The performance of wireless microphones is often affected by various factors such as frequency interference, user error operations, etc., and various failures occur. This article will teach you how to avoid and prevent the most common wireless microphone problems.
1: 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. Therefore, most manufacturers have published a list of frequencies compatible with their systems. In addition, software can also be used to help users identify compatible frequencies in some cases.
2: 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.
Therefore, the software needs to leave enough space for intermodulation signals and wireless microphones when designing. If you assume that the sound system operator will play a more active role in the activity, then you need the system to have a wider range of compatibility. 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.
3: 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. FCC rules 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. Equipment manufacturers usually provide guidelines to inform users of the different frequency of use in different cities.
The FCC required all analog TV stations to cease operations in February 2009. At the same time, the frequency spectrum above channel 51 will be used for other purposes. The frequency of the wireless microphone above 698MHz should be adjusted to a lower frequency to avoid interference with new services. As the conversion continues, the TV channel in a particular location may change, so users are better to check official profile information regularly.
4: Interference problem of other digital equipment
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.
5: Selection and layout of receiving antenna
The receiving antenna of the wireless microphone is one of the larger areas that is misunderstood. Antenna selection, layout, and wiring errors can all lead to short distances in 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.
Solution: To ensure good diversity performance of the system, at least one half-wavelength (approximately 9 inches 700MHz) of the antenna space should be 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. The extra distance between the antennas will not significantly improve the diversity performance of the system, but it may better cover a larger area of the stage, church or conference room. 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.
6: Man-made wireless signal is 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.
7: 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. Lithium-ion batteries and rechargeable alkaline batteries usually can work continuously, while nickel-metal hydride and nickel-cadmium batteries may only last a few hours. This is especially true for 9-volt batteries, AA rechargeable batteries have similar performance to disposable AA batteries.
8: 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, a hissing sound will be produced; 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.
9: The receiver output level is set incorrectly
With so much discussion on frequency, wavelength and antenna, it is easy to overlook the most basic requirements of a wireless microphone system: In order to replace the connection cable between the signal source and the audio system, the receiver is usually equipped with output level control, and Most wired microphones do not. This provides a better opportunity for finer matching between the output of the receiver and the input.
Solution: Regardless of the microphone level or the line level, the output level should be set to a practicable higher level, while not exceeding the limit of the audio system input, which may be indicated on the input channel of the mixer , Can also be judged by listening to the sound distortion.
10: 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. The FCC is trying to find a way to make consumer products (personal PDAs, smart phones or home devices) use vacant TV channels for wireless Internet access.
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.
Of course, this is far less complicated than we thought. First of all, most wireless equipment manufacturers can now provide online frequency selection tools to synchronize updates with newer TV channels. Secondly, both external RF scanners and spectrum analyzers can quickly scan the entire spectrum (including TV bands), and are becoming more powerful and cheaper, providing a more practical choice for those who rely heavily on wireless systems. . Finally, the wireless system itself has gradually become more complex. Even some entry-level systems can scan the spectrum or find an open spectrum. Some high-quality systems can even be connected to your PC or Mac, scan the spectrum, give you an intuitive RF status description, and calculate a set of better frequencies (considering other RF equipment), and then automatically set the reception Device.