The classification of wireless microphone
According to different definitions, wireless microphone (wireless microphone) can be divided into many different types of.
1, according to the transmitting frequency, a. FM wireless microphone: commonly known as FM refers to FM 88-108MHz international FM radio frequency band. The early consumer wireless microphone is received by FM radio. It has simple system and low cost, but because of its use, it can meet the requirements of professional quality. At present, it can only be a toy for children or students. B. VHF wireless microphone: also divided into two types of low frequency and high frequency section, the former uses the VHF50MHz frequency band, because the frequency is low, the use of antenna length is too long, and the most easy to be disturbed by all kinds of electrical clutter, so this type of product has been replaced by the high frequency section and gradually disappear from the market. The latter uses the VHF200MHz frequency band, because the frequency is high, the antenna is short, even can be designed into the hidden antenna. It is convenient, safe and beautiful. The interference of the electric clutter is greatly reduced. The circuit design is very mature and the price of the parts is low, so it has become the hot machine in the current market.
2, according to the way of reception: A. automatic radio receiver wireless microphone system (True diversity receiving wireless system): due to the physical phenomenon of "dead angle" (Dead-point) will produce the sound output of the receiver in the electric wave public opinion, produce intermittent or unstable missing points, in order to solve this defect, professional use The Automatic switching diversity receiving must be used to improve the aircraft's dual antenna and dual tuner. B. non automatic radio receiver wireless microphone system (Non-diversity receiving wireless system): because the circuit design of the above model is complex and precise, the assembly is difficult and the cost is high, the general low price model does not adopt the design of automatic selection, so it can not eliminate the shortcoming of the sound interruption in the use of the wireless microphone. Of course, this type of aircraft can not meet the basic requirements of professional occasions.
3. According to the oscillation mode, the A. quartz locking (Qualtz locked) machine is a standard circuit design for wireless microphone. This type of microphone and receiver only use a single frequency pairing, and can not change or adjust the frequency of use. B. phase locked frequency synthesis (PLL Synthesized): in order to avoid the interference of other signals in the use of the wireless microphone in use, or to use multiple phones at the same time, it is necessary to change the channel at any time at any time, so the PLL circuit is used to achieve this function.
4, according to the number of receiver channels: A. single channel: only one channel is assembled in a receiver's chassis for a non automatic or automatic selection receiver. The former has almost no market in Taiwan, but the market is the cheapest in the export market, but it is a (large color). The latter is simple and stable, and is suitable for multi-channel use in professional occasions and avoids signal interference. B. dual channel: in the case of a receiver, a non automatic or automatic receiver of two channels is assembled to make full use of the space of the chassis to reduce the cost. The former is the so-called "Asian fighter" model, because the design is simple, and become the main type of low price manufacturers in Taiwan. The latter because of the complex mechanism and circuit, the internal interference processing and the antenna mix matching is not easy, only a small number of manufacturers in the production of professional machine models. C. multichannel type: in a receiver's chassis, more than four channels are installed, most of which are designed by modular receiver module. It is mainly suitable for the use occasion of mounted professional aircraft.
As wireless phones are being used more and more in different situations, no matter how advanced wireless transmitter and receiver technology has a wireless microphone, it will result in the instability of signal reception because of the particularity of the use. An overview of the transmission and reception of wireless phones first let us get a general understanding of the transmission and reception of the wireless microphone. Most of the wireless phones we often use are working in the VHF band or UHF band, and the radio signals of the VHF and UHF bands are collectively called radio frequency signals. (RF), the UHF band makes more use of direct radiation electromagnetic waves. The VHF band, in addition to the direct radiation, also uses a part of the electromagnetic wave of refraction and diffraction. Therefore, the transmission distance can be farther under the same transmitting power and propagation conditions. With the continuous mastery of VHF Technology, the scope of application is becoming wider and wider. This is often full of VHF frequency electromagnetic waves in our daily life environment. Commonly used interphones usually work in the VHF band, so if we use the VHF band wireless microphone, the opportunity to be disturbed will be much larger. And UHF technology is not yet mastered by many manufacturers, and also because of its circuit. This is much more expensive than VHF, so the scope of application is not as wide as VHF, and the opportunity to be disturbed by UHF wireless microphone will be much smaller. In view of this reason, most high-end wireless phones will use UHF technology. The transmission characteristic of UHF is more direct transmission by direct radiation, and of course it also has certain penetration ability. But if you encounter an object with the absorption characteristics of the electromagnetic wave (such as a metal material), it will be powerless. We can use the radio microphone antenna as a light emitting body that fires light around it and the receiver antenna of the wireless microphone can be used as a sensor of light as a wireless microphone to launch the UHF signal. When the transmission power is generally 10mW (according to the international electromagnetic laws and regulations), the transmission distance of the UHF signal is like our flashlight, which is getting weaker with the increase of distance, so the wireless microphone has a problem of transmitting distance, and our wireless microphone receiver is like a sensor, as a receiver. The system must have a received inductive value - - the receiving sensitivity (SQUELCH) that we often say. It is like the threshold switch that we often use in the professional sound engineering. Only a signal with a power greater than the threshold can enter the receiver's demodulation circuit, and thus it can be known by adjusting the sensitivity. The size of the degree can also regulate the length of the receiving distance. But the sensitivity of adjustment may also bring some drawbacks. When the sensitivity is too high, it is like when the windows in our home are too big. Not only the fresh air comes in, but also the mosquitoes and flies are easy to come in, that is, when the sensitivity is too high. It is easy to be disturbed by some weak noise outside (for example: mobile phone, high frequency interphone), and vice versa. When we use sensitivity adjustment, we do not greedy for large receiving distance, but eat food, tailor, depending on the actual situation. Here everyone is UHF wireless. The launch and reception should have a certain understanding. Next we will discuss the solutions for the stable reception of wireless microphone under several special circumstances.
