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Analysis of wireless microphone products

Publisher: AdministratorTime:2018-2-3 16:39:48
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1. Wireless microphone

A wireless microphone, or wireless microphone, is a sound device for transmitting sound signals, consisting of two large parts of a transmitter and receiver, often referred to as a wireless microphone system.

The transmitter is powered by a battery, and the microphone converts the sound to an audio signal, which, after being processed by an internal circuit, sends radio waves containing the audio information to the surrounding space.

Receiver generally by the mains power supply, by the receiving antenna to receive radio waves from the transmitter, through internal circuit processing, to extract the audio signal, and through the output signal to sound reinforcement system, audio signal wireless transmission. A receiver inside usually contains 1 set, 2 sets or 4 sets of receiving circuit, receiving respectively 1, 2 or 4 microphones wireless signal, respectively called "yi tuo", "yi tuo 2" or "yi tuo four" models. One of them is the most common.

The wireless microphone is essentially a one-way wireless communication system.

1.1. UHF frequency band

Wireless microphone system is transmitted by radio waves of sound signal equipment, according to the wireless microphone and receiver between sending and receiving of high and low frequency, it can be divided into different frequency bands, general and commonly used FM, VHF, UHF band.

FM frequency band refers to the 88-108mhz frequency band used in public FM broadcasting and its nearby frequency band. Generally, only some simple wireless microphone products are used in this frequency band.

VHF frequencies, according to the division of international standards, is 30 ~ 300 MHZ band, FM frequencies described above is included in the VHF frequencies, just because of its close to public frequency modulation (FM) radio frequencies, so called the FM band. VHF BAND wireless microphones are often called VHF HIGH BAND (VHF HIGH BAND) with a range of 170~260MHz.

UHF frequency band, it is to point to 300 ~ 3000 MHz band, wireless microphones usually use 400 ~ 830 MHz band, less use of more than 830 MHz band, because 830 ~ 960 MHz band GSM and CDMA mobile phone interference, more than 960 MHz band diffraction ability gradually becomes poor, so now the most popular in the international UHF frequency is 800 MHz band (740 ~ 830 MHz).

2. Several terms

To understand the performance characteristics of wireless microphones, it is necessary to understand the basic terms of the wireless microphone and the specific meaning of the main performance indicators. In addition to the same audio indicators as wired microphones, the wireless microphone has some unique terminology and performance indicators.

Noise: when the receiver of the wireless microphone is not receiving the signal or the signal is weak, to avoid the output noise, the output signal will be automatically cut off. This function is called Squelch. If there is no noise, or if the noise is not good, the loudspeaker will make noise when there is no signal or weak signal. Noise can affect the quality of sound, damage the atmosphere, and even damage the amplifying equipment.

Dead point: also known as dead zone or blind area. In the process of moving the wireless microphone, the receiver receives signals that vary greatly depending on the distance, relative position, or obstructions. In normal use of certain positions in the distance, the weak signal will cause the noise in the receiver to operate, and the output signal will be cut off. After leaving the position, it can receive and output normally. The location is known as the dead or blind spot. When the wireless microphone is close to or above the effective distance, it is inevitable that there will be a dead point. If the circuit design is reasonable, there will be no sound when there is a dead point. If the design or manufacturing is not good, then there is not a normal sound but a noise.

Diversity reception: the wireless microphone receiver can receive the signal from the same wireless microphone from the two antennas, and select the stronger signal through the internal circuit. This method can greatly eliminate the dead zone, avoid mute or produce dead noise. There are two ways to receive the diversity: the antenna diversity and the central set.

In antenna diversity in the way, there are two receiving antenna, a set of control circuit and a receiving circuit, when the work of the received signal weaker, the control circuit will automatically switch to use a different antenna.

In the way into the diversity, in addition to the two antenna and a control circuit, there are two sets of the complete receiving circuit, working at the same time, by tracking switch control circuit, good output audio signal all the way. This approach is better than the previous one because it keeps track of stronger signals, but the circuit is complex and expensive. This kind of diversity is often called double tuning, true diversity, etc. Usually in live performance, studio and other important occasions, it is necessary to choose a double - tuned real diversity product, to ensure that the practical operation distance does not produce a dead point.

