Continuing from the previous section, this tutorial focuses on building a UHF Yagi antenna array for lunar and terrestrial communication.
1. Intermediate website goals: To be able to see and communicate with more medium-sized ground stations, and to perform echo tests using reflected signals from the Moon's surface, ensuring that the measured solar noise is at least 5 dB.
2. The parameters for the antenna array being constructed are an 8x10e Yagi, with a spacing of 1m. Simulation results show a gain of 22.69 dBi and a front-to-back ratio of 28.9 dB. Four antennas in a group are connected together using a 1:4 power divider, and the other two groups are connected together using a 1:2 power divider. After passing through the BU435 amplifier, the signal is fed to the radio via a 7/8 feed cable.
3. Proposed Solution: Four 10-element low-noise Yagi antennas (made by BG7XWF), with a 4m truss support, costing 400 yuan.400), Yaesu G5500 rotator, Yaesu rotator computer communication box (made by BG4WOM), BU435 preamplifier, 1.4:1 power divider2, 1.2-split power divider1, Precast concrete blocks (500500500), rotating machine control cable 0.75 mm60m2 pieces, 7/8 inch connectors50m, 12 with 3m length LM400 cable, 40mm aluminum pipe, hand and foot stand cross clamp.
4. Assembly:
4.1 Preliminary Preparation: Rotor, control lines, rotor control box, connection and testing confirmed, with proper labeling and cable identification.
Dig a hole (600600(1000), and then place the prefabricated concrete blocks inside.
4.2 Assemble the Yagi antenna, and after installation, perform a range test to measure the antenna's VSWR (Voltage Standing Wave Ratio) to ensure consistent Yagi parameters. Measure the Yagi feed (center conductor and coaxial cable outer diameter) to ensure consistent phase.
4.3 Prepare the cut aluminum pipes, level the ground, assemble the pipes, and ensure they are aligned.
4.3 Installing the Yagi antenna: Pay attention to the center of gravity. The Yagi ensures all elements are in phase. After installation, connect the splitter and jumper cables.
(The phase was reversed in the image; it has been re-adjusted and installed.)
4. Assemble the frame and Yagi antenna array, marking and preparing the holes for installing expansion screws. Carefully erect and level the Yagi antennas, backfilling with sand, bricks, and soil, and compact with water. (Before installation, ensure the rotator is pointing towards 0 degrees north, aligned with the ground plane.)
4.5 Link feed cable, control cable.
- Calibrate the rotator and set the direction in the psrotator control software.
The direction of the rotating shaft and the direction of the control head are consistent, but the voltage output to the control box may not always be a standard value. For example, if the output is 0 degrees, it may be accurate; however, for 180 degrees and 360 degrees, there may be some deviation.
The calibration method provided by BG4WOM teacher: 1. Ensure that 0 degrees is correct, manually rotate the rotator to 360 in the control head, and the actual antenna should also be 360 degrees. At this point, the computer display value will be inaccurate. Adjust the red-ringed adjustable screw behind the rotator (5500), left side horizontal, right side tilt, and use a potentiometer to make the computer display value consistent with the actual value.
6. Calibrate the rotator direction. Calibration requires aligning with magnetic north, and there are multiple calibration methods.
6.1 Solar Noise Calibration
This method involves using a fixed solar orbit, tracking the sun with a PS rotator, and observing solar noise using the Spectravue software. By repeatedly correcting deviations, we can determine the maximum level of solar noise. (Due to interference from the 432 city direction, it is necessary to find the appropriate azimuth and frequency (otherwise, the solar noise and background interference will add up, resulting in a low confidence level for the noise value), and the G5500 controller has a small angular response delay, so manual correction is recommended on the control head).
(For solar noise testing, you need to disable the radio's AGC (Automatic Gain Control), set the RF gain to maximum, and enable the pre-amplifier in SSB mode.)
6.2 Compass Calibration
A compass can measure the actual magnetic north direction, but it also has some degree of error.
6.3 Triangulation Calibration
By using satellite maps to determine the antenna's location and the position of a fixed camera, and by performing triangulation based on distance measurements, it was calculated that the Yagi antenna should be aligned with 207 degrees. This means that aiming the long-range lens of the camera at the Yagi antenna array will achieve the desired targeting.
(This method works best in practice.)
7. The actual EME reception test results were very good. We conducted tests over two weekends, on November 10 and 11, and we could clearly see the signal when the moon rose by one degree.
Remember to perform spectrum normalization for the air channel, and use Q65 synchronization for the spectrum plot.
P.S.: The IC9700 initially failed to receive any signal, and the spectrum appeared to be abnormal. After a long investigation, it was determined that the problem was due to an internal setting issue within the IC9700 itself.
Previously, in order to link the icom RSBA software, the "output select" option for the ACC was changed to IF output, which caused a problem.
闽ICP备2021006864号-7
闽公网安备35020602002794号