RG 6 U
RG 11 U
The maximum transmission distance of video m
270
455
550
The wave resistance, Ohm
75
Resistance DC, Om/100 meters, no more
3.48
2.15
0.41
RG 59 (analogue RC-75) is used in 95 per cent of cases, and only occasionally, for transmission over a distance of 300-500 meters, used Cables type RG 11. He did not dress in the standard connectors N S. So, after the cable entered the room with video equipment, it is reasonable to immediately connect it to an amplifier-distributor and whether to have RG 59.
For the execution of the cables are internal and external. Last, in turn, are many parameters describing resistance to external Environment: frost resistance, resistance to ultraviolet (sun) Lighting, suitability for direct zakapyvaniyu in the ground (usually the cables are laid in protective tubes), the presence of armored sheath to protect it from mechanical damage. Externally, the performance of more common types of cable RG 11.
Describe some more specific types of cables, which are not so often: a few (150) coaxial cables in a single envelope, often combined with several vitymi shielded pairs for the transmission of Governors signals and two or three wires for power supply. Private, but very useful case of this construction is a coaxial cable, combined with the two wires feeding.
Transfer video on the telephone line.
Often faced with the task of transferring signal for low-cost, possibly had previously laid lines communications, in particular, on the telephone switched line. Quality low-cost twisted-pair is not enough to secure, without distortion, transmission of video, telephone lines impose more severe restrictions on the strip transmitted signal: PBX miss no more than 3.5 kHz. Digital technology in principle makes it possible to solve such problems, but had to sacrifice something, usually resolution and frame rate (in this case say about speed update images). One frame digitized video, remembered and transmitted with through modems, and then digitized another frame, and so on. Clearly, that the transfer took a shot considerable time. Transmission black-and-white image 500 x 500 pixels 64 shades of gray-the-art modems will take 50 seconds. It is therefore not transmitted every frame. To reduce the transfer time frame, try, if possible, to reduce number transmitted points in frame (s permission) - in the systems videopodtverzhdeniya anxiety considered sufficient to transfer about 100 x 100 pixels 8 grayscale. Be sure to apply methods of digital data compression, that is two to three times to reduce transfer time frame.
The most perfect system not convey the whole picture, not each frame, but only changes the image as compared to the previous frame. As most of the background is fixed, then to reduce the amount of information to be transferred, by 5-7 times.
In any case, the upgrade image is about a second. But while you can use the entire global communications infrastructure and transfer the image.
In addition to conventional telephone lines, the same telephone companies are often able to provide a dedicated digital channel of 64 kbit / sec. In the more developed countries is quite common link ISDN, which also produced a series of video transmission equipment.
Fiber-optic systems.
Advantages of fiber optic systems as compared to the coaxial cable:
-high protection against electromagnetic interference,
-much greater length of the segment (or modulated signal is transmitted),
fiber-coaxial cable is less good,
-laid the cable is not possible to find a metal detector.
However, the camera rarely have access to connect fiber optic cable. It must include electrical transformers signal in the optical and then back. These converters require supplementary feeding.
Wireless systems.
An example of such systems -- videosender - low-powered transmitter, which connects your camcorder, a reception is in a normal home TV to any channel decimetre. A lack of - a small power, plus - no secret - a resident of nearby homes can receive the same signal.
The more advanced systems require special ranges and innovative methods of modulation, that precludes the interception without a special equipment. Normally used cm range. At such short wavelengths are used narrow antenna, which means less power and data transmission to almost zero the possibility of radio.
Special range of possible called infrared - to intercept requires very much a rare equipment, and orientation antenna (radiator) is shares a corner seconds. Important the dignity of the infrared range - not need to obtain licenses to use such transmitters. The main disadvantage of infrared systems are more sensitive to atmospheric disturbances - fog, snow, rain. The range of validity of such a system does not exceed 2 km.
Examples:
2υ0, 22 + TS (shielded cable 2 veins, white);
4υ0, 22 + TS (cable screens. 4 veins, white)
