The performance of the wireless microphone is often affected by various factors such as the frequency interference of the surrounding equipment, improper operation of the user, etc., and various failures occur. Next, the editor will teach you how to avoid and prevent the most common wireless microphones problem.
01 Insufficient compatibility of the entire system
There are different degrees of compatibility between frequencies. If you know the system conditions well, you can boldly adopt more systems, but the key is how to weigh the compatibility of the entire system.
Most frequency compatible software has an important assumption when designing, that is, all receivers are always on or unmute (even if some transmitters are occasionally turned off), so as to ensure that all receivers will not pick up To intermodulation signals that may generate noise.
In this case, it is assumed that the operator will mute all receivers and all transmitters will remain during the performance. The distance between the transmitter and the receiving antenna is also the same. These assumptions are completely feasible in Broadway theater performances, but in the school auditorium, the system is operated by personnel without professional training, and it is not great to achieve the same expected performance. It's possible.
When the location of the transmitter is very close to the receiving antenna, or the high-power transmitter is running, the interference phenomenon will be more serious. This is why it is far more difficult to have 40 wireless systems working at the same time in a movie theater than in school (many transmitters are very close to the receiver). Each classroom in the school has a system, and the transmitters are completely Independent, but each close to its own receiver.
Solution: A balance between a larger number of system devices and high performance should be achieved, and the compatibility level between frequencies should be ensured to be suitable for the expected use of the system. Keep a distance of at least 10 feet between the transmitter and the receiving antenna. If the RF output power of the transmitter is adjustable, use a lower transmission power to cover the expected distance between the transmitter and the receiver.
02 The system itself is not compatible
When using wireless microphones, there are always interference problems between the systems themselves. Although the frequency or interval of each system is several megahertz, intermodulation distortion (IMD) still causes the phenomenon of mutual interference between microphones. If there is not enough megahertz space between the intermodulation signal and the operating frequency of the device, it is difficult for the receiver to pick up the signal from the transmitter.
Typical phenomena are crosstalk between systems, frequent signal loss or excessive noise and distortion. The small separation between frequencies depends on the design of the system receiver, and entry-level receivers may require a 1MHz separation from the nearest adjacent system. The more expensive receivers usually have a narrower adjustment "window", allowing a smaller intermodulation frequency interval between each system.
Solution: In order to avoid intermodulation distortion, select a compatible frequency that has been calculated. This requires a wealth of transmitter and receiver design knowledge, and wireless system manufacturers often have already calculated these frequencies. For example, when only 8 wireless microphones are used together, thousands of calculations must be performed to ensure compatibility between the microphones.
03 Interference from other signal sources such as TV stations
Wireless microphones are also subject to interference from other signal sources transmitted in the same frequency spectrum. The most common ones are usually TV stations. For example, FCC regulations require users of wireless microphones to avoid using frequencies occupied by broadcast TV stations in the same geographic area.
Solution: Indoors, avoid interference from 40-50 miles of TV channels. When working outdoors, it should be used normally within a radius of 50-60 miles. Since the frequency of each city is different, the suitable frequency of the wireless microphone depends on the place where it is located.
04 Interference problems with other digital devices
Other wireless audio devices such as ear monitors, intercom systems, and non-wireless devices can also cause interference problems. If digital devices (CD players, computers, and digital audio processors) are installed close to the wireless microphone receiver, they often emit strong radio frequency noise and may cause interference. For transmitters, the most common sources of interference are GSM mobile phones and PDAs worn by the host.
Solution: When selecting the wireless microphone frequency, you must clearly understand other wireless audio devices. Keep at least a few feet between the digital device and the wireless microphone receiver.
05Receiving antenna selection and layout
The receiving antenna of the wireless microphone is one of the most misunderstood areas. Antenna selection, layout, and wiring errors can all lead to short performance coverage areas and low signal strength, resulting in frequent disconnections. The performance of modern diversity receivers is far superior to that of a single antenna type, but to optimize system performance and reliability, antenna selection and layout must be correct.
To ensure a good diversity performance of the system, at least one half-wavelength (approximately 9 inches 700MHz) in the antenna space is guaranteed. The angle of the receiving antenna should be a "V" configuration, which can provide better signal pickup performance when the transmitter is moved or placed at different angles.
If the receiver is installed far away from the performance area (such as in the equipment closet or enclosed rack), a half-wave antenna or directional antenna (preferably above the audience) should be installed remotely, so that there is a clear view between the transmitters. Boundary line of sight. Do not install ¼ shortwave antennas remotely because they use the receiver case as a ground antenna. If the antenna is installed far away from the stage, you can use a directional antenna to improve signal reception by picking up more signals in this direction and reducing signal pickup from other angles. If a coaxial cable is used to connect the antenna to the receiver, it may be necessary to use an antenna amplifier to solve the problem of signal loss in cable transmission.
The loss of the signal quantity depends on the specific length of the cable and the cable type. Therefore, please calculate according to the manufacturer's recommendation. The total net loss of the signal should be controlled within 5dB.
06 Man-made wireless signals are blocked
The human body may also interfere with wireless signals. The human body is mainly composed of a large amount of water and can absorb radio frequency energy. In addition, if the user wraps his hand around the external antenna of the handheld transmitter, its effective output can be reduced by more than 50%. Similarly, if the flexible antenna on the transmitter is curled or folded, the signal will also be affected.
Solution: Keep the transmitter antenna fully expanded and unblocked to achieve a larger range of signal transmission to achieve better performance.
07 The battery voltage of the transmitter is not enough
The battery life of the transmitter is the primary concern of wireless microphones, and users always try to reduce the cost of the device through low-cost batteries. Most wireless manufacturers specify alkaline batteries or disposable lithium batteries because their output voltage is relatively stable throughout the battery life cycle.
This is very important, because most transmitters will experience acoustic signal distortion or signal loss under low voltage conditions. Rechargeable batteries often seem to be the ideal solution, but most rechargeable batteries, even if they are fully charged, provide a voltage that is 20% lower than that of disposable batteries.
Solution: In order to solve the battery problem, carefully compare the voltage output requirements of the transmitter battery at any time to ensure the sustainability of the battery during the entire working process.
08 non-adjustable transmitter
The inherent noise and limited dynamic range of FM transmission make analog wireless audio transmission have its limitations. To overcome this, most wireless microphone systems usually use two audio processing methods to improve sound quality. Add pre-emphasis equipment to the transmitter and de-emphasis equipment to the receiver to improve the signal-to-noise ratio of the signal. The compressor and receiver extender in the transmitter can increase the dynamic range by more than 100dB. This makes the volume setting very important. If the audio level is too low, it will produce a hissing sound; if it is too high, it may cause distortion.
Solution: To obtain better sound quality, the input gain of the transmitter should be adjusted so that full modulation occurs when a higher volume is produced, but without distortion.
09 wireless system settings
The most troublesome problem with wireless systems is that the waves themselves are constantly changing. Since the transition to digital TV, the waves of analog and digital TV channels have continued to change.
Solution: It used to be easy to know whether the VHF band TV channel of the city where the user is located is odd or even. However, now when people install and use wireless microphones (and in-ear monitors and intercom systems, etc.), they must regularly check the local spectrum conditions even when working in a venue they are familiar with.