CRAC Class B (2025) — Questions 451–460

U0757. The main considerations in choosing different modulation methods for amateur radio communication are: (Choose all that apply.)

业余无线电通信选用不同调制方式的主要考虑因素是：

U0758. 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:

为了满足我国《无线电频率划分规定》“电台的技术特性”关 于无线电通信“把带宽保持在技术状态和该项业务的性质所允 许的最低值上”的要求，业余电台操作者应了解各种通信方式 的必要带宽。决定必要带宽的因素是：

U0759. Which of the following services use data modes for communication? (Choose all that apply.)

以下哪些业务使用数据方式进行通信？

U0760. 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:

频移电报技术（frequency-shift telegraphy）是指：电报信 号控制载波频率在预定的范围之内变化的调频电报技术。下述 业余通信使用的是移频电报技术：

U0761. The modulation method of RTTY is:

RTTY的调制方式为：

U0762. 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:

数字通信经常涉及描述信号状态变化的“符号速率”和描述信 息流量的“数据速率”这两个参数。通信方式RTTY使用f0和f1 共两个频率作为符号来传输数字0和1，并且符号的发送时长通 常是0.02秒。RTTY的符号速率和数据速率分别为：

U0763. 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:

数字通信经常涉及描述信号状态变化的“符号速率”和描述信 息流量的“数据速率”这两个参数。通信方式BPSK31使用副 载波f的两个相反的相位偏移作为符号来传输数字0和1，并且符 号的发送时长约为32毫秒。BPSK31的符号速率和数据速率分 别为：

U0764. 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:

数字通信经常涉及描述信号状态变化的“符号速率”和描述信 息流量的“数据速率”这两个参数。通信方式MFSK16使用 316Hz带宽内的16个副载波作为符号来传输16种状态，并且符 号的发送时长为64毫秒。MFSK16的符号速率和数据速率分别 为：

U0765. 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:

数字通信经常涉及描述信号状态变化的“符号速率”和描述信 息流量的“数据速率”这两个参数。通信方式QPSK31使用载 波f的互为正交的一对反相相位作为符号来传输数字00至11， 并且符号的发送时长约为32毫秒。QPSK31的符号速率和数据 速率分别为：

U0766. 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:

有些常用的业余无线电数字通信协议只支持5位或者7位数据字 节的传送，因而不适合传输8位字节的二进制数据文件。下列方 式中可以支持二进制数据文件传输的是：