What are Wireless Microphones?

The wireless microphone is composed of several pocket transmitters (which can be installed in a pocket and the output power is about 0.01W) and a centralized receiver. Each pocket transmitter has a different working frequency. The centralized receiver can Simultaneously receive voice signals of different working frequencies from each mini-transmitter. It is suitable for occasions such as the stage podium.

wireless microphone

wireless

Do not grab on the head of the wireless microphone to use:

Sensitivity is the ratio of the output voltage to the input sound pressure of the microphone under unit sound pressure excitation, and its unit is mV / Pa. To be consistent with the measurement of the level in the circuit, the sensitivity can also be expressed in decibels.

Means:

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Make a choice

The quality of wireless microphones made in Taiwan has improved significantly due to the increase in consumer requirements: the price has dropped significantly due to fierce competition from manufacturers. Therefore, in order to win orders, some smaller manufacturers are not committed to research and development of more advanced models, but to produce simpler models with lower prices to attract consumers. As the saying goes: "One penny, one penny", consumers often buy products of poor quality because they are greedy for a little cheaper prices. Some consumers may be misled by excessively superstitious brand names or by false advertising by manufacturers. So the money is not worth the fare. How to choose a value-for-money model, first respond to your own requirements

1. Simply connect the negative pole of the 9V battery to the battery case, and extend the transmitting antenna of the wireless microphone through the battery case to increase the transmission distance and prevent frequency cuts and running.

2. The negative end of the 9V battery holder of the wireless microphone is wound into a dense spiral with an enameled wire, which is fixed on the opposite side of the tongue plate of the wireless microphone. Diameter 4MM around the head squashed).

3 Those who have the ability to disassemble the wireless microphone. Pull out the tail by more than two inches, reveal the half-inch multi-circuit board, find the position of the transmitting tube, solder a 1P capacitor (or a few P capacitors and the smallest capacitor) and wind it into a dense spiral with an enameled wire, and fix it in the groove at the rear of the wireless microphone The outer diameter of the spiral is less than the width of the groove, and it is flattened and fixed in the groove. Note: using

Analysis:

The following is the circuit diagram of the FM wireless microphone (Figure 1) . The circuit is very simple and there are no extra components. High-frequency transistor V1 and capacitor

Some film and television sound workers conducted detailed practical tests on several wireless microphones commonly used in daily work. The pickup of wireless microphones is not only related to distance, but also to sound quality, including distortion, noise, interference, and stability.

test

The entire test was conducted in a TV production unit, focusing on the actual needs of TV sound work, such as performance indicators of equipment, working distance mimicking the actual working environment, sound waveform display, and subjective evaluation of sound quality. This article only selects the distance test of the L and S wireless microphones for introduction.

The test method is roughly as follows: In order to place the two sets of wireless microphone receivers at the same point, two

1. A wireless microphone, or wireless microphone, is an audio equipment that transmits sound signals. It consists of two parts, a transmitter and a receiver, and is usually called a wireless microphone system.

The transmitter is powered by a battery, and the microphone converts the sound into audio electrical signals. After processing by the internal circuit, it transmits radio waves containing audio information to the surrounding space.

The receiver is generally powered by the city power. The receiving antenna receives the radio waves from the transmitter. After processing by the internal circuit, the audio signal is extracted and sent to the sound reinforcement system through the output signal line to complete the wireless transmission of the audio signal. A receiver can usually contain 1 set, 2 sets, or 4 sets of receiving circuits, which respectively receive the signals of 1, 2, or 4 wireless microphones, which are called "one-to-one", "one-to-two" or "One for four" model. One of the two models is the most common.

A wireless microphone is essentially a unidirectional wireless communication system.

1.1. Frequency band wireless microphone system is a device that transmits sound signals through radio waves. It can be divided into different frequency bands according to the level of the transmission and reception frequency between the wireless microphone and the receiver. Generally, several frequency bands such as FM, VHF, and UHF are commonly used.

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 use this frequency band.

The VHF frequency band is divided according to international standards and refers to the 30 ~ 300MHz frequency band. The FM frequency band mentioned above is actually included in the VHF frequency band, but it is called the FM frequency band because it is close to the public frequency modulation (FM) frequency band. VHF band wireless microphones mostly use the 170 ~ 260MHz frequency band, which is often called VHFHIGHBAND.

The UHF frequency band refers to the 300-3000MHz frequency band. Wireless microphones generally use the 400-830MHz frequency band. The frequency bands exceeding 830MHz are rarely used because the 830-960MHz frequency band is interfered by GSM and CDMA mobile phones. So the most popular UHF frequency band in the world is 800MHz frequency band (740 ~ 830MHz).

2. Several terminology To understand the performance characteristics of wireless microphones, it is necessary to first understand the basic terminology of wireless microphones and the specific meaning of main performance indicators. In addition to the same audio indicators as wired microphones, wireless microphones also have some unique terminology and performance indicators, which are introduced one by one below.

