As a branch of antenna, vehicle antenna has similar working properties to other antennas, and will encounter similar problems in use.
1. First, what is the relationship between the installation position of the vehicle antenna and its directivity?
In theory, the vehicle antenna installed on the car has no directional direction in the horizontal direction, but because of the irregular shape of the car body and the antenna installation position, the actual installation of the mobile antenna has some directivity, and the performance of this directivity is different from that of the directional antenna. The directional nature of car antennas is irregular and varies from car to car.
If the antenna is installed in the middle of the roof, the antenna radiation in the front and rear directions will be slightly stronger than the left and right directions. If the antenna is mounted on one side, the radiation effect is slightly better on the opposite side. Therefore, we sometimes find that when we go the same way, the communication effect is OK, but when we go back, the direct communication effect is very different, because the antenna radiation effect on both sides of the car is different.
2. Why are the signals of direct communication intermittent in the application of V/UHF mobile?
Usually, V/UHF frequency waves have multiple paths during transmission, some reach the receiving point in a straight line, and some reach the receiving point after reflection. When the wave passing through direct beam and reflected wave are in the same phase, the superposition of the two waves results in the mutual strengthening of the signal strength. When the direct and reflected waves are in opposite phases, their superposition cancels each other out. As the distance between transmitting and receiving of a vehicle radio station changes constantly when it is moving, the intensity of the radio wave also changes dramatically, which is reflected in the intermittent signal.
With the different moving speed, the interval of alternating change of radio wave intensity is also different. The change rule is: the higher the working frequency, the shorter the wavelength, the faster the moving speed, the higher the frequency of intermittent signal. Therefore, when the signal discontinuity seriously affects the communication, you can slowly reduce the moving speed, find the place where the superposition signal is the strongest, stop the car for direct communication, and then go back on the road.
3. The vehicle antenna vertical installation or oblique installation is better?
Many vehicles use vertical antennas for the following reasons: the first is that the vertically polarized antenna theoretically has no direction in the horizontal direction, so that the vehicle radio in mobile use does not have to bother to align the direction of the antenna; Second, the vertical antenna can use the metal shell as its virtual oscillator, so that when the vertical antenna is in actual use, only half of the manufacturing can be installed, and the rest can be replaced by the car body, which not only reduces the cost, but also facilitates the installation and use. The third is that the vertical antenna occupies a small position, and the wind resistance of the antenna is relatively small, which is conducive to fast movement.
From this point of view, the part we have installed is actually only half of the vertical antenna. Therefore, when the antenna is mounted diagonally to one side, the radio waves emitted by the antenna are not vertically polarized waves, but a mixture of vertically polarized and horizontally polarized waves. If the receiving antenna of the other side receives vertically polarized waves, The strength of the received signal is reduced (with less horizontal polarization), and vice versa for the received signal. In addition, the oblique antenna makes the radiation unbalanced, which is manifested as the forward radiation of the antenna is greater than the backward radiation, resulting in directivity.
4. How to solve the noise interference brought by the vehicle antenna when receiving signals?
Antenna noise interference is generally divided into external interference and internal interference two types. External interference is the interference signal received from the antenna outside the car, such as industrial interference, urban electrical interference, other vehicle radiation interference and sky interference, such interference solution is the best way to stay away from the interference source. Usually, FM mode in V/UHF band has a strong ability to resist this kind of interference. After the signal can be turned on, the internal limiting circuit of the machine can eliminate the interference. For internal interference, you can simply test and listen to a relatively weak radio station. If the interference is not large, it indicates that there is no problem with the interference of the vehicle system. If there are other internal distractions, using an on-board transceiver will solve most of the problems.
Post time: Nov-30-2022
