CRAC Class C (2025) — Questions 421–430

U0773. In VHF packet communication (PACKET), which modulation mode is most widely used?

在VHF封包通信（PACKET）中，以下哪种调制模式用得最为 广泛？

U0774. APRS signals frequently appear on the 2 m amateur band. Their main purpose is:

APRS信号经常出现在2米业余波段。其主要用途是：

U0775. 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.)

相比RTTY和APRS等二值串行方式，同时传输多位二进制信息 的方式属于并行通信方式。在下列业余无线电数字方式中，属 于并行通信的有：

U0776. 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:

若以相同的信息传输速率传送消息，则使用MFSK16时的符号 速率低于数据传输速率，而使用RTTY时的符号速率等于数据传 输速率。这说明：

U0777. 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:

根据串行数据通信的收发两端的时钟是在一个有限的符号组或 者一个帧内通过特殊的标志维持大致同步还是在发送每个符号 时都保持严格同步，数据通信分为“异步”和“同步”两种方 式。下列属于异步方式的例子是：

U0778. 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.)

根据串行数据通信的收发两端的时钟是在一个有限的符号组或 者一个帧内通过特殊的标志维持大致同步还是在发送每个符号 时都保持严格同步，数据通信分为“异步”和“同步”两种方 式。下列属于同步方式的例子是：

U0779. 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:

在进行串行异步数字通信时，双方需要设置相同的波特率，数 据位数，校验位数和停止位数。RTTY最常用的设置是：

U0780. 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.)

业余无线电爱好者常说的RTTY也叫移频电报，是利用电报信号 控制载波频率在预定的范围之内变化的一种调频电报技术。使 用移频电报技术的业余通信方式还有：

U0781. 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:

国际2号电报码（ITA2）一直在业余无线电业务中发挥着重要 作用。关于ITA2编码，其在业余无线电爱好者中的常见称呼、 主要用途和编码属性分别是：

U0782. What is PSK31?

什么是PSK31？