CRAC Bilingual Manual: Digital Communication Modes | 数字通信方式 (48 questions)

Yaesu System Fusion, abbreviated YSF, is a communication mode integrating digital voice and data transmission. Its characteristics are: (Choose all that apply.)

1. Athis mode is widely adopted in amateur radio communication
2. Bit has the capability to communicate via repeater retransmission
3. Cits modulation mode is C4FM
4. Dit uses time-division multiple access (TDMA) to increase bandwidth utilization

The Icom D-STAR System provides a data communication mode, whose characteristics are: (Choose all that apply.)

1. Ait is a digital voice and data transmission mode widely used in amateur radio communication
2. Bit can extend the communication range of D-STAR users via repeaters
3. Cthis mode allows users to communicate with other users via the Internet and D-STAR hotspots
4. DD-STAR supports GPS (global satellite positioning) and position-reporting functions

FreeDV is a digital voice mode. Its characteristics are: (Choose all that apply.)

1. Ait provides amateurs with a narrow-transmission-bandwidth digital voice mode that is fully suitable for HF
2. Bit gives amateurs the possibility to explore digital-communication principles and speech-processing techniques
3. Cunder an open-source license it can be used to develop one’s own amateur radio equipment
4. Dwhen FreeDV communication is conducted using an FM handheld or mobile radio, the audio is especially beautiful

Digital amateur television (DATV) is a mode applying digital audio/video compression coding to real-time image communication. When conducting DATV contacts via a satellite transponder, amateurs generally choose the DVB-S2 protocol; the modulation may be: (Choose all that apply.)

1. AQPSK
2. B8PSK
3. C16APSK
4. D32APSK

When using the DRM protocol for digital slow-scan television (DSSTV) communication, amateurs always tend to transmit the DSSTV baseband (generated within the audio range) via single sideband rather than FM phone. The main reason is:

1. Athe SSB mode fully preserves the DSSTV baseband characteristics, which helps error control in fading channels
2. Btransmitting DSSTV via FM phone adds the threshold effect and therefore increases the signal’s emission bandwidth
3. Ctransmitting DSSTV via FM phone can improve picture quality but cannot raise audio quality
4. Dtransmitting DSSTV via FM phone can improve audio quality but cannot raise picture quality

The class of emission refers to a set of characteristics of an emission designated by means of standard symbols, e.g., the modulation method of the main carrier, the modulating signal, the type of information sent, and other applicable signal characteristics. The class of emission denoting RTTY transmitted by single-sideband voice is:

1. AF2B
2. BA1A
3. CJ3E
4. DG2B

The class of emission refers to a set of characteristics of an emission designated by means of standard symbols, e.g., the modulation method of the main carrier, the modulating signal, the type of information sent, and other applicable signal characteristics. The class of emission denoting PSK31 transmitted by single-sideband voice is:

1. AG2B
2. BA1A
3. CJ3E
4. DF2B

The class of emission refers to a set of characteristics of an emission designated by means of standard symbols, e.g., the modulation method of the main carrier, the modulating signal, the type of information sent, and other applicable signal characteristics. The class of emission denoting RTTY transmitted by FM voice is:

1. AF2B
2. BF3E
3. CJ3E
4. DF3F

The main considerations in choosing different modulation methods for amateur radio communication are: (Choose all that apply.)

1. Athe fidelity of information during transmission
2. Bthe anti-interference capability of the signal
3. Csaving radio spectrum resources as much as possible
4. Dthe frequency stability of the signal

To satisfy the requirement of “technical characteristics of stations” in our Radio Frequency Allocation Regulations of the PRC (《中华人民共和国无线电频率划分规定》) that radio communication should “keep the bandwidth at the minimum value permitted by the technical state and the nature of the service”, amateur radio operators should understand the necessary bandwidth of various communication methods. The factor that determines the necessary bandwidth is:

1. Athe higher the information transmission rate and the greater the system’s noise interference, the wider the necessary bandwidth
2. Bthe greater the transmitter power, the wider the necessary bandwidth
3. Cthe higher the receiver sensitivity, the wider the necessary bandwidth
4. Dthe closer the communication distance, the wider the necessary bandwidth

Which of the following services use data modes for communication? (Choose all that apply.)

