From：Zhaoqing Xiangjiasheng Technology Co., Ltd Release time：2020-05-08
Radio waves are a kind of energy. According to the law of conservation of energy, high-gain antennas do not increase the total energy of radio waves, but concentrate the radio waves into a narrow space, and the radio wave density in that space is strengthened. Low-gain antennas scatter radio waves into a wider space.
The most suitable analogy is the flashlight. The antenna is quite similar to the flashlight reflector. Adjusting the flashlight reflector may focus the light on a smaller spot. You will find the spot illuminated is very bright, but the periphery is dark, suitable for watching For distant objects, the field of view is narrow; the flashlight is adjusted to the astigmatism state, and the surrounding light intensity is relatively average. It is suitable for seeing objects at close range and has a wide field of view.
The energy of light waves is conserved. Under the same conditions, the reflector of the flashlight does not change the brightness of the bulb itself.
The same is true for radio waves. The antenna does not change the power of the transmitter, nor does it amplify the power of the transmitter.
Second,About launch (elevation) angle
The antenna's emission angle mainly includes the horizontal emission angle and the vertical emission angle. In this section, we only discuss the horizontal emission angle (that is, the "emission elevation angle" that we often call in short-wave communication).
For short-wave communication, you must have some common sense of launch elevation angle and lobes to play. The landlord has analyzed it thoroughly. Here is a common way to describe it. The smaller the antenna launch angle, the more the jump jump distance through the ionosphere. Long-distance, suitable for long-distance communication. Generally, an antenna with an emission elevation angle of less than 30 degrees is suitable for long-distance DX communication. Inside) Connect.
We will find that the comprehensive effect of domestically transmitted high-elevation inverted V antennas is often better than that of high-gain Yagi antennas, and the tilted antennas have higher elevation angles. Usually, short-wave communication within 500 kilometers of blind areas will be used.
My personal experience: The launch angle of 30-60 degrees is suitable for domestic short-range communication, the launch angle of less than 30 degrees is suitable for long-distance DX, and the launch angle of less than 20 degrees is suitable for hunting, such as the east coast of South America.
The height of the antenna has a great relationship with the transmission elevation angle (gain). By default, the design height of the antenna is 1/2 wavelength height. For example, a log period short wave with a design elevation angle of 25 degrees (gain 12dbi) For antennas, if the installation height is only 1/4 wavelength, the transmission elevation angle may become 40 degrees, and the gain will be reduced to about 9dbi; if the installation height reaches 1 wavelength, the transmission elevation angle may become less than 20 degrees, and the gain Will increase to more than 13dbi.
A well-matched competition base usually uses a lifting tower to install directional antennas. This is not only due to wind protection, but the main factor is that participants can change the antenna gain and launch elevation angle according to the distance of the connected destination and the height of the antenna. , To achieve the purpose of connecting different regions.
About the lobe, the landlord said it very clearly. Generally, the height of the short-wave antenna is greatly related to the number of lobes. When the height is greater than 1/2 wavelength, the lobe will increase. It becomes sharp, and multiple sharp lobes are a good thing for the DX caller, and usually have a good harvest. The beach owner can easily do it. In this way, we usually joke that "seeding in specific areas" .
Multi-lobes are divided into horizontal multi-lobes and vertical multi-lobes.
2. Ultrashort wave (U / V section)
In the U / V section, the vertical polarization method is usually adopted and the line-of-sight propagation. The emission angle generally has two meanings, one is the horizontal emission angle, and the other is the vertical emission angle.
The omnidirectional GP antenna's vertical emission angle is 360 degrees, and the horizontal emission angle is different due to different gains. The greater the gain, the smaller the horizontal emission angle. If it is a fiberglass antenna with a gain of 10dbi, the horizontal emission angle is about 25 degrees. U / The V-segment GP antenna changes the gain mainly by changing the radio wave density in the horizontal direction.
The log-periodic antenna has a strong directivity, and the vertical emission angle has the largest relationship with the number of elements of the log-period antenna, followed by the horizontal emission angle, a 12-element U-section Yagi, the vertical emission angle is about 30 degrees, horizontal With a launch angle of 35 degrees, the U / V segment log period antenna mainly changes the gain by changing the vertical wave density.
For using U / V segment relays, it is necessary to understand the vertical and horizontal launch angles.
In order to ensure the short- and medium-distance relay effect, the low-gain FRP antenna (approximately 6DBI) is generally , the electrical and physical properties are not allowed to increase the unit, and second is the high-band Yagi, such as 6 meters wave, 2 meters wave, etc. The difficulty and cost of the array are very low. The third is a high-bandwidth log-period antenna. The 14-30MHZ log-period antenna needs to increase the 3dbi gain by about 2.5 times. The main beam will be too long and the physical performance cannot be guaranteed. , So the cost of making an array is lower.
Question 2: Use two 4-unit Yagi in different directions, but use one steering gear.
This question is a bit complicated. Before answering this question, I gave two examples above. The TV receiving antenna array and the cellular mobile antenna array. To achieve the combined power split control of the antenna array in different directions, it will bring a lot of vice. As a result, only cellular mobile has truly solved this problem through digital control technology. Our amateur radio does not recommend this method unless you have a large amount of capital or huge technical strength to develop a powerful signal distribution control system.
However, if I have two Yagi like you, it is not bad to try.
Question 3: I want to strengthen the 20-meter band performance by adjusting the antenna system during the game.
This problem becomes simple. As a competition radio station, the most effective way is to configure a 10 to 40 meters electric liftable tower, adjust the height of the tower, change the antenna gain and elevation angle according to the needs of the connected destination, the tower is an antenna gain adjuster , Very effective.