Multi-channel: general wireless microphone, its carrier frequency is fixed, the user can not change in the use process. Because the wireless microphone sound signal is sent by radio waves, so when the working environment and its carrier frequency in the same or close to the outside world signals, interference occurs, reduce receiver receiving distance, output noise, even less than the phone reception.

In view of this situation, the manufacturer has developed a multi-channel wireless microphone system. The transmitter (wireless microphone), and the work frequency of the receiver are adjustable, so users can meet foreign frequency interference, change the carrier frequency system, to avoid interference signals and the normal work; In addition, if multiple wireless microphones are used in the same field, it is also convenient to adjust each microphone to different working frequencies so that they do not interfere with each other and coordinate work. Most of the wireless microphones used in large-scale professional stage performances are multi-channel systems, with 8 channels, 16 channels, and even more channels, the most common of which are 16 channels. The multi-channel system generally adopts the phase-locked loop (PLL) frequency synthesis technology, microcomputer control technology and other related technologies. Its production technical requirements, equipment requirements, production costs and product performance are far higher than other ordinary models.

Some products on the market at present, is a fixed frequency, but the same model of a batch of products, also can produce products into different frequency, the user can choose when to buy, but after the purchase, in use can not adjust the working frequency, some manufacturers will also be nominal "multi-channel" for this kind of situation, "32 channel can be arbitrary choice", this is not accurate, or deliberately misleading. There are several ways to distinguish this situation. One is to observe whether there are switches or buttons on the receiver panel. The second is to see whether its publicity materials or instructions are marked "adjustable frequency" and "user adjustable channel"; Three is the actual operation, see if adjustable.

Signal-to-noise ratio: the ratio of the original audio signal to the noise signal in the output signal when the receiver receives a signal of a specified strength (usually 60dB), in decibels (dB). The larger the value, the cleaner the signal, the better the machine performance.

Receiving sensitivity: in a radio or intercom, the receiving sensitivity refers to the size of the minimum rf signal to be entered when the receiver outputs a signal of signal to noise ratio. The smaller the value, the higher the receiving sensitivity of the receiver. In the wireless microphone, should be based on critical noise receiver when the value of input rf signal, because when the input signal is less than the static noise, the receiver is in a state of noise, is out of the output signal.

For example, a product receiving sensitivity labeled "- 90 DBM," said the line of the input signal is lower than 90 DBM (7 mu V), the receiver will enter a state of noise, such annotation can accurately response of the receiver to receive ability.

Some products, its sensitivity index USES similar radio, walkie-talkie, labeling methods, such as labeled "2 mu V / 12 db", its meaning is the line of the input signal is 2 mu V (101 dBm), receiver output signal can reach 12 db SNR. The signal-to-noise ratio of the wireless microphone is much higher than that of 12dB, so this method cannot correctly express the receiver's receiving ability.

Rf output power: the magnitude of the energy used to transmit signals to space by a wireless microphone transmitter, usually in milliwatts (mW), usually between 5 and 50 mW.

Effective working distance: the maximum distance the wireless microphone can transmit normally. The parameters indicated on the general product are specified in the open or ideal conditions. Because the actual transmission distance of the wireless microphone is affected by the actual environment, it cannot be clearly marked. Only in the open or ideal conditions of indicators, can provide reference, and can be compared with each other.

Actually, want to measure the abilities of transmission of wireless microphone, to see whether the transmitted power and critical noise when receiving sensitivity, these two indicators after converted into the same unit, the greater the difference, is equally effective working distance away with the environment. It is possible to estimate and compare the effective transmission distance of different products with the combination of the receiver and the diversity. Generally speaking, the effective distance of the diversity receiver is greater than that of the non-diversity receiver, and the receiver of the amplifier is larger than the receiver of the antenna diversity.

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