1. ARTTY
2. Bwireless local area network (WLAN)
3. CFT8
4. D5G mobile communication

Frequency-shift telegraphy refers to: a frequency-modulation telegraph technique in which the telegraph signal controls the carrier frequency to vary within a predetermined range. Which of the following amateur communications uses frequency-shift telegraphy:

1. ARTTY
2. BCW
3. CPSK31
4. DSSTV

The modulation method of RTTY is:

1. A2FSK
2. B2ASK
3. CBPSK
4. D2QAM

Digital communication often involves the two parameters “symbol rate”, which describes the change of signal states, and “data rate”, which describes the information flow. The communication mode RTTY uses two frequencies, f0 and f1, as symbols to transmit the digits 0 and 1, and the symbol transmission duration is typically 0.02 s. The symbol rate and data rate of RTTY are respectively:

1. A50 baud, 50 bits/second
2. B100 baud, 100 bits/second
3. C50 baud, 100 bits/second
4. D100 baud, 50 bits/second

Digital communication often involves the two parameters “symbol rate”, which describes the change of signal states, and “data rate”, which describes the information flow. The communication mode BPSK31 uses two opposite phase offsets of subcarrier f as symbols to transmit the digits 0 and 1, and the symbol transmission duration is about 32 ms. The symbol rate and data rate of BPSK31 are respectively:

1. A31.25 baud, 31.25 bits/second
2. B100 baud, 100 bits/second
3. C50 baud, 100 bits/second
4. D100 baud, 50 bits/second

Digital communication often involves the two parameters “symbol rate”, which describes the change of signal states, and “data rate”, which describes the information flow. The communication mode MFSK16 uses 16 subcarriers within a 316 Hz bandwidth as symbols to transmit 16 states, and the symbol transmission duration is 64 ms. The symbol rate and data rate of MFSK16 are respectively:

1. A15.625 baud, 62.5 bits/second
2. B15.625 baud, 250 bits/second
3. C15.625 baud, 15.625 bits/second
4. D62.5 baud, 250 bits/second

Digital communication often involves the two parameters “symbol rate”, which describes the change of signal states, and “data rate”, which describes the information flow. The communication mode QPSK31 uses a pair of reverse phases of carrier f that are mutually orthogonal as symbols to transmit the digits 00 to 11, and the symbol transmission duration is about 32 ms. The symbol rate and data rate of QPSK31 are respectively:

1. A31.25 baud, 62.5 bits/second
2. B31.25 baud, 31.25 bits/second
3. C50 baud, 100 bits/second
4. D31.25 baud, 125 bits/second

Some commonly used amateur radio digital communication protocols only support the transmission of 5-bit or 7-bit data bytes, and are therefore unsuitable for transmitting 8-bit-byte binary data files. Among the following modes, the one that can support binary data file transmission is:

1. APACTOR
2. BRTTY
3. CAMTOR
4. DPSK31

Among the error-control techniques in amateur data communication there are two kinds: “forward error correction” and “automatic repeat request”. Forward Error Correction (FEC) means:

1. AThe sender uses a certain algorithm to obtain redundant check data for the message to be sent, encodes it together with the message and transmits it; the receiver checks the received message according to the corresponding algorithm, and if an error is found, attempts to correct it using the redundant data
2. BAfter sending a certain amount of messages, the sender, upon receiving a retransmission request from the receiver or failing to receive the receiver’s acknowledgment for a long time, judges that an error occurred in transmission and begins retransmitting the messages, so that the receiver can correct the received messages
3. CThe receiver sends the message back to the sender after receiving it, and the sender compares and checks it. If an error is found, the erroneous message is retransmitted, thereby removing errors in transmission
4. DThe sender repeatedly sends each group of messages enough times, and the receiver compares them after receiving them, thereby selecting a consistent group. This can eliminate random errors in transmission

Among the error-control techniques in amateur data communication there are two kinds: “forward error correction” and “automatic repeat request”. Automatic Repeat Request (ARQ) means:

1. AAfter sending a certain amount of messages, the sender, upon receiving a retransmission request from the receiver or failing to receive the receiver’s acknowledgment for a long time, judges that an error occurred in transmission and begins retransmitting the messages, so that the receiver can correct the received messages
2. BThe sender uses a certain algorithm to obtain redundant check data for the message to be sent, encodes it together with the message and transmits it; the receiver checks the received message according to the corresponding algorithm, and if an error is found, attempts to correct it using the redundant data
3. CThe receiver sends the message back to the sender after receiving it, and the sender compares and checks it. If an error is found, the erroneous message is retransmitted, thereby removing errors in transmission
4. DThe sender repeatedly sends each group of messages enough times, and the receiver compares them after receiving them, thereby selecting a consistent group. This can eliminate random errors in transmission

The method of conducting RTTY contacts using a personal computer (PC) and an ordinary voice transceiver is:

1. AFSK (audio baseband modulation of digital information) and SSB (frequency translation)
2. BMT63 (audio baseband modulation of digital information) and SSB (frequency translation)
3. CDRM (audio baseband modulation of digital information) and SSB (frequency translation)
4. Dusing only SSB modulation

The operating method for conducting PSK31 contacts using a personal computer (PC) and an ordinary voice transceiver is:

