CRAC Class A (2025) — Questions 641–650

频率容限 (frequency tolerance) is the maximum permitted deviation of the emission's frequency from the assigned/reference frequency. Both standard expressions are accepted: the center frequency of the occupied band deviating from the assigned frequency (A), and the characteristic frequency deviating from the reference frequency (B). C and D compare against the wrong reference (highest/necessary frequency).

Frequency tolerance is given either as a relative figure, parts per million (百万分之几, A), or as an absolute value in hertz (赫 兹, B). Percent (C) and megahertz (D) are not the standard units for stating tolerance.

Spurious-domain emission power (杂散域发射功率) is specified as an absolute level in dBm (A), relative to the carrier in dBc (B), or relative to PEP in dB (C). A plain absolute wattage (D) without a reference is not how the limit is normally stated.

杂散发射 (spurious emission) is emission outside the necessary bandwidth that can be reduced without harming the wanted transmission (A), and it includes harmonics, parasitics (B), and intermodulation/frequency-conversion products (C). Per ITU it is distinct from out-of-band emission (带外发射), so D is incorrect.

Dedicated amateur equipment must keep frequency tolerance and spurious radiation within limits and must transmit only on the state-prescribed amateur and amateur-satellite frequencies (A). B wrongly says tolerance need only be "not lower than" the limit, C's "including" wording is vague/incorrect, and D inverts the power rule (power must not exceed the limit).

Damped-wave (减幅波) radiation is produced by discontinuous spark discharges — e.g., arcing at a loose/poor circuit contact (A). A keyed transmitter (B), TV LO leakage (C), and medical heater leakage (D) produce continuous or other emissions, not the classic damped spark wave.

GB 8702-2014 exempts, from management, radio- communication facilities below certain equivalent radiated power (ERP): 0.1–3 MHz with ERP < 300 W (A) and 3 MHz–300 GHz with ERP < 100 W (B). The blanket exemptions for all amateur stations below/above 30 MHz (C, D) do not exist — amateur stations are still subject to the limits.

公众曝露 (public exposure) under GB 8702-2014 is the total electric-, magnetic-, and electromagnetic-field exposure received by the general public (A). Occupational exposure (B) and medical exposure (C/D) are distinct categories with their own limits.

The limits vary with frequency because the human body's absorption of electromagnetic energy depends on frequency (resonance and absorption peaks at certain wavelengths), so exposure limits are shaped accordingly (A). B is false (low frequencies do penetrate/induce), C is irrelevant, and D reverses the physics (higher frequency = higher photon energy).

Homebrew/modified/assembled transmitters must meet the relevant national standards — both the amateur-equipment RF standard GB/T 32658-2016 (A) and, for shortwave SSB gear, GB/T 16946-2017 (B); the authority may test such equipment free of charge (C). D is false: homebrew equipment is still subject to radio-management supervision.