What is the link? What is the modulator and demodulator

What is the link? What is the modulator and demodulator
One line communication system
One line communication system by the modulator, demodulator, directional coupler (Branch), mixer (distributor), trunk amplifier, high frequency cable and other components, the following are described in detail in this paper.
Modulator
The image signal into a high frequency carrier signal equipment said modulator, sometimes called the modulator system of equipment, factory a modulator corresponds to a fixed channel, change can not be used, using amplitude modulation (AM) mode.
Modulator must pay attention to two important problems in use, one is the input image signal, usually in the 1Vp-p ± 0.3 Vp-p. The image signal input voltage is too low so that the image effect in gray image sense level or even have a distorted image; image signal input voltage is too high so that the image contrast is too strong and will also cause the image sense level or even have a distorted image. Therefore, must adjust according to the actual situation to determine use, each modulator are left to adjust the input voltage of the potentiometer, use a small screwdriver adjustment, clockwise signal increases, and decreases.
The second is the image carrier output level (also known as the RF output level), different channel modulator maximum image carrier output level slightly different but generally in the 105 to 110dB range. Each modulator has output level adjustment potentiometer, adjustable range is 20dB, adjusted using a small screwdriver, clockwise output level increases, and decreases. The modulator output level system should be adjusted based on actual site conditions, a crucial step, the output level adjustment will cause interference for the system, the specific adjustment method in the third chapter.
Modulator far Sail Technology Limited production of two types of YF-T600/D, YF-T600-1A/AD, YF-T600-16, as shown in figure 1.1. The YF-T600-1A/AD model can provide 12V/500mA DC power supply using camera.
The demodulator
The image carrier return to the image signal device called the demodulator, sometimes called the back-end equipment in the system, a demodulator is equivalent to a television receiver, only a few of the display part. In order to restore the multi-channel image signal, each channel must use a demodulator alone, to facilitate the use of multiple demodulator together demultiplexer is called in the same chassis. Common demodulator has single road, 4 road, 8 Road, 12 road, 16 Road, the user can choose according to the actual need.
The function of receiving demodulator is divided into channel tunable (optional table) and fixed channel (not optional table) two. The former with TV as the channel search can receive any channel, the use of more flexible, while the latter cannot channel search, a modulator can only receive a fixed channel, in the factory has been determined, the use of which cannot be changed. Because the monitoring equipment in use do not like to watch TV programs often required for the station, so the latter can reduce some costs. Demodulator using requirement when input signal level is appropriate, the signal is too weak image will produce snowflakes interference signal is too strong, easy to cause the network interference or image distortions. General single channel demodulator input signal in 65dB; 4 at 68 dB, 8 at 72 dB; 12 at 73 dB, 16 at 75 dB and above.
Data signal modulation and demodulation
With a variety of control functions of the camera needs to provide control signals, generally use the RS-485 data control, in order to make the data signal can also be transported in the same cable, also must carry on the data signal modulation and demodulation, the frequency modulation, frequency range 1538MHz. Data modulation, demodulation made circuit board independent pluggable, easy to use.