The signal transmission of the walkie-talkie is affected by many factors. VHF and UHF have different call characteristics due to different frequency characteristics. The UHF frequency has better penetrating power and the diffraction is worse than VHF, so it is more suitable for urban use. Due to the lower VHF frequency, the diffraction is better, and the poor penetration is more suitable for the plain area.
V segment (144.00 ~ 148.00MHz)
This is a typical VHF band and is a very active local mobile communication band.
The signal ionosphere in this frequency band basically does not produce reflection. The radio wave is mainly transmitted by direct wave line-of-sight. In the transmission, there is a building room or a mountain body, which will generate reflected waves. Therefore, it can only be used for short-distance communication. Antennas in this band are produced by amateur radio enthusiasts with a variety of high-gain directional and omnidirectional antennas, on-board mobile whip antennas and compact handset antennas.
The interference of the V segment mainly comes from the base stations such as the cordless telephone and the BP machine. This frequency band is the dedicated frequency band of our HAM, and the U segment is the shared frequency band.
U segment (430.00～440.00MHz)
In the UHF band, the direct wave propagation is more severe than the V segment, and the U segment penetration force is better than the V segment, so there are more U segments in the high-rise buildings. However, at the same time, the attenuation of air is larger than that of the V segment, which is not suitable for long-distance communication.
When using longer cables, consider the attenuation of the signal from the cable. Due to the high frequency and low noise of this frequency band, the antennas of various small and full-featured frequency bands that various manufacturers are competing to launch can be made relatively small and can be set in the car. Therefore, mobile communication in this frequency band is very active.
In order to solve the problem of close communication distance, many amateur radio enthusiasts set the relay station at a high position, and by using the forward differential signal, the communication range can be greatly increased, and the enthusiast can use only a small power and a simple antenna. Remote station QSO.
In the unstable seasons such as summer, an abnormal propagation phenomenon called "atmospheric waveguide" is often generated. The electric wave is refracted back and forth between the three layers of atmospheric temperature, and the attenuation is transmitted to the far side with little attenuation. There are also phenomena such as meteor remnant reflection and tropospheric scattering, which will also cause the propagation of radio waves in this band beyond the line of sight.
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