Technical

Choose and application of cables --- 2

1.3 Coaxial cable

Coaxial cable is widely used in the transmission of audio and video. Its impedance is 75 and this is a standard number to the impedance nowadays(before impedance of 50 is also applied). Excellent coaxial cable is usually a bit more expensive than twisted pair. Because of its reliable phisical property, it can offer excellent performance in transmission. The frequency, resolution and valid transmission distance of sigals play critical role in the audio and vedio system.

1.4 Optic Cable

Optic Calbe is the best choice for long distance transmission. The simple principle of optic cable: Analog signals transfered to optic transmitter, after processing of circuit, voltage signal is changed into electric current signal, then luminotron is driven to work. The input electric singal is changed into optic signal. After adjusting, it is introduced into optic firber.

After transfering, the optic signal is changed into former electric source. And it will be output after being enlarged.

Optic cable transmission aviods a lot of faults caused by common cable transmission and have many excellent features:

Excellent anti-electromagnetic interference
While being transfering in long distance, the cable itself is a huge antenna. It may collects electromagnetic signals arround. Especially in the vedio system, such interferential signals will become noise in the display. The core of optic cable is glass, and the transfered signal is optical signal which is not easy to be interfered by electromagnetice signals.

Very small volume
Most optic firber is as large as people's hair.

Very low attenuation
Because optic firber is made of glass tube. It will not be affected by cable impedance and capacitive impedance.

High safety
Signal transfered by optic cable is not easy to be wiretapped. Though optic cable seems to be perfect for singal transmission, it has some disadvantages.

High price: optic cable, emitter and receiver are all expensive.

High labour cost: While cabling, a lot of people and special tools are needed. Though it has little lost in the transmitting, it has high attenuation while emitting and receiving. So in order to guarantee non loss tranmission, a lot of amplifier is needed and power should be kept steady.