in the US ∗ WINMOR ∗ Can use PSK or FSK. ∗ The preferred method of HF data transmission for the Winlink e-mail system ( www.winlink.org ) ∗ Both modes employ error detection and an ARQ protocol to insure reliable data transmission. ∗ The most popular HF mode for transmission of large amounts of information.

30 Review Questions – 6.3 to 6.4

 G8C04  G2E06  G8C09  G8C02  G8C03  G8C08  G8C10  G8C12  G8C05  G8C07  G8C06  G2E09  G2E02

31 SIGNALS AND EMISSIONS

G8C04

Which of the following describes ?

A. A 7-bit code with start, stop and parity bits B. A code using error detection and correction C. A 5-bit code with additional start and stop bits D. A code using SELCAL and LISTEN

32 OPERATING PROCEDURES

G2E06

What is the most common frequency shift for RTTY emissions in the amateur HF bands?

A. 85 Hz B. 170 Hz C. 425 Hz D. 850 Hz

33 SIGNALS AND EMISSIONS

G8C09

What does the number 31 represent in "PSK31"?

A. The approximate transmitted symbol rate B. The version of the PSK protocol C. The year in which PSK31 was invented D. The number of characters that can be represented by PSK31

34 SIGNALS AND EMISSIONS

G8C02

How many data bits are sent in a single PSK31 character?

A. The number varies B. 5 C. 7 D. 8

35 SIGNALS AND EMISSIONS

G8C03

What part of a data packet contains the routing and handling information?

A. Directory B. Preamble C. Header D. Footer

36 SIGNALS AND EMISSIONS

G8C08

Which of the following statements is true about PSK31?

A. Upper case letters make the signal stronger B. Upper case letters use longer Varicode signals and thus slow down transmission C. Varicode Error Correction is used to ensure accurate message reception D. Higher power is needed as compared to RTTY for similar error rates

37 SIGNALS AND EMISSIONS

G8C10

How does forward error correction (FEC) allow the receiver to correct errors in received data packets?

A. By controlling transmitter output power for optimum signal strength B. By using the varicode character set C. By transmitting redundant information with the data D. By using a parity bit with each character

38 SIGNALS AND EMISSIONS

G8C12

Which type of code is used for sending characters in a PSK31 signal?

A. Varicode B. Viterbi C. Volumetric D. Binary

39 SIGNALS AND EMISSIONS

G8C05

In the PACTOR protocol, what is meant by an NAK response to a transmitted packet?

A. The receiver is requesting the packet be retransmitted B. The receiver is reporting the packet was received without error C. The receiver is busy decoding the packet D. The entire file has been received correctly

40 SIGNALS AND EMISSIONS

G8C07

How does the receiving station respond to an ARQ data mode packet containing errors?

A. It terminates the contact B. It requests the packet be retransmitted C. It sends the packet back to the transmitting station D. It requests a change in transmitting protocol

41 SIGNALS AND EMISSIONS

G8C06

What action results from a failure to exchange information due to excessive transmission attempts when using PACTOR or WINMOR?

A. The checksum overflows B. The connection is dropped C. Packets will be routed incorrectly D. Encoding reverts to the default character set

42 OPERATING PROCEDURES

G2E09

How do you join a contact between two stations using the PACTOR protocol?

A. Send broadcast packets containing your call sign while in MONITOR mode B. Transmit a steady carrier until the PACTOR protocol times out and disconnects C. Joining an existing contact is not possible, PACTOR connections and limited to two stations D. Send a NAK response continuously so that the sending station has to pause

43 OPERATING PROCEDURES

G2E02

How can a PACTOR modem or controller be used to determine if the channel is in use by other PACTOR stations?

A. Unplug the data connector temporarily and see if the channel-busy indication is turned off B. Put the modem or controller in a mode which allows monitoring communications without a connection C. Transmit UI packets several times nd wait to see if there is a response from anther PACTOR station D. Send the message; “Is this frequency in use?”

