With the popularity of wireless microphones, it has brought great convenience to users, and at the same time, more or less problems have arisen. One of the problems often encountered is the instability caused by the conflict between the frequency of the wireless microphone system itself and the external frequency, and the insecurity caused. Therefore, it is necessary to use limited frequency resources between intensive conference rooms to plan the use of the frequency of the wireless microphone system to ensure smooth and safe meetings. Let's take the sound reinforcement system of an auditorium as an example to explain the specific solutions when the wireless microphone system encounters frequency interference, and how to do spectrum management.
1 Distribution of spectrum resources
The basic working principle of the wireless microphone system is very simple, that is, the sound signal is converted into an electrical signal, and then modulated by FM (frequency modulation) onto a carrier and transmitted by the transmitter, and then received and demodulated by the receiver into an audio signal, and sent to the amplifier. In the sound system. Therefore, the wireless microphone system is a one-way communication system, which is different from the walkie-talkie system. According to the revised "Technical Requirements for Micropower (Short Range) Radio Equipment" issued by the Radio Technology Management Committee of the Ministry of Information Industry of China in September 2005, devices such as wireless microphones and civil radio meters use 470 MHz to 510 MHz, 630. MHz to 787 MHz band; transmit power limit: 50 mW (erp); occupied bandwidth: no more than 200 kHz. Universal wireless remote control devices use 470 MHz to 566 MHz, 614 MHz to 787 MHz, which are the range of use of wireless devices.
However, it should be noted that the actual use of these bands should avoid the frequencies used by local radio stations and TV stations. Most of the frequency bands of imported wireless microphone systems are above 450 MHz, especially from 470 MHz to 787 MHz. The following is an analysis of the frequency interference problem encountered in an actual use of an imported brand wireless microphone system used in the sound reinforcement system. The wireless microphone system uses a portion of the UHF IF band, while the UHF range is 470 MHz to 806 MHz, which can accommodate more operating frequencies. The receiver of the system uses two 1/2 wavelength diversity antennas. This diversity receiving technique can effectively eliminate "dead spots" and "dead spots" and avoid broken or sub-tones. Therefore, the key issues to be solved are spectrum resource management and external frequency interference.
2 Measures to avoid frequency interference
(1) Find out the frequency of the wireless microphone system used by the sound reinforcement system
The data of the frequency points currently used by the wireless microphone system of several adjacent rooms are collected, statistically sorted, and analyzed.
(2) Confirm external interference sources and available frequency points
The frequency sweep monitoring is performed by using the management software adapted by the wireless microphone system. The software assists in the identification of RF signals and searches for interference-free operating spectrum. According to the national standard GB/T 14431-1993 "Signal/interference protection ratio and minimum available field strength required by the radio service", find out the strong interference frequency exceeding the interference protection ratio, and discard it, find out that The frequency of interference but still usable. Measure the isolation of the wireless microphone signal between the auditorium and adjacent rooms. If the isolation of some frequency points is very high, more than 40 dB, that is to say, the attenuation of the signal of these frequency wireless microphone signals is greater than the interference protection ratio, these high isolation frequency points can also be used simultaneously in each conference room or hall. .
(3) Strict frequency configuration
According to the previous work, confirm the interference frequency and the available frequency. In the available frequency range, configure the frequency used by the wireless microphone according to the same frequency configuration, adjacent frequency configuration and in-band configuration greater than 50 kHz. All available frequency points are tabulated and assigned to each meeting room or room. At the same time, a part of the frequency of the adjacent frequency configuration is reserved for use by journalists and other outsiders.
(4) Establishing a spectrum management system for wireless microphones according to frequency configuration
This core work, whether it is the current wireless microphone system or adding a new wireless microphone system in the future, needs to pay attention to the internal intermodulation between the frequencies, especially the third-order intermodulation, which needs to check the frequency of the relevant brand wireless microphone manufacturers. The table makes the spectrum used by all systems orderly, rather than setting a frequency to work. In this way, the mutual interference of the wireless microphone signals between the auditorium rooms is avoided first; on the other hand, the journalists need to use the wireless microphone, must apply, and then allocate a frequency of the adjacent frequency configuration, no matter which room they interview, Neither will it interfere with the wireless microphone being used. Another issue to be aware of is that each system should be set aside with several backup frequencies in case of manual replacement in case of an emergency. In short, these spectrum resources are allocated and used more rationally through specification management.
(5) Make full use of the convenience brought by the management software of the wireless system
Using software to find the advantages of frequency points can greatly improve work efficiency, and can monitor the working state of the system and the status of each antenna signal at any time. In recent years, the brand used in this system has a new wireless microphone system that integrates interference detection and avoidance, frequency diversity, remote control, power management, software control, frequency backup and automatic conversion. If you can upgrade to this system, it will bring more convenience to daily use and have a more stable system.
(6) Strengthen the monitoring of the venue environment
Since external interference sources change at any time, it is necessary to strengthen the monitoring of the venue environment. The wireless system management software is often used to scan and collect on-site RF data, record occasional or sudden RF interference, and find out the source of interference. Pay attention to the RF RF indicator on the receiver panel during daily work to see if there are other signal interferences. If so, continue to look for sources of interference.
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