Digital cellular mobile communication system testing (mobile station tests) To ensure the service quality of the mobile communication system, the electrical performance of the mobile station is measured before it is used in the network Mobile stations: Mobile stations include car mounted, handheld, portable, and fixed types for ships and special areas. Initially focused on car mounted devices, handheld devices developed rapidly due to their small size, light weight, convenient portability, and low price. A mobile station is the part of a mobile customer device, which consists of two parts: a mobile terminal (MT) and a customer identification card (SIM). A mobile terminal is a "machine" that can complete voice coding, channel coding, information encryption, modulation and demodulation of information, and information transmission and reception Test items: mainly include performance testing of transmitters, receivers, duplexers, and antennas. 2.1 The testing content of the transmitter, receiver, and antenna is the same as that of the base station. (1) The transmitter performance includes frequency tolerance, spurious emission, adjacent channel power, RF output impedance, pre emphasis, modulation characteristics (including rated frequency offset and maximum allowable frequency offset, rated effective frequency offset with voice, maximum allowable frequency offset, frequency offset of digital signals; frequency offset of out of band continuous single tones; frequency offset of signaling tones. Limiting characteristics of modulators. Residual modulation, etc.) Audio characteristics (including audio bandwidth, audio response, audio impedance, echo attenuation, harmonic distortion coefficient, voice processing, and relative attenuation of audio intermodulation products), receiver performance including sensitivity, adjacent channel selectivity, intermodulation suppression ratio, co channel suppression, spurious response suppression, blocking, conducted stray radiation, RF impedance, de emphasis, amplitude modulation suppression Audio characteristics (including audio bandwidth, audio response, audio impedance, echo attenuation, harmonic distortion coefficient, relative attenuation of audio intermodulation products, and audio output power). (2) The antenna characteristics include polarization mode, directional pattern, gain, input impedance, and standing wave ratio The polarization of an antenna refers to the direction of the electric field intensity formed during antenna radiation. When the direction of the electric field intensity is perpendicular to the ground, this radio wave is called a vertically polarized wave; When the direction of the electric field intensity is parallel to the ground, this radio wave is called a horizontally polarized wave A directional graph is a characteristic curve that represents the directionality of an antenna, that is, a graph of the antenna's ability to transmit or receive electromagnetic waves in various directions. The practical antenna is located in a three-dimensional geometric space, so its directional pattern should be a three-dimensional one. In this stereogram, there are different directional maps due to the different cross-sections taken. The most commonly used are directional maps in the horizontal plane (i.e. directional maps in a plane parallel to the earth) and directional maps in the vertical plane (i.e. directional maps in a plane perpendicular to the earth). Some professional books also refer to equatorial or meridional directional maps. The performance of a duplexer includes insertion attenuation, isolation attenuation, input and output impedance, and standing wave ratio. (1) Input impedance refers to the equivalent impedance at the input end of a circuit. Add a voltage source U to the input terminal and measure the current I at the input terminal, then the input impedance Rin is U/I. (2) The standing wave ratio, also known as the voltage standing wave ratio, is the maximum voltage amplitude Vmax formed by the addition of voltage amplitudes at the same phase of the incident and reflected waves, forming a wave belly; The voltage amplitude decreases to the minimum voltage amplitude Vmin where the incident wave and reflected wave phases are opposite, forming a wave node. The amplitude values of other points are between the antinodes and nodes. This type of composite wave is called a standing wave. The standing wave ratio is the ratio of the voltage amplitude Vmax at the antinode of the standing wave to the voltage amplitude Vmin at the nodal point