CRAC Class C (2025) — Questions 211–220
Unofficial study reference only. Not affiliated with the FCC, NCVEC or CRAC — official sources prevail. 非官方学习参考，与 FCC、NCVEC、CRAC 无隶属关系；以官方发布为准。
U0255. The correct way to fill in and mail a QSL card is:
填写和邮寄QSL卡片的正确做法是：
Exam tips · 考试提示
For a prompt direct return, mail your card to the other station's address with a SASE (self-addressed stamped envelope) enclosed. Option A is correct. B (correction fluid/overwriting) makes a card look altered; C confuses QTH (operating location) with mailing address (should go in the address area, not QTH); D is contradictory — "via bureau" vs "QSL DIRECT".
U0256. When exchanging QSL cards, we sometimes meet a special kind of radio enthusiast who only sends us a listening (SWL) card. After confirming the card's contents we promptly return a card out of respect. This kind of enthusiast is:
交换QSL卡片时，我们时有遇见一类特殊的无线电爱好者，他 们仅向我们寄发收听卡片。而我们在确认卡片所载内容之后会 立即回卡以示敬意。这类爱好者是：
Exam tips · 考试提示
A shortwave listener (短波收听者, SWL) is not a licensed transmitting operator but sends "listener" QSLs confirming they heard your station. Option A is correct. Broadcast enthusiasts listen to broadcasts (not typically sending amateur QSLs), and DIY/monitor labels do not fit.
U0257. When working through a repeater, we should preset the radio's receive/transmit offset in advance, so we can smoothly handle operations on the uplink or downlink frequencies and avoid setting things up mid-contact and making mistakes. The uplink/downlink frequency offsets of amateur repeaters in the 144 MHz and 430 MHz bands are, respectively:
通过中继台进行通联时，我们应事先设好电台的接收和发射频 差，以便顺利应对上行或下行频率上的各种操作，避免边联络 边设置，忙中出错。144和430MHz频段业余中继台的上下行 频差分别为：
Exam tips · 考试提示
In China, 2 m (144 MHz) repeaters use a 0.6 MHz offset (typically −0.6 MHz) and 70 cm (430 MHz) repeaters use a 5 MHz offset (typically +5 MHz). Option A gives the correct pair. B lists channel step sizes, not offsets; C/D are wrong offsets.
U0258. If you call a specific amateur station through a repeater, you should:
如果通过中继台呼叫一部业余电台，你应当：
Exam tips · 考试提示
A directed call through a repeater uses the same format as any directed call: name the station you're calling, then your own call. Option A is correct. B (break, break) and C (a CQ) are not directed calls; D is passive and unnecessary.
U0259. The principle for using an amateur repeater is:
业余中继台的使用原则是：
Exam tips · 考试提示
Repeaters must stay available for emergencies, so their uplink/downlink should be idle except for brief necessary contacts (A). B (keep busy) defeats that purpose; C/D (association notices, student study chat) are not the stated priority principle and can congest the machine.
U0680. Deep space means space at a distance from the Earth approximately equal to or greater than which of the following values?
深空（deep space）是指离地球的距离约等于或大于下列值的 空间：
Exam tips · 考试提示
By the ITU/space convention, deep space begins at a distance of about 2 × 10⁶ km (2 million km) from Earth — roughly beyond the Moon's orbit (A). The smaller values in B/C/D are within cis-lunar or near-Earth space.
U0681. The orbital inclination of an amateur Earth satellite is defined as including:
业余地球卫星的轨道倾角（inclination）是指包含：
Exam tips · 考试提示
Orbital inclination is the angle between the orbital plane and the equator, defined at the ascending node (where the satellite crosses the equator going north) and measured in the counterclockwise (prograde) direction (A). The descending- node or clockwise variants are not the standard definition.
U0682. The period of an amateur satellite means:
业余卫星的周期（period）是指：
Exam tips · 考试提示
An orbital period is the time for the satellite to return to the same point on its orbit — equivalently, one full revolution around Earth (A). The intervals over a ground point (B), the equator (C), or the pole (D) depend on the orbit and are not the definition of the period.
U0683. A geosynchronous satellite means:
地球同步（geosynchronous）卫星是指：
Exam tips · 考试提示
A geosynchronous satellite has an orbital period equal to Earth's sidereal rotation period (~24 h) (A). B describes a sun- synchronous orbit, C a polar orbit, and D a sun-synchronous orbit — not geosynchronous.
U0684. A Sun-synchronous orbit satellite means:
太阳同步（轨道）（Sun-synchronous orbit）卫星是指：
Exam tips · 考试提示
A Sun-synchronous orbit precesses so the orbital plane maintains a fixed angle to the Sun (A). B and C describe a geostationary satellite, and D a geosynchronous satellite — not sun-synchronous.