Squelch: When the receiver of the wireless microphone does not receive a signal or the signal is weak, the output signal will be automatically cut off to avoid output noise. This function is called squelch. If there is no squelch function or the squelch function is not good, noise will be emitted from the speaker. Noise will affect the sound quality, destroy the atmosphere of the scene, and even damage the sound reinforcement equipment.

Dead point: also known as dead zone. During the movement of the wireless microphone, the signal received by the receiver will change due to distance, relative position or obstacles. In some positions within the normal use distance, an excessively weak signal will cause the squelch circuit in the receiver to operate and cut off the output signal; after leaving this position, it can receive and output normally. This position is called a dead point or dead zone.

Diversity reception: It means that the wireless microphone receiver can receive the signal of the same wireless microphone from 2 antennas, and use the stronger one signal through the internal circuit. This method can greatly eliminate the receiving dead zone, avoid dumb noise or generate dead point noise. There are two ways of diversity reception: antenna diversity and mid-amp diversity.

In the antenna diversity method, there are two receiving antennas, a control circuit and a receiving circuit. When the received signal is weak during operation, the control circuit will automatically switch to use another antenna.

In the mid-amp diversity method, in addition to two antennas and a set of control circuits, there are two complete sets of receiving circuits that work simultaneously. The control circuit tracks and switches to output a better audio signal. This method is better than the previous method because it tracks stronger signals at any time, but the circuit is complicated and the cost is high. This diversity method is often called dual tuning, true diversity, and so on.

Multi-channel: general wireless microphone, its carrier frequency is fixed, users can not change during use. Because wireless microphones transmit sound signals through radio waves, when there are external signals in the working environment with the same or close to their carrier frequency, interference will occur, reducing the receiver's receiving distance, output noise, and even not receiving Microphone signal.

In response to this situation, manufacturers have developed multi-channel wireless microphone systems. The working frequency of its transmitter (wireless microphone) and receiver is adjustable, so that users can change the carrier frequency of the system when it encounters external frequency interference to avoid interference signals and work normally; When multiple wireless microphones are used in the venue, each microphone can also be conveniently adjusted to a different working frequency 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 is 16 channels. Multi-channel systems generally use phase-locked loop (PLL) frequency synthesis technology, microcomputer control technology and other related technologies. Its production technology requirements, equipment requirements, production costs, and product performance are far higher than other ordinary models.

Some products on the market are fixed-frequency, but a batch of products of the same model can be produced into products with different frequencies. Users can choose at the time of purchase, but cannot adjust their operating frequency. Some manufacturers are also labeled as "multi-channel", "32 channels can be selected at will", which is inaccurate or intentionally misleading consumers. This situation requires special attention, and there are several ways to distinguish: one is to observe whether there is a switch or button to adjust the channel on the receiver panel; the other is to see whether its promotional materials or instructions are labeled "adjustable frequency" "Tuning channel" and so on; the third is the actual operation to see if it is adjustable.

Signal-to-noise ratio: refers to 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 (generally 60dBV), expressed in decibels (dB). The larger the value, the purer the signal and the better the performance of the machine.

Receiving sensitivity: In a radio or walkie-talkie, the receiving sensitivity refers to the minimum RF signal that needs to be input when the receiver outputs a signal with a specified signal-to-noise ratio. The smaller the value, the higher the receiving sensitivity of the receiver. In wireless microphones, the value of the input radio frequency signal at the time of the receiver's critical squelch should be represented, because when the input signal is lower than the squelch point and the receiver is in the squelch state, the signal is not output.

For example, a product's receiving sensitivity is marked as "-90dBm", which means that when the antenna input signal is lower than -90dBm (that is, 7V), the receiver will enter a squelch state. Such marking can accurately reflect the receiver's receiving capability.

For some products, the sensitivity index is similar to that of radios and walkie-talkies. For example, it is labeled as "2V / 12dB", which means that when the antenna input signal is 2V (ie -101dBm), the receiver output signal can reach 12dB signal-to-noise. ratio. The signal-to-noise ratio of wireless microphones is required to be much higher than 12dB, so this labeling method cannot correctly express the receiving capability of the receiver.

RF output power: refers to the amount of energy transmitted by a wireless microphone transmitter into space, usually expressed in milliwatts (mW), usually between 5 and 50 mW.

Effective working distance: refers to the maximum distance that a wireless microphone can normally transmit signals. Most of the parameters marked on general products are in open or ideal conditions. Because the actual transmission distance of a wireless microphone is affected by the actual environment, it cannot be accurately labeled. Only indicators in open or ideal conditions can provide a reference and can be compared with each other.

In fact, to measure the transmission capacity of wireless microphones, we need to look at the transmission power and the reception sensitivity at critical squelch. These two indicators are converted into the same unit. The larger the difference, the longer the effective working distance in the same environment. Combined with whether the receiver is a diversity type and which diversity mode, the effective transmission distance of different products can be clearly estimated and compared. In general, the effective range of a diversity receiver is greater than that of a non-diversity receiver, and the receiver of the intermediate-amplification diversity is larger than the receiver of the antenna diversity.