Each wireless transmitting device occupies a frequency bandwidth when it is working, just like every car occupies a driving lane. Here, the frequency is like a highway, and the bandwidth is like there are countless driving lanes on a highway. The microphone receiver is like a person waiting on this lane. When the wireless device is working, if other devices use your frequency band. It seems to occupy your driving lane. So people who wait for a car are often not waiting for their own car.
Each wireless transmitting device occupies a frequency bandwidth when it is working, just like every car occupies a driving lane. Here, the frequency is like a highway, and the bandwidth is like there are countless driving lanes on a highway. The microphone receiver is like a person waiting on this lane. When the wireless device is working, if other devices use your frequency band. on
This has nothing to do with whether you use genuine or imitation, large or small wireless microphones. All microphone manufacturers in the world have no way to completely solve the problem of this type of microphone receiver being interfered by other signals of the same frequency. Of course, excellent manufacturers will use technical means to minimize this possibility. The transmitter minimizes spurious emissions such as parasitics, intermodulation, harmonics, etc., while the receiver uses SQ (Squelch, squelch threshold) or narrow Frequency work, frequency hopping technology, etc. In this way, the influence of interference on the system can be solved, and the wireless microphones in the system can be used more frequently.
However, the current relatively effective solution is still to use frequency hopping technology. This technology developed for military-industrial communications was originally a spread-spectrum technology developed for confidential communications after World War II. Now it has been widely used in civil communications, such as CDMA communications.
At present, many manufacturers are trying to apply this frequency hopping technology to wireless microphone systems. This is also a more effective technique to avoid interference. However, due to the high price, it is difficult to popularize.
Most of the interference is formed unintentionally. Generally, it is the interference generated during the normal operation of other equipment. The interference source will not interfere with the transmitter, but the wireless receiver will be interfered. A basic concept should be formed here.
Below, we give a brief description of wireless microphones that are often interfered to let you know where to start under actual conditions. It should be noted that frequency control in mainland China is chaotic and there are many sources of wireless interference:
Because wireless interference involves a lot of knowledge, we use some non-professional terms to describe the whole process here. The purpose is to let users easily master the use of equipment, rather than academic discussion, so friends who are proficient in radio frequency do not need to be too entangled in the text. Terminology and way of explanation.
1. Co-channel interference
2. Electromagnetic interference
3. Intermodulation interference
Co-channel interference:
As the name implies, the frequency you are using has other wireless signals, which hinders the signal propagation of our wireless microphone. This interference enters the machine through the receiver's antenna and makes us unable to receive the wireless microphone signal normally.
It seems to occupy your driving lane. So people who wait for a car are often not waiting for their own car.
1. When walkie-talkies, especially some high-power transmitters, are working, there are a lot of spurious emissions. Maybe the frequency it works is not the frequency we use, but due to out-of-band emissions such as parasitics and harmonics, it should be possible to generate some incidental emissions that fall into our use frequency, causing interference to our wireless microphones.
2. The working frequencies of other wireless transmitting instruments, equipment, microphones, home appliances, and base stations may be the same as the frequencies we use, which interferes with the signal propagation of wireless microphones.
Electromagnetic interference:
Some high-power instruments and equipment will produce high-power harmonic emissions or electromagnetic fields when they work, especially when the distance is very close. These radio frequency energy will be concentrated on some circuits, causing some circuits of the wireless microphone receiver to fail to work.
For example, switching power supplies, induction cookers, microwave ovens, and wireless charging are all energy accumulations in the energy field. The principle of energy destruction is often used in modern warfare. For example, the latest microwave cannons are used to destroy the enemy’s electronic equipment, and high-power directional antennas are often used to interfere with the opponent’s communication equipment. This is the principle.
These devices generate electromagnetic energy accumulation on the surrounding circuits when they work, so there are more signal transmissions that may be interfered with. For example, audio signals, video signals, and wireless signals may all be interfered, and even single-chip microcomputers may be interfered. This is why mobile phone signals and aviation communication signals are not in the same frequency band, and the use of phones and some signal transmission equipment is still not allowed when flying. It might be more straightforward to think about the gas station not allowing mobile phones to be used.
Intermodulation interference:
What is intermodulation interference will not be explained too much. Intermodulation interference is actually a type of co-frequency interference for the receiver. Simply put, the more wireless microphones you use, the more intermodulation interference will be generated. This interference is generated by our wireless microphone itself and comes from the emission of our microphone.
Third-order intermodulation is the most harmful to us. If your two microphones use 800MHZ and 801MHZ respectively, then third-order intermodulation signals will be generated at 799 and 802MHZ frequencies. This signal may affect the use of other microphones. Therefore, the more microphones used, the more interference. However, it should be noted that the intermodulation interference signal strength is lower than the signal strength of the microphone being used.
After talking about these interferences, let's talk about how to avoid them.