1. APSK (audio baseband modulation of digital information) and SSB (frequency shifting)
2. BMFSK16 (audio baseband modulation of digital information) and SSB (frequency shifting)
3. CGMSK (audio baseband modulation of digital information) and SSB (frequency shifting)
4. Donly SSB modulation is used

The operating method for conducting HF PACKET contacts using a personal computer (PC) and an ordinary voice transceiver is:

1. AFSK (audio baseband signal modulation of digital information) and SSB (frequency shifting)
2. BTHROBX2 (audio baseband signal modulation of digital information) and SSB (frequency shifting)
3. CALE1200 (audio baseband signal modulation of digital information) and SSB (frequency shifting)
4. Donly SSB modulation is used

PACKET is an amateur radio communication mode developed by enthusiasts using the AX.25 packet communication protocol. When used for HF, VHF, and satellite communications, the symbol rates typically selected are:

1. A300 baud, 1200 baud, 9600 baud
2. B1200 baud, 9600 baud, 19200 baud
3. C300 baud, 2400 baud, 19200 baud
4. D600 baud, 1200 baud, 2400 baud

In VHF packet communication (PACKET), which modulation mode is most widely used?

1. AFM
2. BSSB
3. CAM
4. DOFDM

APRS signals frequently appear on the 2 m amateur band. Their main purpose is:

1. Ato share geographic-location information among amateur stations while they are mobile
2. Bto transmit high-definition video between amateur stations while mobile
3. Cfor amateur stations to monitor arrangements related to emergency incidents
4. Dfor amateur stations to send each other short text messages using chirp (linear FM) modulation

Compared with binary serial modes such as RTTY and APRS, the method of simultaneously transmitting multiple bits of binary information belongs to parallel communication. Among the following amateur digital modes, those that belong to parallel communication are: (Choose all that apply.)

1. AMFSK16
2. BFT8
3. COlivia
4. DCW

If messages are transmitted at the same information transfer rate, the symbol rate when using MFSK16 is lower than the data rate, whereas the symbol rate when using RTTY equals the data rate. This shows that:

1. AMFSK16 has a longer transmit duration per symbol, improving burst-interference resistance and suiting short-wave DX communication better
2. BRTTY’s real communication capability is definitely stronger, because a higher baud rate is always better in every case
3. Csince the two have the same data rate, the communication effect must be identical
4. Dthis proposition is invalid, because the symbol rate always equals the data rate

According to whether the clocks at the transmitting and receiving ends of serial data communication are kept roughly synchronized through special flags within a limited symbol group or a frame, or kept strictly synchronized while sending each symbol, data communication is divided into “asynchronous” and “synchronous” modes. Which of the following is an example of the asynchronous mode:

1. ARTTY
2. BQPSK31
3. CPACKET
4. DPACTOR-II

According to whether the clocks at the transmitting and receiving ends of serial data communication are kept roughly synchronized through special flags within a limited symbol group or a frame, or kept strictly synchronized while sending each symbol, data communication is divided into “asynchronous” and “synchronous” modes. Which of the following is an example of the synchronous mode: (Choose all that apply.)

1. ABPSK31
2. BAPRS
3. CFT8
4. DRTTY

When performing serial asynchronous digital communication, both sides must set the same baud rate, number of data bits, number of parity bits, and number of stop bits. The most commonly used RTTY setting is:

1. A50 (or 45.45) baud, 5 data bits, N (no parity), 1 stop bit
2. B50 (or 45.45) baud, 8 data bits, 2 parity bits, 3 stop bits
3. C31.25 baud, 7 data bits, 170, 0.3
4. D2295, 2125, 170, 5

RTTY, as often called by amateur radio operators, is also known as frequency-shift telegraphy — a frequency-shift telegraphy technique that uses telegraph signals to control the carrier frequency to vary within a predetermined range. Other amateur communication modes that use frequency-shift telegraphy technology include: (Choose all that apply.)

1. AJT65
2. BMFSK16
3. CFT4
4. DSSTV

International Telegraph Alphabet No. 2 (ITA2) has always played an important role in the amateur radio service. Regarding ITA2 encoding, its common name among amateur radio operators, main use, and coding attributes are, respectively:

1. ABaudot code, used for RTTY, each code contains 5 binary bits and can switch state to extend the character set
2. Ba dedicated code, used for PSK31 communication, composed of variable-length codes, able to express 130 characters
3. Ca byte code, used for PACKET communication such as APRS, each code having 8 binary bits
4. DMorse code, used for CW, composed of variable-length codes, devoted to short and elegant message exchange

What is PSK31?

1. Aa low-speed PSK data communication mode
2. Ba method for improving the SNR of FM signals
3. Ca method for compressing digital audio/video
4. Da high-speed PSK data communication mode

The modulation method of PSK31 is:

1. ABPSK (BPSK31) or QPSK (QPSK31)
2. B8FSK
3. C8ASK
4. D64QAM

What is FT8?

