CRAC Class B (2025) — Questions 431–440
U0737. In the amateur radio service, the speed of Morse code signals is often measured in WPM; the method of measurement is:
在业余无线电业务中，莫尔斯电码的信号速度经常用WPM作为 单位，其计量方法为：
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A standard word ("PARIS", 50 dot-units) defines the WPM scale, so WPM = (number of gap-free dots per minute) ÷ 50 (A). Dividing by 60 (D) would be a different (PARIS-less) scale; WPM is not simply English or Chinese characters per minute.
U0738. In the amateur radio service, the signal-timing standard used when calculating the WPM speed of Morse code (with the duration of one 'dot' signal as the reference) is: dot signal, dash signal, intra-character dot-dash spacing, inter-character spacing, and inter-word (group) spacing are respectively:
在业余无线电业务中，计算莫尔斯电码的WPM速度时采用的信 号时值标准（以一个“点”信号的时间为比较基准）为，点信 号、划信号、字符内点划信号的间隔、字符之间的间隔、单词 （组）之间的间隔分别为：
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The standard Morse timing, in units of one dot, is: dot = 1, dash = 3, intra-character gap = 1, inter-character gap = 3, inter- word gap = 7 (A). This is the universal timing that defines the code's rhythm.
U0739. The necessary emission bandwidth of a CW signal can be calculated using the formula Bn =
计算CW信号的必要发射带宽可以使用公式Bn=B×K。其中，B 为波特率。如果已知拍发电码的WPM值，则B可以计算为：
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Because one PARIS word = 50 dot-units and one dot = 1 bit at the keying rate, the baud rate B (bits/s) equals (WPM × 50)/60 = WPM / 1.2. Hence B = WPM/1.2 (A). The other arithmetic forms do not follow from the PARIS timing.
U0740. The necessary emission bandwidth of a CW signal can be calculated using the formula Bn =
计算CW信号的必要发射带宽可以使用公式Bn=B×K。其中， 常数K描述电码符号翻转时CW射频信号的边带滚降特性。K的 取值原则是：
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K is a dimensionless rolloff factor: on fading HF channels a wider K=5 is used to ensure copy, while on non-fading (line-of- sight/VHF) channels K=3 suffices (A). Options C/D wrongly assign baud values to K, which is not a baud rate.
U0741. The necessary bandwidth Bn of FM voice depends on the peak frequency deviation
调频话的必要带宽Bn取决于FM信号的峰值频偏D与最高调制频 率M。估算方法为：
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This is Carson's rule: Bn ≈ 2(D + M), i.e. twice the sum of peak deviation D and the highest modulating frequency M (A). The other formulas mis-weight D and M (e.g., Bn=2M+D or M+2D) and thus are incorrect.
U0742. The modulation methods used for slow-scan television (SSTV) and radio facsimile (FAX) in the amateur bands are both:
业余频段中的慢扫描电视（SSTV）和无线电传真（FAX）的调 制方式都是：
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Amateur SSTV and radio facsimile (FAX) are normally transmitted using FM (frequency modulation) of the voice channel — the picture's audio baseband modulates the carrier (A). They are not AM, PM, or CW for the image transmission.
U0743. What amateur radio slow-scan television transmits is:
业余无线电慢扫描电视所传送的是：
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SSTV (slow-scan television) sends a still (static) picture, one scan line at a time, over several seconds (A). It is not moving video and typically not interlaced like fast-scan TV.
U0744. A certain amateur station intends to transmit several circuit diagrams with a resolution of 1024×768 pixels or somewhat higher over a short-wave voice channel. Appropriate modes of communication could be: (Choose all that apply.)
某业余电台拟通过短波话音信道传输几张分辨率为1024x768 像素或更高一些的电路图。适当的通信联络方式可以是：
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Over a short-wave voice (SSB) channel you can send moderate- resolution still images with digital SSTV (DSSTV, supports higher resolution) or radio facsimile (FAX) (A, B). Plain analog SSTV (D) is lower resolution and typically used on FM; ATV (C) needs several MHz of bandwidth and is not feasible on a narrow HF voice channel.
U0745. When receiving SSTV signals in modes such as Robot, Scottie, Martin, SC2, or PD, we hear a periodic, very brief "click, click" sound; they are:
接收Robot、Scottie、Martin、SC2或PD等方式的SSTV信 号时，我们会听到一种周期性的，非常短促的“咯、咯”声， 它们是：
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At the start of each scan line, SSTV sends a short visicorder/line sync tone — the periodic "click" you hear is the line synchronization signal (A). It is not a parasitic oscillation, a standard-frequency tone, or a beat note.
U0746. SSTV communication provides different transmission modes such as Robot, Scottie, AVT, and Martin. The specific differences are:
SSTV通信提供了Robot、Scottie、AVT、Martin等不同传输 方式。具体区别是：
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The SSTV modes differ mainly in their technical parameters — pixel resolution, how pixels are modulated, line frequency, and frame frequency — letting operators trade off picture quality and robustness to conditions (A). They mostly occupy similar audio bandwidth, and the differences are not fundamentally about receiver sensitivity or "difficulty".