time:2019-05-18|
reading volume:1126|
source:admin 【】
the receiving antenna of wireless microphone is one of the most misunderstood areas. errors in antenna selection, layout and wiring may lead to short performance coverage areas and low signal intensity, leading to frequent dropouts. the performance of modern diversity receivers is much better than that of single antenna types, but in order to optimize the system performance and reliability, the antenna selection and layout must be correct.
solution: to ensure good diversity of the system, the antenna space should be at least one and a half wavelength (about 9 inches 700 mhz). the angle of receiving antenna should be "v" configuration, which can provide better signal pickup performance when the transmitter moves or is placed at different angles. if the receiver is to be installed away from the performance area (e.g. in a closet or enclosed rack), a half-wave antenna or a directional antenna (preferably above the audience) should be installed remotely so as to have a clear line of sight between transmitters. do not install hf antennas remotely because they use receiver chassis as ground antenna. redundant distances between antennas will not significantly improve the diversity of the system, but may better cover a larger area of stage, church or conference room. if the antenna is installed far away from the stage, the directional antenna can be used to improve the signal reception by picking up more signals in this direction and reducing other angle signals picking up. if the coaxial cable is used to connect the antenna to the receiver, it may be necessary to use the antenna amplifier to solve the problem of signal loss in cable transmission. the loss of signal quantity depends on the specific length of cable and cable type. therefore, please calculate according to the manufacturer's suggestion. the total net loss of signal should be controlled within 5db.
artificial radio signal blocked
the human body may also interfere with wireless signals. the human body is mainly composed of a large amount of water, which can absorb radio frequency energy. in addition, if the user surrounds the hand on the external antenna of the portable 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 be affected.
solution: keep the transmitter antenna fully deployed and unobstructed, so as to achieve better performance in a wide range of signal transmission.
insufficient voltage of emitter battery
the battery life of the transmitter is the primary concern of the wireless microphone. users always try to reduce the cost of equipment by using low-cost batteries. most wireless manufacturers specify alkaline batteries or disposable lithium batteries because their output voltages are stable throughout the battery life cycle. this is very important because most transmitters suffer from acoustic distortion or signal loss at low voltage. rechargeable batteries often seem to be the ideal solution, but most rechargeable batteries provide 20% lower voltage than disposable batteries even if they are fully charged.
solution: in order to solve the problem of batteries, we should carefully compare the voltage output requirements of emitter batteries at any time to ensure the sustainability of batteries in the whole working process. lithium-ion batteries and rechargeable alkaline batteries can usually work continuously, while nickel-hydrogen and nickel-cadmium batteries may last only a few hours. the performance of aa rechargeable battery is similar to that of disposable aa battery.
unadjustable transmitter
the inherent noise and limited dynamic range of fm transmission make analog wireless audio transmission limited. to overcome this, most wireless microphone systems usually use two audio processing methods to improve the sound quality. pre-weighting device is added to transmitter and de-weighting device is added to receiver to improve signal-to-noise ratio. the compressor and receiver expander in the transmitter can increase the dynamic range to over 100 db. this makes 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: in order to obtain better sound quality, the input gain of the transmitter should be adjusted so that the overall modulation occurs at higher volume without distortion.
the setting of wireless system
the most troubling problem in wireless systems is the constant change of radio waves themselves. since the beginning of digital tv conversion, analog and digital tv channel radio waves have been changing. the fcc is trying to find a way to make consumer products (personal pdas, smart phones or home devices) use empty television channels for wireless internet access.
solution: it was easy to know that the vhf channel in the user's city was odd or even. however, when people install and use wireless microphones (as well as ear-in monitors and intercom systems, etc.), they have to check the local spectrum regularly even when they work in familiar locations.
error setting of receiver output level
with so much discussion on frequency, wavelength and antenna, it is easy to overlook the basic requirements of wireless microphone systems: in order to replace the connection cables between signal sources and audio systems, receivers are usually equipped with output level control, while most wired microphones do not. this provides a better opportunity for finer matching between receiver output and input.
solution: whether the microphone level or the line level, the output level should be set to a practical higher level, and at the same time not exceed the input limit of the audio system. this may be indicated in the input channel of the mixer, or can be judged by the distortion of the audio.