CRAC Class B (2025) — Questions 181–190
U0186. The band allocated by our country to the amateur service and amateur-satellite service that falls within the low-frequency (LF) range is:
我国分配给业余业务和卫星业余业务的属于低频（LF）范围的 频段为：
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The LF (低频/长波) amateur band is 135.7–137.8 kHz (A). 472–479 kHz is actually MF (中频), and B/C are not amateur allocations.
U0187. Short-wave amateur stations should avoid transmitting within ±500 Hz of the IARU beacon operating frequencies. Those frequencies are:
短波业余电台应避免在IARU信标工作频率±500Hz的范围内发 射电波。这些频率是：
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The IARU international beacons (NCDXF/IARU) operate on 14.100, 18.110, 21.150, 24.930, and 28.200 MHz; amateurs must keep clear of these within ±500 Hz (A). The other options mix in wrong frequencies.
U0188. On the 7 MHz band, the frequency range a Chinese short-wave amateur station may actually occupy when conducting LSB voice contacts is:
我国短波业余电台在7MHz频段进行LSB通话时可以实际占用的 频率为：
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For LSB (lower sideband) on 7 MHz, the carrier is placed above the band's 7.000 MHz lower edge by roughly one sideband width (~3 kHz), so the usable carrier range is 7.030–7.200 MHz (A). Options that start at 7.000 MHz would push the lower sideband below the band edge (B, D) or use an incorrect offset (C).
U0189. On the 14 MHz band, the frequency range a short-wave amateur station may actually occupy when conducting USB voice contacts is:
短波业余电台在14MHz频段进行USB通话时可以实际占用的频 率为：
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For USB on 14 MHz, the carrier is raised above 14.000 MHz by about one sideband width so the lower sideband stays in-band, giving 14.100–14.350 MHz (A). The upper edge is the band limit 14.350 MHz. B starts too low (14.030 would push the lower sideband below 14.000); C/D truncate the upper edge.
U0190. On the 18 MHz band, the frequency range a short-wave amateur station may actually occupy when conducting USB voice contacts is:
短波业余电台在18MHz频段进行USB通话时可以实际占用的频 率为：
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The 18 MHz WARC band is 18.068–18.168 MHz. For USB voice, the carrier is offset above 18.068 by one sideband width and capped at the 18.168 upper edge, giving 18.1105–18.168 MHz (A). B/C/D overreach the band edges.
U0191. On the 21 MHz band, the frequency range a short-wave amateur station may actually occupy when conducting USB voice contacts is:
短波业余电台在21MHz频段进行USB通话时可以实际占用的频 率为：
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On 21 MHz (15 m), USB voice occupies 21.125–21.45 MHz, but must exclude the IARU beacon at 21.150 MHz (±500 Hz → 21.1495– 21.1505) (A). B omits the beacon exclusion; C/D use the wrong lower edge (21.000).
U0192. On the 24 MHz band, the frequency range a short-wave amateur station may actually occupy when conducting USB voice contacts is:
短波业余电台在24MHz频段进行USB通话时可以实际占用的频 率为：
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The 24 MHz WARC band is 24.89–24.99 MHz. USB voice starts above the 24.930 beacon (the 24.930 MHz IARU beacon plus offset) and ends at the 24.99 upper edge, giving 24.9305–24.99 MHz (A). Other options ignore the beacon exclusion or use wrong edges.
U0193. On the ~29 MHz band, the frequency range a short-wave amateur station may actually occupy when conducting USB voice contacts is:
短波业余电台在29MHz频段进行USB通话时可以实际占用的频 率为：
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The 10 m band is 28–29.7 MHz. For USB voice near the top, the usable window is 28.3–29.3 MHz (A) — kept below 29.7 to contain the upper sideband and above 28.3 to keep the lower sideband in- band. B/D use the full band edges (sideband would spill), and C reaches the 29.7 top edge.
U0194. On the ~29 MHz band, the frequency range a short-wave amateur station may actually occupy when conducting FM voice contacts is:
短波业余电台在29MHz频段进行FM通话时可以实际占用的频 率为：
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FM needs a wider bandwidth, so on 10 m it is confined to the top of the band, 29.51–29.7 MHz (A), which is the FM/repeater segment. B is too wide; C and D include the SSB/lower regions. (Note: option C in the source contains a stray character "z", preserved verbatim.)
U0195. When conducting local contacts on the 144 MHz band, the frequencies a VHF amateur station should avoid occupying are:
VHF业余无线电台在144MHz频段进行本地联络时应避免占用 的频率为：
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For local 2 m work you should avoid 144–144.035 MHz (EME / weak-signal / propagation) and 145.8–146 MHz (satellite uplink/downlink) (A). B is the main simplex/voice region you should use; C/D list sub-segments, not the protected edges.