Learn about cable TV systems: headend and modulator

“A television network available via direct cable channel, available through satellite broadcast, as well as via IPTV channel.”

  Cable TV is also known as “CATV” (community antenna television). In addition to bringing television programs to those millions of people throughout the world who are connected to a community antenna, cable TV will likely become a popular way to interact with the World Wide Web and other new forms of multimedia information and entertainment services.

Cable Television Network diagram

Cable Television Network diagram

Cable Television Network diagram

  1. Most cable TV systems also carry local over-the-air television stations for distribution.
  2. Some cable TV systems receive the local television stations’ programming by dedicated coaxial, microwave link or fiber-optic line, installed between the local station and the headend.
  3. Other sources of programming include those delivered via fiber optics, telephone wires, the Internet, microwave towers and local public-access television channels that are sent to the cable headend on an upstream frequency over the cable system itself (known in the industry as “T”-channels), or via a dedicated line set up by the cable company, for reception of local television stations’ programming by the headend.

Cable television headend and modulator

  A cable television headend is a master facility for receiving television signals for processing and distribution over a cable television system. The headend facility is normally unstaffed and surrounded by some type of security fencing and is typically a building or large shed housing electronic equipment used to receive and re-transmit video over the local cable infrastructure. One can also find head ends in power line communication (PLC) substations and Internet communications networks.

Cable television signals are then mixed in accordance with the cable system’s channel numbering scheme using a series of cable modulators (one for each channel), which is in turn fed into a frequency multiplexer or signal combiner. The mixed signals are sent into a broadband amplifier, then sent into the cable system by the trunk line and continuously re-amplified as needed.

Modulator Equipment introduction

A device called a modulator at the local station’s facilities feed their programming over this line to the cable TV headend, which in turn receives it with another device called a demodulator. It is then distributed through the cable TV headend to subscribers. This is usually more reliable than receiving the local stations’ broadcasts over the air with an antenna.
24 in 1 Fixed Channel Modulator

24 in 1 Fixed Channel Modulator

This 24 channels module type modulator is low cost and high stability, specially designed for MATV or SMATV system. Professional design with simple installation. It is easily operated or maintained by users.

  • 1 set can install 24 channels. Adjacent channel workable.
  • Individual function keys for each channel, simple operation.
  • High efficiency SMPS enable stable performance.
  • All the figures already pre-set in the factory. No further adjustment to the modulator in case of necessary.
  • Easy setup,Internal fans for cooling modulators
  • Only one RF output. No need combiner
  • Precise frequency control with PLL circuitry
  • Also available in NTSC,all PAL configuration
  • 19” rack mountable.

Modulator Equipment Specifications

Frequency Range 47 ~ 860MHz (Any one channel)
Output Level ≥105dBμV
Output Level Adjustment Range 0 ~ -20dB (Variable)
Video to Audio Carrier -10dB ~ -30dB adjustable
Output Impedance 75Ω
Spurious Output Suppression ≥60dB
Frequency Accuracy ≤±5KHz (VHF) , ≤±10KHz (UHF)
Video Output Reflection ≥12dB (VHF) ; ≥10dB (UHF)
Video Input Level 1.0Vp-p (87.5% Modulation)
Video Input Impedance 75Ω
Differential Gain ≤5% (87.5% Modulation)
Differential Phase ≤5° (87.5% Modulation)
C/L Delay ≤45 ns
Flatness ±1dB
Video Modulator Depth 0 ~ 90% (Variable)
Video S/N ≥55dB
Audio Input Level 1Vp-p (±50KHz)
Audio Input Impedance 600Ω
Audio S/N ≥57dB
Audio Pre-weighted 50μs
Power Supply AC 110V/220V±10% 50Hz±2Hz , 50W
Working Temperature0 ~ 40 ℃
Dimensions19 Inch 4 U housing

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