What are the wireless interference sources?

There are many types of wireless interference sources.

1. Co-channel interference 2. Electromagnetic interference 3. Intermodulation interference

Co-channel interference

As the name implies, the frequencies we use have other wireless signals, which hinders the signal propagation of the wireless microphone. This interference enters the machine through the antenna of the receiver, so that we cannot receive the signal of the wireless microphone normally.

1. When the walkie-talkie, especially some high-power transmitters, work, the spurious emissions are particularly large. Perhaps the frequency at which it works is not the frequency we use, but due to out-of-band emissions such as parasitic, harmonics, etc., it should be possible to generate some incidental emissions that fall into our frequency of use, causing interference to the wireless microphone.

2. The operating frequency of other wireless transmitting instruments, equipment, microphones, home appliances, and base stations may be the same as the frequency we use, which causes the wireless microphone signal to be interfered with.

Electromagnetic interference

Some high-powered instruments produce high-power harmonic emissions or electromagnetic fields during operation, especially at very close distances. These radio frequency energy is concentrated on some circuits, causing some of the circuits of the wireless microphone receiver to be inoperable.

For example, switching power supplies, induction cookers, microwave ovens, and wireless charging all belong to the energy field. In modern warfare, the principle of energy destruction is often used, such as the latest microwave guns, which are used to destroy enemy electronic equipment, and communication equipment that often uses high-power directional antennas to interfere with each other.

These devices operate with electromagnetic energy accumulation on the surrounding circuits, so there may be more signal transmissions that may be disturbed. For example, audio signals, video signals, and wireless signals may be subject to interference, and even the microcontroller can be interfered.

Intermodulation interference

Intermodulation interference is actually a type of co-channel interference for the receiver. Simply put, the more wireless microphones used, the more intermodulation interference is generated. This interference is generated by the wireless microphone itself and is derived from the microphone's transmission.

The third-order intermodulation is the most damaging. If you use 800MHZ and 801MHZ for the two microphones, then the third-order intermodulation signal will be generated at 799 and 802MHZ. This signal may affect the use of other microphones, so the microphone The more you use, the more interference you have. However, it should be noted that the intermodulation interference signal strength is lower than the microphone signal strength being used.

How to avoid?

Usually when using a wireless microphone device, first plan the installation location of the device. The planned benefit is to avoid electromagnetic interference, so the following principles should be observed during installation:

1. Avoid installation with equipment that may generate strong electromagnetic fields, such as microwave ovens, induction cookers, electric motors, generators, etc.

2, try to stay away from the switching power supply circuit, RF circuit, high-frequency pulse circuit, such as: LED large screen, high-power radio, walkie-talkie, high-voltage generator, negative ion generator. Focus on the LED large 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, such as DVD player, karaoke machine, power transformer of equipment, switching power supply, etc.

4. When installing the wireless microphone, follow the independent principle and try to stay away from other equipment. The small electromagnetic interference source is relatively safer than 50 cm apart. If the large interference source is like the LED screen, it is generally safer than 5 meters.

After the equipment is installed, it is necessary to plan the frequency used by the wireless microphone. The so-called planning is to arrange the frequency to be used to avoid using the same frequency with other unrelated signals to avoid receiving interference signals. The easiest way to do this is to step through all the receivers and wireless microphones you want to use and then tune them. Proceed as follows:

Step 1: Turn on all the microphones and receivers and match them to ensure that each microphone and receiver work properly.

Step 2: According to the 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 to enter the receiver. Some machine indicators also have an indication of strength. If the RF signal light is on or there is a change in intensity, the wireless signal with the same frequency enters the receiver. Do not care whether this interference signal originates from the outside or the intermodulation interference between the microphones. Fine-tune the receive frequency until the RF signal is not available.

Step 3: Save the newly selected frequency and match the connection with the microphone. Do not turn off any microphones, all are turned on.

Step 4: Turn off the No. 2 wireless microphone and repeat the second step and the third step until all the microphones have been debugged.

Step 5: Follow the above steps to check all the microphones again. If you find that there are still interference signals, debug the corresponding microphones again. Generally, the basic requirements can be met.

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 a special situation, that is, sudden interference.

(Sudden interference means that during the 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, so This interferes with the use of the microphone. This interference is unpredictable and therefore cannot be eliminated in advance work, such as automatic remote monitoring, monitoring equipment, timed wireless transmitting equipment, etc. These devices may be in an irregular or timed transmission. State, 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 them can avoid the influence of interference. At the same time, many manufacturers have also developed a wireless microphone system that can avoid interference by one button using the latest technology, and automatically complete all debugging work by one button action.

Analysis of common problems in wireless systems

The above mentioned some common interference and avoidance methods of the microphone. Then let's talk about some related issues.

1. Sometimes when the receiver is used, the receiver outputs a squeaky sound, sometimes not.

This interference is frequency interference. The energy is not big, but it is the same frequency as you use. Therefore, when your microphone signal is weak, the interference signal can be affected. The characteristics of the wireless signal are strong and weak, so this time is often the narrow road to meet the brave. Whoever has the power, who has the advantage.

2. Why is the transmission power of the microphone so small, can't it be bigger?

Wireless microphones are routinely 10-50, the most common being around 30 milliwatts.