44 6.5 Receiving & Transmitting Digital Modes page 6-9

∗ Most digital signal on HF are LSB [G2E01] except for JT65 & JT9 which are USB [G2E05] ∗ Key settings for digital communications [G2E14] ∗ Sideband ∗ Baud rate ∗ Tones ∗ Bandwidth of Digital Modes ∗ Defined by FCC rules [97.3(a)(8)] ∗ As symbol rate increases the [G8B05] required bandwidth increases [G8B10] ∗ Standard is to use SSB voice BW ∗ Tones generated by audio from a PC sound card being input to the TX MIC in 45 6.5 Receiving & Transmitting Digital Modes page 6-10

∗ Staying in Band ∗ Use care when operating near the edge of a digital signal band segment ∗ FSK LSB bandwidth calculation; 18103 kHz carrier – 2295 Hz tone =18100.705 kHz radiated signal ∗ Transmitter Duty Cycle ∗ Most amateur transmitters are not designed to operate at full power for an extended period of time ∗ CW and voice have duty cycles of 40 to 50% and 20 to 25% respectively ∗ Digital signals such as RTTY & PSK31 have 100% duty cycle ∗ ARQ modes have slightly reduced duty cycles ∗ For most digital modes reduce power to about 50% [G8B08] ∗ JT65/JT9 usually are operated at a 15 – 25 W power output 46 6.5 Receiving & Transmitting Digital Modes page 6-10

∗ Digital Mode Signal Quality ∗ Require good signal quality ∗ Can cause adjacent channel interference if not properly setup ∗ RF coupling into the audio between the computer and radio are a common problem ∗ Incorrect audio levels are a common problem and may cause splatter or spurious signals ∗ Digital interfaces to the computer such as USB can eliminate level and RF coupling issues ∗ A distorted signal on the waterfall display will have addition lines on either side of the main signal or look broader than normal a signal. Caused by over modulation from high audio input levels [G2E11] 47 5.2 DIGITAL SOUNDS - review (From Technician Class)

• RTTY • AMTOR • PACTOR • PACKET • PSK31 • JT65 • Oliva Digital Signal Waterfall Examples

JT65

PSK31

49 6.5 Receiving & Transmitting Digital Modes page 6-11

∗ ALC and Digital Modes ∗ Automatic Level Control (ALC) is used to prevent excessive to amplifier inputs or overdriving the TX output amp ∗ ALC and digital signals do not work well together ∗ For digital signals the distortion from ALC gain compression makes signal hard to decode and can create interference just like over modulation does [G4A14] ∗ For digital modes the ALC should be off or adjusted to where there is no meter movement for ALC ∗ Receive levels should also be adjusted to within the prescribed levels for the mode50 and application in use Review Questions – 6.5

G2E01 G2E05 G2E14 G8B10 G8B05 G8B08 G4A14 G2E11

51 Commission Rules

G2E01

Which mode is normally used when sending an RTTY signal via AFSK with an SSB transmitter?

A. USB B. DSB C. CW D. LSB

52 OPERATING PROCEDURES

G2E05

What is the standard sideband used to generate a JT65 or JT9 digital signal when using AFSK in any amateur band?

A. LSB B. USB C. DSB D. SSB

53 OPERATING PROCEDURES

G2E14

What could be wrong if you cannot decode an RTTY or other FSK signal even though it is apparently tuned in properly?

A. The mark and space frequencies may be reversed B. You may have selected the wrong baud rate C. You may be listening on the wrong sideband D. All of these choices are correct

54 SIGNALS AND EMISSIONS

G8B10

What is the relationship between transmitted symbol rate and bandwidth?

A. Symbol rate and bandwidth are not related B. Higher symbol rates require wider bandwidth C. Lower symbol rates require wider bandwidth D. Bandwidth is always half the symbol rate

55 SIGNALS AND EMISSIONS

G8B05

What is the approximate bandwidth of a PACTOR3 signal at maximum data rate?

A. 31.5 Hz B. 500 Hz C. 1800 Hz D. 2300 Hz

56 SIGNALS AND EMISSIONS

G8B08

Why is it important to know the duty cycle of the mode you are using when transmitting?

A. To aid in tuning your transmitter B. Some modes have high duty cycles which could exceed the transmitter's average power rating C. To allow time for the other station to break in during a transmission D. All of these choices are correct

57 AMATEUR RADIO PRACTICES

G4A14

What is likely to happen if a transceiver’s ALC system is not set properly when transmitting AFSK signals with the radio using single sideband mode?

