The root causes of crosstalk of multiple wireless microphones in KTV box and a complete set of radical solutions

Many KTV operators and Andhadhun will encounter the same headache: when four or six wireless microphones are turned on in the box at the same time to sing, there will be microphone sounds jumping around, microphone A talking and microphone B making noise, noise cutting off, frequent howling, and even the microphones in the next box interfere with each other. Most people will simply change the channel to cope with the temporary situation, and treat the symptoms rather than the root cause. This paper dismantles the core source of cross-frequency, with a complete solution from procurement, pre-commissioning to on-site emergency.
First, the three core sources of multi-wheat series frequency in the same box
(1) Intermodulation interference in the same frequency band/adjacent frequency points (the most common internal cause)
Receiver channel frequency interval is insufficient.
Low-cost wireless microphones with one pull for four and one pull for eight, with internal frequency channel spacing less than 200KHz and industry standard professional equipment spacing ≥500KHz. When multiple microphones transmit signals at the same time, radio waves with different frequencies produce intermodulation products in the internal circuit of the receiver, resulting in overlapping clutter, crosstalk and wheat channeling.
Frequency points get together continuously.
When tuning, randomly select consecutive adjacent channels, such as CH01, CH02, CH03, and CH04, where RF signals squeeze each other, and weak signal microphones are directly covered by strong signals, which shows that the main microphone sound escapes to other microphone channels.
(B) the equipment hardware grade is insufficient and the RF isolation is poor.
Low-cost all-in-one shared RF motherboard
Low-cost multi-microphones, multi-channels share a RF receiving board, the shielding and filtering circuits between channels shrink, and the channel isolation is extremely poor. The signal transmitted by one microphone will be concatenated into other receiving channels, which is the hardest hit area for small KTV crosstalk.
Lack of antenna distribution system
Multiple receivers are stacked and share a simple antenna, and the signals reflect and overlap with each other, and the RF signals of different microphones are mixed at the antenna end, which directly causes cross-channel crosstalk.
(3) Environmental and external external RF interference (the main cause of cross-box cross-frequency)
Box wall without RF shielding
Ordinary light steel keel+gypsum board wall can't isolate UHF wireless signal, and the microphone signal of this box penetrates the wall and enters the receiver of the next box, resulting in cross-talk between rooms.
External clutter superposition interference
Box routers, jukeboxes, Bluetooth devices, large LED screens, and switching power supplies will all release 2.4G RF clutter, which will interfere with UHF wireless microphone reception. A large number of microphones in the whole balcony work at the same time, and the radio frequency spectrum in the air is crowded, so the frequency points are easy to overlap and crosstalk.
Unreasonable antenna placement
When the receivers are all stuffed into the deep part of the cabinet, the antennas are intertwined, and the antennas are close to the metal cabinet, the metal will reflect the RF signal, resulting in signal reflection superposition and induced crosstalk noise.