The transmit power varies according to the regulations of each country. The same model is set to different transmit powers in different countries, and high-power transmission is not conducive to the battery life, resulting in shorter use time.

3. Why can the receiver receive some broadcast signals?

There is no essential difference between the wireless microphone receiver and the ordinary radio transceiver. Most of them use analog carrier transmission. If the broadcast signal falls into the receiver's receiving frequency, it can theoretically be received normally. For example, many broadcast open channels are just the frequencies that our microphones often use, and we do not rule out the intermodulation signal transmission or harmonic emission generated by some broadcast stations.

4. Will it make the wireless microphone use a closer distance when it rains?

Yes, rainy days, because the rain screen formed by the rain has attenuating the wireless signal, the use distance of the wireless microphone will obviously become close.

5. What frequency is good for wireless microphones?

Now mainstream wireless microphones use U-segment work, around 500MHz-850MHz. Some brands have already produced G-segment (1000MHz-2400MHz) microphones. The V-segment machines are the products of the previous generation and are rarely used as performances.

To choose which frequency of the microphone is good, you must first talk about the high and low frequencies in the microphone. There is a characteristic of RF operation. The higher the frequency, the more it tends to be light. The lower the level, the more it tends to sound. High-frequency directivity is good, linear transmission, frequency bandwidth occupation is relatively small. Low, the diffraction is good, easy to wrap around, which also explains why short-distance communication uses shortwave.

High frequencies are used at close range and low frequencies are used at long distances. So when our microphones use higher frequencies, they are easily affected by any little environmental changes, even if you wave, it may cause a short loss of signal.

When working in the lower frequency band, it is more susceptible to interference. Because the wireless environment in the low frequency band is very complicated and there are many interference sources, the low frequency band is dangerous.

However, the above points are not the basis for your choice of microphone frequency, because the above reasons are true, but in actual use, in the current 500MHz-850MHz frequency band. The effects of high and low on the user are not particularly obvious. The frequency selection mainly depends on which frequency bands are currently available to the microphones in the current city. For the above frequency bands. Choose to avoid repetitions as much as possible.

6. Why does the wireless microphone break the frequency, how to distinguish the phenomenon?

Frequency-breaking is a problem often encountered in the work of wireless microphones. Simply speaking, the phenomenon that the wireless microphone and the receiver lose connection is called frequency-breaking.

The frequency-breaking phenomenon is a comprehensive representation, and any problem with the wireless microphone and the receiver may cause a frequency cut, so it cannot be said that the frequency cutoff must be caused by interference.

The interference is cut off, and the receiver receives the interference, which makes it impossible to receive the microphone signal normally. Therefore, the frequency cut can be judged by turning off the wireless microphone to check the receiver's RF signal indication. If there is interference, the signal indicator lights up.

The distance is cut off, and the wireless microphone exceeds the range of the receiver's received signal, causing a frequency cut. This frequency cut can be eliminated by controlling the range of wireless microphone use.

The installation error frequency is broken. This kind of frequency cut is often used in actual use, and the use distance is obviously smaller than the conventional use distance. It is common to use the wrong installation cabinet, or install the equipment in the wrong place. It should be noted that the antenna of the receiver should be completely exposed, and the two antennas are V-shaped. The entire receiver antenna should be avoided as much as possible between the crowd and the microphone.

7, the rehearsal is good, the microphone will have interference or frequency cut during the official performance.

First of all, it is necessary to distinguish which type of fault belongs to. In general rehearsal, the wireless microphone is turned on and tried, and then the performance is performed. The wireless microphone will find various problems after using it for a while. These problems are often unpredictable because they cannot be debugged twice in the field.

8, many wireless microphones appear squeaky noise, and even some microphones have no sound at all, and sometimes it is not clear which microphone has noise.

This situation is generally caused by the intermodulation interference of the microphone. Since there is no overall adjustment, after the official performance, as the microphone sequence is disordered, and the number is increased or changed, the intermodulation interference problem of the microphone appears, resulting in some microphones not being able to Work, this situation is difficult to rule out temporarily. Generally turn off some microphones, don't use them.

Therefore, the microphone should be adjusted 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.

(The receiver is close to the stage, but when the system is not tuned, the intermodulation interference signal is easier to enter the receiver because it is closer to the receiver.)

9. The wireless microphone has only one noise or no signal.

In this case, the microphone may be subject to sudden interference at the same frequency. Generally, it is only necessary to turn off the microphone and then adjust the receiver frequency. Observing the signal, avoiding the interference, and re-matching the microphone is fine, but this set of re-matched microphones is recommended as a backup microphone because it is highly likely to form intermodulation interference with the other microphones that were originally tuned.

10, the wireless microphone distance is getting closer, even the frequency is serious, and many sets of microphones are like this.

This happens a lot when the receiver is on the opposite side of the stage, with a large audience area in the middle. Generally, the receiver rarely occurs on the side of the stage.

Because there is no audience between the microphone and the receiver during rehearsal, the signal transmission is relatively normal. During formal events, a large number of people gather between the microphone and the receiver, and 70% of the people are water. Water plays a serious role in blocking wireless signal propagation, especially the U-band wireless signal, so the distance becomes close and easy to drop frequency.

The correct way is to place the receiver near the stage, or place the receiver above the crowd, and if necessary, use an antenna distribution system to improve the reception of wireless signals.