1. Aa low-speed FSK data communication mode suited to low-power and low-SNR environments
2. Ba method for improving the SNR of SSB signals
3. Ca method for digital audio/video communication via a satellite linear transponder
4. Da high-speed FSK data communication mode suited to high-power and high-SNR environments

The modulation method of FT8 is:

1. A8FSK
2. B8ASK
3. C8PSK
4. D8QAM

Regarding the digital communication mode JT65, which of the following descriptions is correct: (Choose all that apply.)

1. Aeven with QRP operation, an amateur can use JT65 to contact very distant stations
2. Bsending one JT65 message takes about 50 seconds; the communication speed is not very high
3. CJT65 is suitable for kilowatt-class amateur stations; otherwise it is hard to reach distant stations
4. DJT65 can send about 50 messages per minute; the communication efficiency is very high

FT8 signals are commonly found on HF and VHF amateur bands. The advantages of this mode are: (Choose all that apply.)

1. Aeven with very low transmit power, the probability of successfully contacting distant amateur stations is high
2. BFT8 can be used to explore tropospheric-duct, meteor-scatter, and tropospheric-scatter propagation
3. Calthough FT8’s transmit bandwidth is only 3 kHz, it still contains a large amount of redundant information
4. DFT8’s symbol rate is about 50 bps and it transmits messages using the 5-unit Baudot code

When answering a station’s FT8 call, how should we use the waterfall display provided by the logging software (e.g., WSJT-X) to select an appropriate transmit frequency?

1. Afind a relatively clear frequency in the waterfall time slot where that station is monitoring
2. Bjust pick any frequency on the waterfall at random
3. Cfind a relatively clear frequency in the waterfall time slot where that station is calling
4. Dselect the frequency the station used to initiate its call

FT4 is a communication mode similar to FT8. Its characteristics are: (Choose all that apply.)

1. AFT4’s message speed is about twice that of FT8, but its bit error rate is slightly higher
2. BFT4’s contact efficiency is roughly comparable to RTTY, but its bandwidth is narrower
3. CFT4 is not suitable for exploring sudden propagation phenomena such as meteor trails
4. DFT4, like FT8, also transmits messages using the 5-unit Baudot code

When preparing for FT8, FT4, or JT65 contacts, we need to feed the audio baseband output of the logging software (e.g., WSJT-X) into the transmitter and route the receiver’s output back to the software through a sound card. Some worthwhile setup tips are: (Choose all that apply.)

1. Acarefully adjust the software’s output level and the transmitter’s input gain to avoid transmitter overload that distorts the signal
2. Bcarefully adjust the receiver’s output level and the software’s input gain to avoid decoding distorted signals
3. Cif the radio supports CAT, use the software to control PTT and operating frequency to reduce the chance of misoperation
4. Dif possible, set up the logging software well to avoid errors caused by manual log entry during contacts

An amateur radio station transmits in FM with an RF output power of 10 W, and its power-supply efficiency is about 80%. If the station transmits continuously for 10 seconds, the average transmit power during this period:

1. Ais about 10 W
2. Bis about 12.5 W
3. Cis about 8 W
4. Dis definitely higher than 10 W

An amateur radio station transmits in CW with a carrier output power of 10 W, and its power-supply efficiency is about 80%. If the station sends telegraphy continuously for 10 seconds, the average transmit power during this period:

1. Ais significantly lower than 10 W
2. Bis about 12.5 W
3. Cis about 10 W
4. Dis about 8 W

An amateur radio station transmits in SSB with a peak output power of 10 W, and its power-supply efficiency is about 80%. If the station speaks continuously for 10 seconds, the average transmit power during this period:

1. Ais significantly lower than 10 W
2. Bis about 12.5 W
3. Cis about 10 W
4. Dis about 8 W

An amateur radio station transmits in SSB with a peak output power of 10 W, and its power-supply efficiency is about 80%. If it sends an FT8 message lasting 12.6 seconds using this mode, the average transmit power during this period:

1. Ais about 10 W
2. Bis significantly lower than 10 W
3. Cis about 12.5 W
4. Dis about 8 W

An amateur radio station transmits in SSB with a peak output power of 10 W, and its power-supply efficiency is about 80%. If it sends a PSK31 message lasting 12.8 seconds using this mode, the average transmit power during this period:

1. Ais about 10 W
2. Bis significantly lower than 10 W
3. Cis about 12.5 W
4. Dis about 8 W

An amateur radio station transmits in SSB with a peak output power of 10 W, and its power-supply efficiency is about 80%. If it sends a 10-second Robot 8 SSTV black-and-white image using this mode, the average transmit power during this period:

1. Ais about 10 W
2. Bis significantly lower than 10 W
3. Cis about 12.5 W
4. Dis about 8 W