A. ALC will invert the modulation of the AFSK mode B. Improper action of ALC distorts the signal and can cause spurious emissions C. When using digital modes, too much ALC activity can cause the transmitter to overheat D. All of these choices are correct

58 OPERATING PROCEDURES

G2E11

What is indicated on a waterfall display by one or more vertical lines adjacent to a PSK31 signal?

A. Long Path propagation B. Backscatter propagation C. Insufficient modulation D. Overmodulation

59 6.6 Digital Operating Procedures page 6-11

60 6.6 Digital Operating Procedures page 6-12

∗ Gateway and Mailbox Stations ∗ Classified by the FCC as automatically-controlled digital stations [G1E11] ∗ Restricted to certain segment of amateur bands only using RTTY below 220 MHz [G1E13] ∗ Non US stations may be outside of FCC allocations. Must be under local or remote control to contact these stations [G1E03] ∗ The contact starts with a connect message [G2E10]

61 6.6 Digital Operating Procedures page 6-12

∗ Operating Displays ∗ Waterfall Display shows the presence of signal a series of lines. Fig 6.3A • Strength of a signal or noise is represented as the brightness Intensity or color of the line at each frequency. Older lines are at the bottom or right [G2E12] ∗ RTTY audio spectrum is shown in Fig 6.3B. The two vertical lines are the mark and space tones ∗ At the right is a crossed ellipse used for fine tuning, two lines at right angles is the correct tuning 62 6.6 Digital Operating Procedures page 6-12

∗ Third Party Traffic ∗ All FCC rules applying to third-party traffic apply to digital transmissions [G1E12] ∗ This includes information in email, digital images or Web pages transmitted by Amateur Radio ∗ This requirement is what limits internet access via gateway and other services.

63 6.6 Digital Operating Procedures page 6-13

∗ Interfering Signals ∗ Hidden transmitter – where you or another station cannot hear or be heard ∗ Garbled messages may be corrected by the protocol or by the operator. ∗ Results of transmission errors or interference may be as follows: [G2E03]  Failure to connect  Frequent retries or transmission delays  Timeouts or dropped connections ∗ Dealing with interference  It is usually because the other station cannot hear you  Change frequency  Use a directional antenna 64 Review Questions – 6.6

G1E11 G1E03 G1E13 G2E10 G2E12 G1E12 G2E03

65 OPERATING PROCEDURES

G2E11

What is indicated on a waterfall display by one or more vertical lines adjacent to a PSK31 signal?

A. Long Path propagation B. Backscatter propagation C. Insufficient modulation D. Overmodulation

66 Commission Rules

G1E03

What is required to conduct communications with a digital station operating under automatic control outside the automatic control band segments?

A. The station initiating the contact must be under local or remote control B. The interrogating transmission must be made by another automatically controlled station C. No third party traffic maybe be transmitted D. The control operator of the interrogating station must hold an Extra Class license

67 Commission Rules

G1E13

On what bands may automatically controlled stations transmitting RTTY or data emissions communicate with other automatically controlled digital stations?

A. On any band segment where digital operation is permitted B. Anywhere in the non-phone segments of the 10-meter or shorter wavelength bands C. Only in the non-phone Extra Class segments of the bands D. Anywhere in the 1.25-meter or shorter wavelength bands, and in specified segments of the 80-meter through 2-meter bands

68 OPERATING PROCEDURES

G2E10

Which of the following is a way to establish contact with a digital messaging system gateway station?

A. Send an email to the system control operator B. Send QRL in Morse code C. Respond when the station broadcasts its SSID D. Transmit a connect message on the station’s published frequency

69 OPERATING PROCEDURES

G2E12

Which of the following describes a waterfall display?

A. Frequency is horizontal, signal strength is vertical, time is intensity B. Frequency is vertical, signal strength is intensity, time is horizontal C. Frequency is horizontal, signal strength is intensity, time is vertical D. Frequency is vertical, signal strength is horizontal, time is intensity

70 Commission Rules

G1E12

Under what circumstances are messages that are sent via digital modes exempt from Part 97 third party rules that apply to other modes of communication?

A. Under no circumstances B. When messages are encrypted C. When messages are not encrypted D. When under automatic control

71 OPERATING PROCEDURES

G2E03

What symptoms may result from other signals interfering with a PACTOR or WINMOR transmission?

A. Frequent retries or timeouts B. Long pauses in message transmission C. Failure to establish a connection between stations D. All of these choices are correct

72