U0421. What is the function of the speech compression feature in an
SSB transmitter?
单边带发信机的语音压缩功能有什么作用？
Explanation · 解析
Speech compression (语音压缩 / speech processing) reduces the
peaks and lifts the troughs of the voice waveform so the
average level — and thus the perceived loudness/SNR at the far end — is higher without exceeding the ALC limit. Option A is
correct. B is the opposite (it reduces dynamic range, not increases it usefully); C is equalization, not compression; D is
untrue — compression does not shrink occupied bandwidth
and can even widen it if overdone.
U0422. What function does the symbol PROC on the transceiver
panel represent?
收发信机面板上的符号PROC代表什么功能？
Explanation · 解析
PROC = speech processor/compression (语音压缩) on transmit.
It boosts low-level speech so the average modulation is higher.
Option A is correct. B is PRE, C is AT/TUNE, D is ALC.
U0423. When transmitting, what problem may improper adjustment
of speech compression cause?
发信时，若话音压缩调整不当可能带来什么问题?
Explanation · 解析
Over-driving the speech processor generates heavy harmonics and intermodulation products (互调成分) that spread outside
the channel, degrading the other station's ability to copy you
and causing adjacent-channel interference. Option A is correct. B is wrong (distortion does hurt copy); C (hum) is a
ground/PSR issue, not compression; D — a processor will not damage the mic.
U0424. Why should the speech compression function be turned off
when sending AFSK signals with an SSB transceiver?
为什么用单边带收发信机发送AFSK信号时应关闭语音压缩功
能？
Explanation · 解析
AFSK data tones need a clean, stable envelope; speech compression reshapes/limits that envelope, distorting the
mark/space transitions (baseband) and raising the bit error rate (误码率). Hence compression must be off for data. Option A is
correct. B and C are false (compression doesn't remove phase
or all amplitude); D is backwards — compression lowers peak- to-average, not raises it dangerously.
U0425. When an amateur station measures transmit power and
antenna SWR by transmitting, what must be noted and done
is:
业余电台以发射的方法测量发射功率和天线驻波比时必须留意
并做到的是：
Explanation · 解析
Measuring by actually transmitting radiates a signal, so to
avoid causing harmful interference (有害干扰) you must do it on a clear, unused frequency away from busy calling/simplex
frequencies. Option A is correct. B (point north) is irrelevant; C (turn on compression) is wrong for a clean carrier
measurement; D's specifics are not the required rule.
U0426. An SSB amateur station needs to transmit a steady
continuous signal to test and check the antenna SWR. The
courteous way to do it is:
单边带业余电台测试检查天线驻波比需要发射平稳的连续信
号。文明的作法是：
Explanation · 解析
To measure SWR you need an unmodulated (or steady) carrier, not voice. The courteous method is CW key-down, or AM/FM
with PTT held but silent (no speech), giving a clean continuous
carrier, then return to SSB. Option A is correct. Whistling or voicing (B/C/D) sends modulated, intelligible — and thus
potentially interfering — audio onto the air, which is neither clean nor courteous.
U0427. What function do the symbols AT or TUNE on the transceiver
panel represent?
收发信机面板上的符号AT或者TUNE代表什么功能？
Explanation · 解析
AT / TUNE = automatic antenna tuner (自动天线调谐): it matches the transmitter to the antenna by sensing the SWR
and adjusting a matching network for the lowest SWR. Option A is correct. B is transmit AVC; C is ALC; D is AFC.
U0428. When listening with a communications receiver that has
separate RF/IF gain and audio gain controls, you can set it like
this:
使用射频/中频增益和音频增益分开控制的通信接收机进行收听
时，可以这样设置：
Explanation · 解析
With separate RF/IF gain and audio gain, the best practice is: for a very weak signal maximize RF/IF gain (to keep the best
SNR before the noise floor) and use audio gain only for
comfort; for a very strong signal you can max audio gain but must reduce RF/IF gain (or use ATT) to avoid front-end
overload, then set the other control for volume. Option A captures this. B reverses the weak-signal rule (max audio on
weak signal just raises hiss); C/D's fixed-middle rules ignore the
weak/strong distinction.
U0429. Compared with VHF or UHF communication, what is the
biggest difference of HF communication?
HF通信与VHF或UHF通信相比，最大的不同是什么？
Explanation · 解析
The defining feature of HF (short wave, 3–30 MHz) is skywave
propagation — signals refract off the ionosphere (电离层) and return to Earth, enabling intercontinental communication.
VHF/UHF are essentially line-of-sight. Option A is correct. B is false (HF fading is often severe); C is false (HF antennas are
larger, e.g. 40 m dipole ≈ 20 m); D is false (HF channels are
narrow, not broadband).
U0430. Which of the following methods can reduce the RF current
that may be induced in the audio cable of a microphone or
headphones?
下面哪种方法可以减小话筒或耳机用音频电缆可能感生的射频
电流？
Explanation · 解析
RF current induced on an audio lead is best suppressed by a
ferrite choke (铁氧体磁环) slipped over the cable — it adds
common-mode impedance at RF without affecting the audio. Option A is correct. Putting filters in the core wire (B/D) would
distort the audio; a mic amp (C) does nothing for RFI. 收发信机面板控制 Transceiver Front-Panel Controls