【 Weak current College 】 how to properly use VHF and UHF wireless microphone

Wireless microphone because there is no transfer cable, easy to use, flexible and widely used. But if improper selection, often occur with intermittent, sound choppy signal, noise, sound quality is poor and not far from the transmission distance, produce, such as the main reason is not based on field and use the correct selection of wireless radiation of wavelengths and the correct method of installation.
The widespread adoption of wireless microphones VHF (very high frequency) and UHF (ultra-high frequency) two transmission frequency band. VHF-band range 30MHz?? 300MHz, wavelength for 10m?? 1m, usually called "metric". UHF-band frequency range is 300MHz?? 3000MHz, wavelength for 1m?? 0.1m, commonly referred to as "decimeter". Both radio frequency is widely used for TV, FM radio, mobile phones, pagers, stock information machines, microwave communications and radar, etc. Channel extremely crowded.
A variety of radio wave propagation in the space of freedom, time and geographical constraints, frequency overlapping intersections, without constraints and regulations inevitably produce interactive, the world's radio waves using a uniform requirements, so that the interaction between them is minimal. Wireless microphone allowing use of the frequency range of requirements:
VHF frequency band for 169MHz?? Total occupancy 230MHz 61MHz frequency range, and 6-12 TV channels of the same frequency range. In 61MHz frequency range is divided into A, B, C three segments, namely: (A) for the VHF 169MHz?? 185MHz, VHF (B) for 185MHz?? 200MHz, VHF (C) to 200MHz.
UHF frequency band to 690MHz?? Total occupancy 960MHz 270MHz frequency range, and TV 35?? 68 channels can be set to the same extent as the hundreds of wireless microphone channels. If necessary, the frequency range you can also scale up, set more wireless radio channels.
VHF and UHF two band characteristics of radio wave propagation
VHF and UHF radio frequency signals of collectively (RF), but the UHF bandmaking greater use of direct radiation of electromagnetic waves, VHF band except the use of direct radiation of electromagnetic waves, the used part and diffraction of electromagnetic energy, therefore in the same transmitter power and transmission, the transmission distance can be further. The reason for this is:
(1) metal objects on electromagnetic wave propagation and reflection of the barrier
Metal objects on electromagnetic wave has a barrier and reflection effects. Barrier effect of electromagnetic waves emitted wavelength and the size of the metal objects. Electromagnetic waves of a wavelength less than the size of the metal objects, you will be subject to reflection, electromagnetic wave propagation. That is the higher the frequency, metal objects, the stronger the reflection of electromagnetic waves. If electromagnetic waves of a wavelength greater than the size of the metal objects, electromagnetic wave will bypass the metal barriers continue to spread (diffraction). Obviously UHF VHF of reflectance reflex more stronger.
(2) electromagnetic wave on the metal grid (or perforated metal plate) penetration capacity
Electromagnetic waves of a wavelength greater than metal hole distance between the grid, the diffraction of electromagnetic waves will pass, the lower the frequency, the longer wavelength longer wavelength, through the more metal grid.
(3) non-metallic body (such as the human body and walls) on the role of electromagnetic wave absorption
The higher the frequency of the electromagnetic wave, non-metallic body, the greater its absorption, electromagnetic wave propagation loss.
(4) the air temperature on the influence of electromagnetic wave propagation
The higher the frequency, the greater the electromagnetic wave propagation loss. Propagation loss is also proportional to the size of the humidity.
Wireless microphone signal quality and transmission distance
Wireless microphone signal quality directly affects the transmission distance. Signal quality (S/N) and transmit power and space field strength distribution, receivers and receiving antennas for quality, efficiency and outside interference sources is closely related to the situation.
(1) to solve the electromagnetic field intensity fluctuation of measures
Because indoor objects reflection and absorption of electromagnetic wave propagation in multiple ways, so that the space of the electromagnetic wave field strength promulgated very complex, some parts of the field strength is weak, some parts of the rendering area of the "shadow", or even become a corner. When the transmitter and receiving antenna distances frequently change, the undulation of the field is changed. When receiving antenna in a weak field locations, the "mute sound" points or poor sound quality. To do this, the wireless microphone receiver with dual antenna diversity reception technique (Diversity) and AGC AGC technology to give up. Diversity reception technique is set in a receiver with two sets of identical reception antennas and two receivers and one through built-in computer chip circuit automatically detects and automatically choose a stronger way to receive the signal as the received signal, in collaboration with AGC control, you can effectively resolve the "mute sound" point.
Unfortunately the market a lot of cheap fake double antenna wireless microphone receiver, these counterfeit products in addition to the two receive antenna, there are no diversity reception device, so you cannot solve the problem of the "mute sound".
(2) wireless microphone transmitter power
Increase transmit power to increase the transmission range for wireless microphones. But wireless microphone transmitter power from radio wave effects on the human body, power supply voltage of the battery life and interference to nearby devices, and other factors, market products are limited to transmitting power 2mW?? 50mW。 Due to technical reasons, of VHF frequency band of transmitting power than UHF transmitting power easier to do it, the price is cheaper.
(3), receive antenna
, Receive antenna type, length, and match status directly affect the antenna gain and efficiency. Efficient, receive antennas are 1/2 wavelength omnidirectional radiation dipole antenna (half-wave dipole antenna). If the length of the antenna and the wavelength is disproportionate, will directly affect the transmission distance. UHF of short wavelength, so the UHF antenna VHF antenna with than a shorter length, transmitter antenna easier to install.
(4) interference signal
Interference signal increases wirelessMicrophone output will make noise, serious wireless microphone does a for. Interference signals from industry interference, TV and radio signal interference and wireless microphone between adjacent channel interference and other radio frequency interference, etc.
Industry interference: including automobile ignition systems, radio and cleaners, glow discharge lamps (fluorescent lights, neon lights, high pressure mercury lamp). The majority of their interference in the VHF frequency band of spectrum.
TV, FM radio, information and mobile communications platform, transmit power, frequency range, VHF band interference is greater than on the UHF band interference. The solution is to first find the interference source frequency range, and then select use avoid these frequency wireless microphone channel.
More wireless microphone between adjacent channel interference: in many wireless microphone use, often encounter adjacent channel at the same time, if one channel of harmonics fall into another channel occurs adjacent channel interference, the solution is to choose to use a frequency interval of channels. VHF band can choose the number of channels, the UHF band can choose many intervals larger channel.
How to choose?
In the above two band wireless microphone performance compare, VHF-band wireless microphone advantages of 1?? 8 point disadvantage is: 9?? UHF-band 16 points; wireless microphone has the following advantages: 9?? 16 points, the drawback is: 1?? 8 point. Selection should be based on the use of occasions and their characteristics, the "strength", give full play to their greatest strengths.
In General, suitable for VHF hotels, Convention Center, Sports Hall (Hall), function rooms and teaching system suitable for radio and television; UHF, theatre performances and demanding, many group channel at the same time work wireless microphone system. But regardless of which band, choose dual antenna diversity reception technique of high-performance receiver will have better results and more clear sound. If you need to increase the transmission distance, the receiving antenna mounted to close off the transmitter, and (or) use the antenna amplifiers, not blind pursuit of increased transmitter power.