CRAC Class C (2025) — Questions 11–20

发射 (emission) is radiation or radiation products produced by a radio transmitting station. Spurious products sent by an amateur station are emissions (A). B's receiver local-oscillator leakage is not from a "transmitting station"; C and D are non-station sources (medical/therapeutic and lightning), not emissions from a radio transmitter.

These four are exact ITU definitions: 无线电测定 = radiodetermination (determining position/velocity/characteristics via radio-wave propagation); 无线电导航 = radionavigation (radiodetermination for navigation including obstacle warning); 无 线电定位 = radiolocation (radiodetermination other than navigation); 无线电测向 = radio direction finding (determining direction by receiving waves). All four are correct.

An 业余无线电台 is defined as one or more transmitters, receivers, or a transmitter–receiver combination (with accessories) used for the amateur service — so a station may contain multiple units (A). B/C/D wrongly restrict a station to a single transmitter or receiver.

业余业务 (amateur service) is for self-training, intercommunication, and technical study by operators; 卫星业余业务 (amateur-satellite service) uses space stations on satellites for the same purposes. A and B are correct definitions. C and D are wrong because operators/stations may communicate only within the amateur and amateur-satellite services, not other services.

An 业余无线电爱好者 (amateur radio operator) is a person formally authorized and interested in radio technique, with interest purely personal and not for profit (A, B). C (may seek profit) and D (only adults) contradict the definition; minors may be licensed.

发射类别 (emission class) is a set of emission characteristics denoted by standard symbols, including main-carrier modulation, modulating signal, type of information sent, and other applicable signal characteristics (A, B). C and D are irrelevant statements about station composition, not emission class.

单边带发射 (SSB) is amplitude modulation in which only one sideband is transmitted (A). It is AM-based, not FM (so B, D are wrong), and although the carrier is suppressed, the defining feature in the standard definition is transmission of one sideband, making A the exact definition.

干扰 (interference) is the effect of unwanted energy from emissions/radiation/induction on reception — showing as performance degradation, misinterpretation, or information loss, and such effects would not occur without that unwanted energy (A, B, C). D contradicts the definition.

有害干扰 (harmful interference) is interference that endangers radionavigation/safety services or seriously degrades, obstructs, or repeatedly interrupts lawful radiocommunication (A, B). C (no penalty) and D (only avoid interfering with other hams) are false; harmful interference is penalized and protection extends beyond amateur services.

Secondary-service stations (次要业务台站) must not cause harmful interference to, and may not claim protection from, primary-service stations already assigned or potentially assigned frequencies (A, B). They may seek protection from future same/other secondary stations (C). D is a false generalization about amateur use.