CRAC Class C (2025) — Questions 601–610

U0483. Assume both receiving and transmitting antennas use half- wave dipoles. For short-distance communication between ground stations, the best polarization arrangement for the receiving and transmitting antennas should be:

假设接收和发射天线均使用半波长偶极天线，则在地面台站间 的近距离通联中，接收和发射天线的最佳极化方式应当安排 为：

U0484. A right-hand polarized wave means, on any plane perpendicular to the direction of propagation, when viewed along the direction of propagation the electric-field vector rotates clockwise (to the right) with time — an elliptically or circularly polarized wave. If a ground amateur station observing an amateur satellite finds that the electric field of the radio wave arriving from the satellite rotates clockwise, then the polarization of that signal is:

右旋极化波是指在垂直于传播方向的任意平面上，沿传播方向 观察时，电场矢量为随时间向右（顺时针）旋转的椭圆或圆极 化波。如果地面上某业余电台在观测业余卫星时发现从卫星到 达该台的无线电波的电场是顺时针旋转的，则该信号的极化方 式为：

U0485. In line-of-sight communication, given the transmitting antenna is a left-hand circularly polarized antenna pointing at the receiving point, the best polarization for the receiving antenna is:

在视距通联中，已知发射天线为指向接收点的左旋圆极化天 线，接收天线的最佳极化方式为：

U0486. A satellite's downlink uses a right-hand circularly polarized antenna, flies from north to south, and the antenna always points at the Earth's south pole. If a ground amateur station uses a circularly polarized antenna to auto-track the satellite, the best polarization for that station's antenna should be:

某卫星下行链路采用右旋圆极化天线，从北向南飞行，天线始 终指向地球的南极。如果地面上某业余电台采用圆极化天线自 动跟踪该卫星，则该台所用天线的最佳极化方式应当为：

U0487. It is known that a satellite's downlink transmitting antenna is a dipole pointing at the ground. Because the satellite keeps rotating, the polarization direction of the wave received by the ground station keeps changing. To avoid polarization issues interrupting reception, the receiving antenna can be:

已知某卫星下行信号的发射天线是指向地面的偶极天线。由于 卫星不断旋转，地面台站所收电波的极化方向就会不断变化。 为了不至极化问题致使接收中断，接收天线可以是：

U0488. An amateur station using a half-wave vertical dipole for a contact receives an S4 signal strength at the other end. Now, with transmit power unchanged, the transmitting station switches to a Yagi antenna with 8.15 dBi gain (maximum radiation direction and polarization unchanged). What does the received signal strength at the other end become? [Hint: the receiver's S-meter increases by 6 dB per step from S1 to S9]

某业余电台使用半波垂直偶极天线通联时，对方所收信号的强 度为S4。现发射功率不变，发信方改用增益为8.15dBi的八木 天线（最大辐射方向和极化均不变），则对方所收信号的强度 变为：【提示：收信机信号强度指示从S1至S9每档增加6dB】

U0489. An amateur station transmitting with a half-wave vertical dipole yields an S4 received signal at the other end. Now, power unchanged, the transmitting station switches to a Yagi with 12 dBd gain (direction and polarization unchanged). What does the received strength become? [Hint: S-meter +6 dB per step]

某业余电台使用半波长垂直偶极天线发射时，对方所收信号的 强度为S4。现发射功率不变，发信方改用增益为12dBd的八木 天线（最大辐射方向和极化均不变），则对方所收信号的强度 变为：【提示：收信机信号强度指示从S1至S9每档增加6dB】

U0490. Two amateurs use half-wave vertical dipoles to contact each other; each receives the other's signal at S4. Now, with transmit power unchanged, both switch to Yagis with 8.15 dBi gain (direction and polarization unchanged) and make contact again. What do both signals' strengths become? [Hint: S-meter +6 dB per step]

两位业余爱好者使用半波长垂直偶极天线相互通联，双方所收 信号的强度均为S4。现双方发射功率不变，都改用增益为 8.15dBi的八木天线（最大辐射方向和极化均不变）再次联络， 则双方信号的强度变为：【提示：收信机信号强度指示S1至S9 每档增加6dB】

U0491. Even on an open plain or vast desert, the strength of locally received VHF/UHF signals changes periodically as the equipment moves. The main reason is:

即便是在辽阔的平原或广袤的戈壁，我们所收本地VHF/UHF信 号的强度也会伴随设备的移动而发生周期性的变化。主要原因 是：

U0492. A phenomenon in VHF/UHF contacts: if a distant station gives a poor signal report, merely moving a few steps or changing the operating frequency by tens of kHz can significantly improve communication. This is because:

在VHF/UHF频段通联时的一个现象，如果远方电台给出的信号 报告很差，则仅需移动几步或将工作频率改变数十千赫就可能 显著改善通信效果。这是因为：