Second, the layered solution of multi-wheat series frequency in the box (from emergency temporary plan to long-term radical plan)
(A) On-site rapid emergency: a debugging method that can be operated immediately.
Suitable for boxes that are open and cannot be replaced with equipment, and quickly relieve cross-frequency.
Frequency spectrum scanning, interval frequency hopping channel selection
Turn on the automatic frequency scanning function of each receiver to avoid the frequency points in the interference red zone marked on the screen; The frequency points of multiple microphones must be separated, and four microphones should be separated by at least three channels, for example, CH05, CH09, CH13 and CH17, so as to prevent continuous frequency points.
Put antennas separately, away from metal interference.
Each receiver is independently equipped with an antenna, and all the antennas are pulled out and hung on the wall outside the cabinet. Do not entangle or cling to the metal cabinet, power amplifier and wire. The receiver antennas of the upper and lower cabinets are staggered to avoid signal reflection.
Turn off idle microphones to reduce the radio frequency load in the air.
Turn off all microphones that don't sing, and don't stand idle for standby. The fewer RF signals are transmitted simultaneously in the air, the lower the probability of intermodulation interference, and the crosstalk and noise are greatly reduced.
Reduce the transmitter power of microphone
Turn down the transmitting power in the menu of the receiver (divided into three grades: high/medium/low). If the box space is not large, just choose the mid-range power, so as to reduce the probability of RF signal overflowing through walls and channels.
(B) Mid-term optimization: low-cost transformation, greatly reducing cross-frequency.
Install antenna distributor+passive antenna amplifier.
More than four or more multi-wheat boxes must be matched. An antenna distributor can share independent pure antenna signals for multiple receivers, and the RF signals between devices are physically isolated, thus solving the problem of mutual crosstalk of multiple receivers sharing antennas; Large-area long box is equipped with antenna amplifier to enhance pure main signal and suppress clutter and crosstalk.
Modification of cabinet line specification
The RF antenna signal line is routed separately and not bundled with the power line and audio signal line; Metal shielding partitions are installed inside the cabinet to separate each receiver and improve the channel isolation.
Distinguish floor/box frequency band groups
The planned frequency points of the whole floor KTV partition: 1-5 boxes use a frequency point, 6-10 boxes use a frequency point, and the two frequency bands are completely non-overlapping, so as to prevent cross-box wheat string from the root.
(C) Long-term radical cure: hardware procurement standards, completely eliminate cross-frequency.
Reject the cheap integrated multi-microphone and choose an independent dual-channel receiver.
Priority is given to 2-channel independent receiving host, one machine for every 2 microphones, and the internal RF circuit is shielded independently, with channel isolation ≥80dB, and there is almost no cross-talk in the channel; Avoid a single motherboard and integrate a low-cost model.
Look for standard UHF broadband equipment, with channel spacing ≥500KHz.
Confirm the equipment parameters when purchasing: the frequency channel interval is 500KHz or above, which supports intermodulation suppression technology. The equipment has its own intermodulation interference elimination chip, and multiple signals work at the same time without generating clutter intermodulation products.
Large area box with directional antenna
For large boxes and duplex boxes over 40㎡, the omnidirectional antenna should be abandoned, and the directional flat antenna should be used to control the RF signal within the box range, so as to reduce the signal leakage through the wall and prevent the crosstalk in the box next door.
Reasonable zoning and matching of shielding materials
When the wall is rebuilt, a metal radio frequency shielding net is added in the light steel keel of the audio-visual room; All-metal shielded professional audio cabinet is selected to block RF reflection crosstalk.

Third, the daily operation and maintenance of long-term anti-crosstalk operation specifications
Daily pre-business spectrum inspection
Turn on the receiver to scan the spectrum before the opening ceremony. Every day, the surrounding merchants and new electronic equipment will change the ambient radio frequency, and replace the occupied interference frequency points in time. Don't fix a group of channels all the year round.
Microphone grouping fixed management
The number of microphone and receiver in each box is bound, and the microphone transmitter is not changed randomly across boxes; Microphones in boxes with different frequency bands are stored separately to avoid frequency point conflict caused by mistake.
Regular equipment maintenance and cleaning
The signal distortion will be caused by the oxidation of the antenna interface of the receiver and the aging of the wire. Check the antenna connector every month; If the battery voltage of microphone transmitter is insufficient, the RF signal will be disordered. If the battery is low, replace it in time, and low-voltage clutter is also the hidden cause of crosstalk.
Wiring to avoid radio frequency pollution sources
The router, the song ordering host and the LED controller are at least 1.5m away from the receiver cabinet, and the power adapter is far away from the RF antenna, so as to reduce the interference of pulse clutter on the wireless receiving spectrum.
Fourth, the correction of common misunderstandings
Myth: If the frequency number is different, there will be no cross-frequency.
Correction: adjacent frequency points will produce intermodulation interference. Even if the numbers are different, continuous adjacent channels will still skip, and sufficient channel spacing must be skipped.
Myth: The greater the power, the more stable the signal.
Correction: High power will make RF signals pass through walls and overflow channels, which will aggravate cross-box and channel cross-frequency. Small boxes do not need to transmit at full power.
Myth: it's easier for many wheat to share an antenna.
Correction: sharing antenna is the number one inducement of multi-channel serial frequency, and multiple receivers must isolate signals through antenna distributor.