CRAC Class B (2025) — Questions 491–500
U0792. 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:
一部业余无线电台以CW方式发射时的载波输出功率为10瓦， 电源效率约为80%。若该台连续发报10秒钟，则此期间的平均 发射功率：
Exam tips · 考试提示
CW text consists of dots and dashes with spaces (off periods), so the carrier is not on 100% of the time; the time-averaged power is well below the 10 W key-down carrier level. The 80% efficiency is a distractor for the RF average.
U0793. 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:
一部业余无线电台以SSB方式发射时的峰值输出功率为10瓦， 电源效率约为80%。若该台连续发话10秒钟，则此期间的平均 发射功率：
Exam tips · 考试提示
The 10 W given is peak envelope power (PEP) — the momentary voice peak. Normal speech averages only about 20–30% of PEP, so the average RF power over 10 s is far below 10 W. The 80% efficiency concerns DC input, not the RF average.
U0794. 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:
一部业余无线电台以SSB方式发射时的峰值输出功率为10瓦， 电源效率约为80%。若该台利用此方式发送一条时长12.6秒的 FT8消息，则此期间的平均发射功率：
Exam tips · 考试提示
Although the SSB rig's PEP is 10 W, FT8 is a constant-amplitude (constant-envelope) 8FSK signal, so it drives the transmitter at full PEP continuously for the whole 12.6 s. Thus the average RF power ≈ 10 W (PEP = average here).
U0795. 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:
一部业余无线电台以SSB方式发射时的峰值输出功率为10瓦， 电源效率约为80%。若该台利用此方式发送一条时长12.8秒的 PSK31消息，则此期间的平均发射功率：
Exam tips · 考试提示
PSK31 (BPSK/QPSK) is phase modulation with constant envelope, so like FT8 it holds the transmitter at full PEP continuously; average RF power over the 12.8 s ≈ 10 W. The efficiency figure is irrelevant to the RF average.
U0796. 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:
一部业余无线电台以SSB方式发射时的峰值输出功率为10瓦， 电源效率约为80%。若该台利用此方式发送一段时长10秒的 Robot 8 SSTV黑白图像，则此期间的平均发射功率：
Exam tips · 考试提示
Analog SSTV over SSB is a near-constant-amplitude FM-like signal (the picture modulates the audio tone continuously), so the transmitter runs at essentially full PEP throughout the 10 s scan; average RF power ≈ 10 W. DX 与竞赛操作 DX and Contest Operating
U0797. How do you call all DX stations?
如何呼叫所有DX电台？
Exam tips · 考试提示
"CQ DX" is the standard general call specifically inviting any distant (DX) station to answer. "CQ AF/SA/OC" would restrict the call to a continent (Africa/South America/Oceania), not "all DX".
U0798. Which of the following describes good habits for participating in DX contacts and amateur radio contests?
以下哪项描述了参加DX联络以及业余无线电竞赛的良好习惯？
Exam tips · 考试提示
Good DX/contest practice is to be brief — only your call sign and the required exchange — to keep the frequency efficient. Repeated contacts (B) are redundant, partial call signs in a pile- up (C) cause confusion, and raising power against noise (D) does not help reception and causes interference.
U0799. Participating in DX net communication helps establish contacts with some rare stations. The correct practice is:
参加DX网络通信有助于与一些稀有电台建立通信。正确做法 是：
Exam tips · 考试提示
A DX net is run by a Net Control Station (主控台) that schedules who works the rare station; you must follow the net's procedure and only answer when invited. Calling on your own (B), breaking in (C), or simply CQing (D) disrupts the net and is improper.
U0800. If there is an unavoidable strong noise source near a short- wave amateur station that affects reception of weak signals, the reasonable approach is:
如果短波业余电台附近环境有不可避免的强烈噪声源影响接收 微弱信号，合理的做法是：
Exam tips · 考试提示
When local noise blocks your receiver, transmitting louder (B/D) does not help you hear others and only creates interference; the sensible approach is to restrict yourself to stations you can copy and, if calling, use lower power to minimize nuisance. Turning down RF gain (C) would only worsen weak-signal copy.
U0801. BD0ZZ hears a CW call from an amateur station and wishes to contact it. However, he only caught the district number and the suffix 2MAX of the other station's call sign. The correct reply at this moment should be:
BD0ZZ听到某业余电台的CW呼叫并希望与之联络。但是，他 只听清对方呼号的分区号和后缀为2MAX。此时的正确回叫应 当是：
Exam tips · 考试提示
In CW, when you only partially copy a call you send "?" before the part you heard (?2MAX), your own call (DE BD0ZZ), and K to invite a reply — the standard way to ask the other station to repeat its full call. The other options add unnecessary or incorrect text.