Voltages and Signals

• LNBs focus on two satellites above the Earth. Each satellite sends digital signals from up to 32 transponders, and each transponder carries up to eight different broadcast network programming. When you view television and select a particular broadcast network from the receiver's guide menu, the satellite receiver talks to the LNB and tells it which satellite, transponder and program to select. It does so by sending either an 18-volt DC or a 13-volt DC signal to the LNB, along with a 22-hertz tone. Together, these voltages and tones "change the channel" in the satellite dish's LNB.
  
  

18-Volt Control Current

• In addition to the variables described above, the digital signal is also oriented vertically and horizontally as it travels to earth. Imagine a helical spring toy shaped like an oval rather than a perfect circle; the satellite signal travels to Earth, spinning in this oval pattern. When the oval pattern for a particular transponder is aligned vertically, the LNB receives an 18-volt current telling it to look for a vertically aligned digital signal.
  
  

13V-Volt Control Current

• In the same way the LNB looks for a vertically aligned digital signal when it receives an 18-volt signal from the receiver, the LNB switches and looks for a horizontally aligned signal when it receives a 13-volt current from the receiver in the home. Digital frequencies close to one another alternate in their pattern from vertical to horizontal alignment so the signals do not bleed over onto one another.
  
  

22-Hertz Tone

• In addition to the two voltages, a 22-hertz tone, or radio wave, travels between the satellite receiver in the home and the LNB outside the home. This tone is constant, and it tells the LNB which satellite to "look for." A dual LNB receives signals from two satellites at all times. Each satellite broadcasts programming from a number of individual networks. When you change channels inside the home, the LNB contains a built-in multiswitch that allows it to switch from one satellite to another to find the network you selected. The 22-hertz tone controls the multiswitch and tells the LNB when to switch between satellites.