Basic principles of video transmission over twisted pair

The basic principle of using twisted pair to transmit video signals is:

1. The usual video signal is an unbalanced video baseband signal, which is suitable for transmission in the unbalanced transmission cable such as coaxial cable. The twisted pair cable is a balanced transmission cable. It is precisely because of the balanced transmission and the twisted pair mode of the cable that the twisted pair transmission has a strong anti-interference ability, so it is necessary to use twisted pair to transmit video signals. The video signal must be converted into a balanced signal.

2. The video signal converted into balanced mode can be directly transmitted on the twisted pair cable, and it is not easily affected by various interference signals. When it comes to the monitoring terminal, since the input ports of most monitoring equipment such as video and display are unbalanced, it is necessary to convert the balanced signal transmitted over the twisted pair into an unbalanced signal. That is, to use twisted pair cables instead of video cables to transmit video signals, it is only necessary to add balanced/unbalanced converters (press-type terminals) at the front and rear ends of the cable.

3. The simplest converter is essentially a video mutual inductance coil wound in parallel on a magnetic ring with high magnetic flux and high bandwidth, which is often referred to as a passive converter. It only plays the role of balanced/unbalanced conversion. It is a passive device and will not bring new distortion or noise, but it will attenuate the signal to a certain extent.

4. When the video signal is transmitted on the twisted pair cable, the attenuation of the signal, especially the attenuation of the high frequency, is particularly serious, so the balanced video signal after the twisted pair transmission must be amplified by an amplifier circuit in general And in response to the attenuation of the signal, especially the high-frequency signal, it is boosted and restored, and then converted into an unbalanced signal for use by monitors and other downstream equipment. Usually this amplifier is called a twisted pair receiver, which plays the role of amplification and compensation. Generally, there are two adjustable potentiometers on it, which adjust the amplification gain of the entire amplifier and the compensation for high-frequency components according to the actual situation.