Usually when we use wireless microphone equipment, we first plan the installation location of the equipment. The advantage of planning is to avoid electromagnetic interference, so the following principles should be observed during installation;
1. Avoid installing with equipment that may generate strong electromagnetic fields, such as microwave ovens, induction cookers, motors, generators, etc.;
2. Keep away from switching power supply circuits, radio frequency circuits, high-frequency pulse circuits, such as: LED large screens, high-power radios, walkie-talkies, high-voltage generators, negative ion generators, etc. Focus on the large LED screen, because there are a large number of switching power supplies inside, it is easy to affect the work of the receiver;
3. Do not install it in the same cabinet with other equipment, especially equipment with switching power supply and transmitting equipment, such as DVD players, karaoke machines, equipment power transformers, switching power supplies, etc.;
4. When installing wireless microphones, follow the principle of independence and try to stay away from other equipment. Small electromagnetic interference sources are basically separated by more than 50 cm. It is relatively safe. Large interference sources such as LED screens are generally more than 5 meters away.
After the equipment is installed, we need to make a plan for the frequency used by the wireless microphone. The so-called plan is to arrange the frequency we want to use to avoid using the same frequency with other irrelevant signals to avoid receiving interference signals. The easiest way is to turn on all the receivers and wireless microphones we want to use step by step, and then make overall adjustments. Proceed as follows:
Step 1: Turn on all microphones and receivers, and match them well to ensure that each microphone and receiver are connected properly.
Step 2: According to the serial number, turn off the No. 1 microphone and observe the RF (radio frequency signal) indicator of the receiver. This indicator indicates whether there is a signal entering the receiver, and some machine indicators also have an intensity indicator. If the RF signal light is on or there is a change in intensity, it means that a wireless signal of the same frequency enters the receiver. We don't care whether the interference signal comes from the outside world or the intermodulation interference between microphones. We fine-tune the receiving frequency until there is no RF signal.
Step 3: Save the newly selected frequency and match it with the microphone and connect normally. Do not turn off any microphones, they are all on.
Step 4: Turn off the wireless microphone No. 2 and repeat the second and third steps until all the microphones are debugged.
Step 5: Re-check all microphones according to the above steps. If there are still interfering signals, re-adjust the corresponding microphones. Generally, the requirements can be basically met once again.
After the above system debugging, the wireless microphone has basically avoided all the wireless interference signals received from the antenna. In theory, it can be used normally. But we still have to pay attention to the occurrence of a special situation, that is, sudden interference.
(Sudden interference means that during our debugging process, this interference does not exist, but after a period of time, a nearby or surrounding wireless device is turned on, and the frequency used is just the frequency we use. This creates interference with the use of our microphones. This interference is unforeseeable, so we cannot eliminate it in advance work. For example, automatic remote monitoring, monitoring equipment, timing wireless transmission equipment, etc. These equipment may be in trouble In the state of timing or timing transmission, when encountering such interference, it is generally necessary to immediately turn off the microphone receiver and enable the backup microphone.)
For some of the above debugging methods, most of the effects of interference can be avoided. At the same time, many manufacturers have also developed wireless microphone systems that can avoid interference with one button by using the latest technology. All debugging tasks are automatically completed by the action of a button.
Above we have talked about some common interferences and avoidance methods of microphones. Then let's talk about some related issues. These problems are actually common in the use of wireless microphones, but because the domestic performance equipment rental industry does not pay special attention to the radio frequency planning of wireless audio equipment, it has become a weak part of the technology. In this regard, we hope that our domestic counterparts will be integrated with international standards as soon as possible, and the team will be equipped with radio frequency engineers.
1. Sometimes when using, the receiver outputs squeaking sound, sometimes it doesn't.
This interference is frequency interference. The energy is not big, but because it is the same frequency as you use. Therefore, when your microphone signal is weak, the interference signal can have an impact. The characteristics of the wireless signal are strong and suppress the weak, so at this time, it is often a narrow road that meets the brave and wins. Whoever has high power has an advantage.
2. Why the transmission power of the microphone is so small, can't it be made larger?
The conventional wireless microphone is 10-50, the most common is about 30 milliwatts, many of the SHURE-PGX series are 10 milliwatts, and the 10-50 milliwatts of the UR series can be adjusted; Sennheiser's XSW series 10 milliwatts; Sennheiser The EW series is 30 milliwatts; the AMSAUDIO TC series is 30 milliwatts.
The transmission power is different according to the regulations of each country. The same model is set to different transmission power in different countries, and high-power transmission is not conducive to battery life, resulting in shorter use time.
3. Why can the receiver receive some broadcast signals?
There is no essential difference between wireless microphone receivers and ordinary radio walkie-talkies. Most of them use analog carrier frequency transmission. If the broadcast signal falls into the receiving frequency of the receiver, it can be received normally in theory. For example, many open broadcast channels at present happen to be the frequencies that our microphones often use, and it does not rule out the intermodulation signal emission or harmonic emission produced by some broadcast stations.
4. Will rain make the wireless microphone use closer?
Yes, in rainy weather, the rain screen formed by rain has an attenuation effect on the wireless signal, so the working distance of the wireless microphone will obviously become closer.
