In the wireless microphone system, the wireless signal of the microphone is transmitted to the air by the transmitting antenna, and the receiving antenna collects the signal into the receiver in the air. It can be seen that the antenna is a window for transmitting and receiving wireless signals, and the transmission distance and signal stability are in the transmission distance and signal stability. The function of the antenna is very important. The design of the detachable antenna input device is adopted, so that the user can select different types of antennas to be installed according to the actual use needs of the antenna type and characteristic specifications, so as to achieve the best receiving effect.
The main characteristics of the antenna are described below:
1. Frequency of use
To select the antenna of the wireless microphone receiver, first of all, you need to pay attention to the frequency of use of the antenna. This specification is usually marked as the frequency range of use. It is the so-called "bandwidth". When selecting an antenna, pay attention to the carrier frequency of the receiver. The radio signals received by such an antenna can be effectively transmitted to the receiver within the indicated bandwidth. The length of a typical antenna is inversely proportional to the frequency of use, so antennas suitable for VHF systems are significantly longer than UHF systems.
2. Antenna impedance
The impedance specifications of the antenna are generally 50 Ω and 75 Ω. Therefore, an antenna with an impedance of 50 Ω must be selected to achieve the best match in signal transmission. The characteristic index is usually the input reflection coefficient or the voltage standing wave ratio (VSWR). It is shown that an antenna with good impedance characteristics generally has an input reflection coefficient of less than -10 dB or a voltage standing wave ratio of less than 2:1.
3. Antenna gain
The gain of the antenna is the ability of the antenna to transmit or receive signals. The gain value is obtained relative to a single isotropic radiator. The unit of the antenna gain is expressed by dBi, where "I" represents single point radiation. Body, is a virtual sphere that can uniformly transmit or receive signals in all directions. A basic dipole antenna (Dipole), the theoretical maximum gain value is about 2.15 dBi, because the gain of the antenna design usually has a certain degree of concentration, and will get a value greater than 0 dBi, if in design It is said that the gain is concentrated in a certain direction, which is called Directional. The narrower the angle is, the higher the gain is, but the gain in other directions will be relatively fading. The user must pay attention to the directivity of antenna when installing.
4. Antenna polarization
In practical use, polarization is a characteristic that is easily overlooked by users. According to its electric field distribution ratio, it can be roughly divided into linear polarization and circular polarization.
Linear polarization can be divided into vertical or horizontal polarization depending on the mode of the device, and the circular polarization depends on the direction of the rotation of the electric field, showing a right-hand circle or a left-hand circular polarization. The common antennas are almost all linear polarizations, such as single-pole antennas and coaxial antennas; circularly-polarized antennas require special structural design, and in fact, approximate elliptical polarization. The polarization relationship between the receiving and transmitting antennas directly affects the quality of the received signal.
If the wireless microphone receiver antenna is fixed to vertical polarization, and the transmitter is horizontally polarized due to the user's swing, the receiver signal will have a very large fading at this moment, resulting in unstable reception signal quality, especially When the environment is more empty, the amplitude of the signal will be larger, which will eventually lead to intermittent sound breaks. If a circularly polarized antenna is used, the signal can be stably received for the vertical or horizontally polarized signal, and this phenomenon can be effectively avoided, so that the signal does not largely fading in an instant.
5. Antenna radiation pattern
In a complete antenna product specification, the antenna field type is indispensable. It helps the user to understand the angle and direction of the antenna at the minimum value of the gain (Null) and the main beam. The antenna field pattern contains the vertical radiation surface. (Vertical pattern) and horizontal pattern provide important reference indicators when the device antenna is used.
The difference between Omni-directional and Directional antennas is that the standard omnidirectional antenna has a receiving angle of 360 degrees. The angle of the antenna device does not need to be adjusted. The directional antenna is based on the 3 dB beamwidth. That is, the antenna gain attenuates the angular range and directivity of 3 dB from the maximum value, and the user can choose according to the application environment.
For example, when there is no specific direction between the microphone and the receiver, and the environment is used in a close range, the omnidirectional antenna can be selected; when used on a professional stage at a long distance or in a specific direction, a directional antenna is usually selected, and a better one can be obtained. Receive signal quality and avoid interference signals in other directions.
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