Radio signal transmission.
Radio signal transmission
Radio signals, which are the basis, in particular, of satellite communications and other types of communications, are electromagnetic waves. The communication system uses various types of radio signals to transmit information through the air from one point to another.
Radio signal transmission
The radio signal is transmitted from the antenna of the transmitting station to the antenna of the receiving station. Radio signal transmissionis carried out due to several factors. The signal supplied to the antenna is characterized by amplitude, frequency and phase. By changing these parameters, it is possible to transmit information via radio signals. Amplitude determines the intensity of the radio frequency signal. A measure of amplitude is power, which is similar to the effort expended by a person riding a bicycle a certain distance. Power is the amount of energy required for a signal to travel a certain distance. If power increases, then the communication range also increases. Radio signal transmission occurs through the air, which causes a decrease in its amplitude. In the absence of obstacles, radio signals experience losses in free space, they are one of the reasons for signal attenuation, and radio signal transmission loses its previous quality. The signal amplitude decreases exponentially as the distance between the transmitter and receiver increases. Exponential attenuation of the modulated signal is caused by the atmosphere if it is propagated far enough from the antenna. Therefore, the signal must have sufficient power to cover the required distance and then have a level sufficient for the receiving device to distinguish it from the noise.
Radio signal amplifier
The receiver's ability to pick up a signal also depends on the presence of other radio frequency signals. In other words, a radio signal amplifier is needed to improve the quality of signal transmission. The amplifier's function is to increase the power of the radio station supplied to the external antenna without distorting the signal structure itself. Radio signal amplifiermakes changes to the characteristics of the equipment only when working on transmission. The sensitivity of the radio station is limited not by amplification, but by the noise level (both its own and on-air), i.e. the ability to isolate a useful signal against the background of interference. Radio signal amplifieris included in the gap of the antenna cable, i.e. between the radio station and the external antenna and is connected with thick wires to a powerful power source. The length of the high-frequency coaxial cable connecting the radio station and the amplifier can be any, and special attention should be paid to the quality of the sealing of the connectors at its end and at the end of the antenna cable. Experts recommend using a radio signal amplifier with an output power of 100 — 200 watts. In this case, you can expect an increase in the communication range, with less power. The antenna connected to the amplifier must be well tuned (have an SWR close to 1) and maintained in order, then you can not worry about the further condition of the amplifier. Thinking about buying a radio signal amplifier, it is worth paying attention to such a characteristic as phase. Phase corresponds to how far the signal is from some starting point. Traditionally, it is accepted that each signal cycle corresponds to a phase rotation of 360 degrees. For example, the phase shift of a signal can be 90 degrees, which means that the phase shift is equal to a quarter (90/360 = 1/4) of the full signal cycle. The phase change can be used to transmit information. Thus, a phase shift of a signal by 30 degrees can be represented as a binary 1, and a phase shift of 60 degrees — as a binary 0. An important advantage of representing data in the form of phase shifts is the reduction in the effect of signal attenuation as it propagates through the medium. Attenuation usually affects the amplitude, not the phase of the signal.
Types of Radio Signals
The most productive area of application of radio signals is navigation. The principle of operation of the satellite system is based on just such a mechanism. Within the satellite system, different types of radio signals are distinguished. For example, in the GLONASS system, each regular NSC in the OG constantly emits noise-like continuous navigation radio signals in two frequency ranges of 1600 MHz and 1250 MHz. In the NAP, navigation measurements in two frequency ranges allow ionospheric measurement errors to be eliminated. Each NSC has a cesium AFC used to form the onboard scale (BSHV) and navigation radio signals of 1600 MHz and 1250 MHz. Such types of radio signals, as noise-like navigation signals in the OG of the NSC differ in carrier frequencies. Since the same carrier frequencies can be used for mutually antipodal NSC in orbital planes, the minimum required number of carrier frequencies in each frequency range for 24 regular NSC is 12. Of two mutually antipodal NSC, at least one will be below the local horizon with respect to the space consumer. It is practically impossible to use on a space object one wide-beam antenna capable of receiving navigation radio signals from all «visible» NSC above and below the local horizon. Therefore, in the NSC on the space object the following is used: either one wide-beam antenna for receiving navigation radio signals from NSC located above the local horizon; or several antennas and several receivers for receiving navigation radio signals from NSC located above and below the local horizon. In both cases, the NSC on the space object will perform effective spatial selection of navigation radio signals from mutually antipodal NSC.
Types of radio signals of the navigation system of mutually antipodal NSC with the same carrier frequencies will be reliably separated in the NAP on the space object due to spatial and Doppler selection.
Let's consider some more types of radio signals — narrowband and wideband. The narrowband navigation radio signal of 1600 MHz is formed by manipulating the phase of the carrier oscillation by 180? periodic binary pseudo-random sequence (PSP1) with a clock frequency. By inverting PSP1, time marks (TM) of the onboard time scale (OTS) of the NSC and binary symbols of digital information (DI) are transmitted.
The wideband navigation radio signal of 1600 MHz is formed by manipulating the phase of the carrier oscillation by 180? periodic binary sequence PSP2 with a clock frequency F2 = 5.11 MHz. By inverting PSP2, binary symbols of the digital signal with a duration of 20 ms are transmitted.