Interference Effect Of Video Conference Types And Solving Methods
Video conferencing is the use of audio-video communication technology and equipment through the channel in two or more locations, meeting of a communication tool, it enables audio, video, text, data, graphics and text data and multimedia integrated processing and run in the same network, unified real-time transmission.
Transmits these signal cables if over strong electro-magnetic field, there will be disturbances superimposed on the signal. Longer cables, jamming was more obvious.
Way, kind of interference source and interference
In a video-conference system, impact noise in addition to video and audio system equipment and the thermal noise of the transmission line itself and overlaid on the continuity of "white noise" interference, according to the interference source can be divided into two broad categories, pulse and AC noise interference. Pulse interference due to pulse electromagnetic coupled into the channel of the device: motors, automobile engine spark plug ignition, interference of switching power supply will produce 60Hz-2MHz, interference of such harmonics fall into video and audio band; lightning, also 2KHz-100MHz noise of the universe impulse noise. AC noise interference is mainly due to the unreasonable design of ground system, potential difference exists between the different locations, making ground current loops caused by high voltage transmission lines and can also cause hum interference of AC electrified railway, such as exchange of interference of electric railway 50Hz pitch outside, and (2N+1) x50Hz and other odd harmonics.
In addition, according to outside interference sources of electromagnetic energy transmission and audio and video equipment coupling can be subdivided into radiation interference and conduction disturbances. Conduction interference is a circuit (including stray capacitance and inductance can be represented by lumped circuit element) to the affected device, such as pulse interference, hum interference, mainly by way of conduction in the disturbed equipment radiation interference function through an antenna, from space to the affected devices, such as high-voltage transmission line on the disturbed device interference.
The frequency range of the audio signal of the video conference system for 300Hz-3.4KHz, video signal bandwidth of 6MHz. Usually uses balanced means for transmission of audio signals, due to induced noise on the line have offset each other, much less interference, even without logging out. Video signals are usually transmitted imbalance, disturbances will be much more serious. Interference analysis of audio and video analysis of difference: for video interference, mainly starting from the disturbances into audio signals due to the large wavelength, communication building shielding effect is more obvious, in comparison, negligible radiation interference. Pulse rectifiers such as through the power of audio and video signal mechanism the same, solutions, therefore, audio interference discussed focus on the hum interference.
Second, video analysis and solutions
In practice, video cables are usually laid in the communication in the metal pipes in the building. Metal tube and building construction together with the skin, and sometimes still possible disruption of, on the monitors will see irregular lines scroll from top to bottom, this interference is generated by thyristor ignition impulses caused by interference. UPS power supply pulse waveform produced is more complex, it has besides rectifier ignition caused by the pulse inverter and its harmonics. Power rectifier and UPS power supply generated by the pulse of radiation is everywhere, but is mainly distributed in the meeting room through the AC power line communication, conduction disturbances.
1 AC noise interference suppression
AC noise interference is primarily because of current form a loop through conduction effects to the video device. You can do this through the transmission line transformers isolate the video source and the receiver.
2 radiation interference suppression
Modern power systems is itself a strong electromagnetic sources of interference, mainly by radiation of interference the frequency bands in communications equipment. To inhibit the effect of external high-voltage transmission lines using grounding, grounding methods there are two commonly used, are respectively as follows:
A. disperse grounding
Dispersed ground is the communication building lightning protection and grounding, power supply system earthing, communications equipment of all types of Earth as well as other equipment grounding connected to the separate earthing system, due to increasing ground systems, ground effects are often difficult to avoid potential coupling between dispersed ground easily causes interference. While increasing the height of the main building, which grounded the insecurity is also growing. When a facility was struck by lightning, easy to form an underground fight back, damage to other equipment.
B. Joint grounding
Also known as single-point grounding grounding method of joint, which all share a common grounding system "". Integrated with some of the following features:
(1) the grounding system of the building as a whole form a cage, for direct lightning, building on the same floor level uniformity; lightning, cage and frame structure of the building external calls the shielding effect of magnetic fields are also available 10-40dB;
(2) the General grounding resistance of combined grounding is very small, there is no coupling between grounding influence helps to reduce interference;
(3) save metal, small footprint.
Is not difficult to see that by using joint grounding can reduce external interference of high voltage transmission lines.
3 audio interference analysis and solutions
Audio signal input and output interfaces between devices, are available in both balanced and unbalanced: balance-double-differential, with strong suppression of common-mode interference, hum interference, commonly used for signal transmission of long distance or interference conditions. Unbalanced type-single single-ended type, used for close range or internal signal transmission between devices. AC noise interference suppression, the following points should be noted:
(1) avoid potential 2 signal ground wire directly between the different devices connected or ground loops may be formed.
(2) so as to avoid or reduce direct connection between two devices.
(3) partial shielding of electrical connections in a system, the signal ground or shield on the side of the system grounding.
(4) transmission mode of remote transmits a signal using balanced transformer. Balancing transformers on both ends, one end of the shielding grounded or loft didn't answer. Grounded shielding can play role in Ming electric bonding occurs also prevents electric shock accident. When grounding, balancing transformer can be insulated at both ends isolation, balancing transformer Centre ground can discharge static electricity.