1. In the performance of the few people when the microphone is no problem, when people have more frequency, we often do the performance of the friends will encounter such a problem, in the rehearsal process, the microphone has been used well, but the audience, the critical time of the formal performance of the frequency of broken frequency. On the above we talk about the UHF band. The transmission is generally direct radiation, and some can also reach the receiver by penetrating obstacles and refraction, but when we perform in the performance, especially in the outdoor performance, all sides are open space, so the refraction can not exist. In the formal performance, the audience is bound to be many, if the main console is in the audience. The receiver's antenna may be blocked by the audience. Although our UHF signal can penetrate a part of the audience's body to reach the receiving antenna, the more the objects are penetrated, the more the attenuation will be, the more it can reach the antenna, its work rate may not be enough to open the sensitivity of the receiver. Degree "gate", which caused the phenomenon of breaking frequency.
There are several ways to solve this problem:
1.1 If we use a single set of wireless microphone, and this microphone has a sensitivity adjustment function at this time, we first adjust the sensitivity of the receiver to the maximum. If there is a frequency breaking phenomenon, the microphone can be placed above the audience (preferably at the stage); or the microphone antenna is extended to the outside, but we need it at this time. An auxiliary device, the antenna amplifier, is caused by some gain loss during the extension of the antenna cable, and the addition of the antenna amplifier can compensate for the gain loss caused by the coaxial cable.
1.2 If we use multiple sets of wireless phones, we can't put so many wireless phones on the stage, and if you have to pull a lot of antennas above the console, it doesn't seem to be a real thing. But in the end we have a way to solve these problems, and we can add another kind of device - Wireless. The microphone antenna splitter, this device can use an internal matching circuit to allow a few sets of microphone to share an antenna and then match the antenna amplifier, and then find two higher microphone supports to support the antenna amplifier, so that we have solved the problem of the stable reception of multiple sets of microphone at the same time.
2.When the microphone is moved by the microphone, the range of the receiver can not meet the needs. When we do large concerts in the stadium, we often have to build a large stage and build a few layers of high lamp frames, all of which are not conducive to the use of the wireless microphone. It is known that the standard transmission power of the wireless microphone is 10mW. The transmission distance is very limited because of the transmission in the air and the barrier and absorption of some materials, and the receiver sensitivity setting will also have a certain influence on the receiving distance. The distance of the general wireless microphone is: the distance of 50~120 meters. If the environment is used with very strong electromagnetic interference or electromagnetic shielding, the distance may not exceed 50 meters. In summary, the wireless microphone will still receive a great test in large performance. But the problem of interruption can be avoided to a large extent by the combination of antenna splitter and antenna amplifier. If we use a wireless microphone within four sets, we need only one antenna splitter and two antenna amplifiers to make up a combination of figure and 7 styles. It's just that we have to use coaxial cable to pull the antenna amplifier as close to the stage as possible. If we can fix it on the stage, it will be better. The installation of the antenna below ensures that the transmitted signal is not obscured in most cases and thus ensures a stable reception. In this way we can also make some trade-offs, if we want to ensure stronger reception stability, the distance between the two antenna amplifiers is kept as much as possible between the 50M~100M. Because we can use the automatic microphone function to select the strongest one of the two antenna amplifiers as the receiving signal, and in the other case, if we are going to have a long enough distance, we can adjust the distance between the two antenna amplifiers to 100M~180M. The receiver is received by the single side antenna of the microphone, so the receiver can reach about 400 meters in theory with the receiver diameter (the center of the two antenna amplifiers), but this is the distance we have changed at the expense of certain stability.
3.There is another possibility that when we do the project, we will find that when we work in some high secrecy units, we will suddenly find that the distance of the wireless microphone is more than ten meters. This is because some units have installed electromagnetic shielding on the walls of buildings in order to prevent the leakage of electromagnetic waves. So, the signal of our wireless microphone can't penetrate these walls, which affects the firing distance. The way to solve this problem is simple. We just use a coaxial cable through the wall, connect the antenna amplifier at one end of the signal and connect the other end to the wireless phone, so it will not leak the use side. The electromagnetic wave signal has achieved the purpose of stable reception of the microphone.
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