CRAC Class C (2025) — Questions 451–460
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.
U0802. BD0ZZ hears an SSB 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SSB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
The correct SSB reply states the partial call you heard, your own call, and politely asks for the missing prefix — concise and clear. "QRZed?" (B) means "who is calling me?", and the verbose options (C/D) are poor operating practice.
U0803. The meaning of the DX Summit message "PY2SS 28005.3 KH6/N6GQ simplex, fading signal in SA 2040 15 Feb 2012" is:
DX Summit消息“PY2SS 28005.3 KH6/N6GQ simplex, fading signal in SA 2040 15 Feb 2012”的意思是：
Exam tips · 考试提示
PY2SS is a Brazilian (PY) station; KH6 is Hawaii; "fading signal in SA" (South America) means the Brazilian reporter heard the Hawaiian station with a weak, fading signal — i.e., poorly. Guam would be KH2/KH0, not KH6.
U0804. The meaning of the DX Summit message "JA2WS 14009.6 E51WWA Calling CQ, no takers, Cook Is 0052 14 Feb 2018" is:
DX Summit消息“JA2WS 14009.6 E51WWA Calling CQ, no takers, Cook Is 0052 14 Feb 2018”的意思是：
Exam tips · 考试提示
The spot format is: reporter (JA2WS) heard station (E51WWA) doing something. "E51WWA Calling CQ, no takers, Cook Is" means the Cook Islands station E51WWA was calling CQ with no replies. JA2WS is the reporter, not the caller.
U0805. SSTV contacts on the 20 m band are most commonly found at:
20米波段的SSTV联络最常见于：
Exam tips · 考试提示
On 20 m, SSTV activity is conventionally centered around 14.230 MHz (USB). 14.260 is the IOTA/SSB area, 14.040/14.030 are CW segments, so those are not the SSTV spot.
U0806. IOTA activity on the 20 m band is most commonly found at:
20米波段的IOTA活动最常见于：
Exam tips · 考试提示
IOTA (Islands On The Air) hunters conventionally gather at 14.260 MHz for SSB and 14.040 MHz for CW on 20 m. The other SSB/CW pairings are not the standard IOTA centers.
U0807. According to contest convention, the frequencies generally NOT used for the IOTA contest are:
按照竞赛惯例，通常不用于IOTA竞赛的频率有：
Exam tips · 考试提示
IOTA contest band plans avoid the top of the 80 m CW segment 3560–3600 kHz (it is reserved/avoided by convention), while the other ranges listed are within normal IOTA operating segments. Per the question's key, 3560–3600 kHz is the non- IOTA frequency block.