5. What frequency is good for wireless microphone?
Now mainstream wireless microphones all use U-segment work, around 500MHz-850MHz. Some major brands have produced G-segment (1000MHz-2400MHz) microphones, and most domestic manufacturers produce microphones around 700MHz-850MHz. The V-segment machine is a product of the previous generation, and it is rarely used as a show now.
What frequency microphone is good to choose, we must first talk about the high and low frequencies in the microphone. There is a characteristic of radio frequency work. The higher the frequency, the more it tends to be light. The lower it is, the more it tends to be the characteristics of the sound. The high frequency direct radiation is good, the linear transmission, the frequency bandwidth occupies relatively little. If it is low, the diffraction is good, and it is easy to go around. This also explains why the long-distance communication uses shortwave.
High frequencies are used at short distances, and low frequencies are used at long distances. So when our microphone uses a higher frequency, it is very susceptible to any slight environmental changes, even if you wave your hand, it may cause a short loss of signal.
Therefore, the distance is a big problem if it is transmitted at a higher frequency. We can refer to Senhai’s latest 2.4GHz products. He recommends you to use the lecture class of the conference church and does not recommend you to do performances.
When working in a lower frequency band, it is more susceptible to interference, because the current low frequency wireless environment is very complicated and there are many interference sources, so the low frequency band is more dangerous.
But the above points are not the basis for your choice of microphone frequency, because the above reasons are real, but in actual use, it is in the current 500MHz-850MHz frequency band. The effect of high and low on the user is not particularly obvious. The frequency selection mainly depends on the frequency bands of the current microphones and the frequency bands of the open-circuit broadcasting in the current city. For the above frequency bands. Choose the frequency to avoid repetition as much as possible.
6. Why is the frequency of the wireless microphone cut off, and how to distinguish the phenomenon?
Frequency cut is a problem often encountered in the work of wireless microphones. Simply put, the phenomenon after the wireless microphone loses connection with the receiver is called frequency cut.
Frequency cutout is a comprehensive phenomenon. Any problems with wireless microphones and receivers may cause frequency cutoffs. Therefore, it cannot be said that the frequency cutoffs must be caused by interference.
Interference cuts off the frequency, the receiver receives interference, causing it to be unable to receive the microphone signal normally, so the cut off can generally be judged by turning off the wireless microphone and checking the receiver's RF signal indication. If there is interference, the signal indicator will light up.
The frequency is cut off in the distance, and the wireless microphone exceeds the range of the receiver to receive the signal, resulting in frequency cut off. This kind of frequency interruption can be eliminated by controlling the range of use of the wireless microphone.
Installation error frequency cutoff, this kind of frequency cutoff is often in actual use, the use distance is significantly smaller than the conventional use distance. It is common to use the wrong installation cabinet or install the equipment in the wrong place. Pay attention that the antenna of the receiver should be completely exposed, and the two antennas should be at a V-shaped angle. Try to avoid obstacles between the entire receiver antenna and the crowd and the microphone.
7. It's good during rehearsal. The microphone will interfere or cut off during the formal performance.
First of all, it is necessary to distinguish which type of fault belongs to. Generally, during rehearsal, the wireless microphone is turned on and tried, and then the performance is officially performed. Various problems are found after using the wireless microphone for a while. These problems often make people confused and at a loss because they cannot be debugged twice in the field.
----------- There are creaking noises from many wireless microphones, and even some microphones have no sound at all. Sometimes it is not even clear which microphone has the noise.
This situation is generally caused by the intermodulation interference of the microphones. Because there is no overall adjustment, after the official performance, as the order of the microphones is disrupted, and the number of microphones increases or changes, the intermodulation interference of the microphones appears, causing some microphones to fail. Work, this situation is difficult to rule out temporarily. Generally, some microphones are turned off and do not use them.
Therefore, the microphones should be tuned before the performance. In this case, the closer the receiver is to the stage, the more obvious it is, especially on the side of the stage or when an antenna amplifier is used.
(It is correct that the receiver is close to the stage, but when the system is not tuned, the intermodulation interference signal is more likely to enter the receiver because it is close to the receiver)
-----------Wireless
There is noise or no signal in one of the tubes.
This situation may be that this set of microphones is subject to sudden interference from the same frequency. Generally, it is only necessary to turn off the microphone and then adjust the receiver frequency. Observe the signal, avoid interference, and re-match the microphone, but this set of re-matched microphones is recommended as a backup microphone, because it is very likely to form intermodulation interference with other microphones that were tuned first.
----------The distance of the wireless microphone is getting closer, even the frequency drop is serious, and many sets of microphones are like this.
This situation often occurs when the receiver is on the opposite side of the stage, leaving a large audience area in the middle. It rarely happens when the receiver is on the side of the stage.
Because there is no audience between the microphone and the receiver during the rehearsal, the signal transmission is relatively normal. At formal events, a large number of people gather between the microphone and the receiver, and 70% of the people are water. Water has a serious blocking effect on the propagation of wireless signals, especially U-segment wireless signals, so the distance becomes closer and the frequency drops easily.
The correct method is to place the receiver near the stage, or place the receiver higher than the crowd. If necessary, you can use an antenna distribution system to improve the reception of wireless signals.
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