What is an LNB?

The abbreviation LNB: Low Noise Block down-converter.   It does not mean to block low noise!

The LNB is the device installed in front of the satellite dish and is connected with a cable (or more) to your decoder.  The LNB receives the very low level microwave signal that is transmitted from the satellite, amplifies it, changes the signals to the right frequency band and sends it with the cable to the decoder/receiver.

The expression low noise refers the quality of the first (input) electronic circuit.  The quality is measured in units called;

  • Noise Temperature,
  • Noise Figure,
  • Noise Factor.

The Noise Figure and Noise Factor are converted into Noise Temperature.  An LNB with a low Noise Temperature is better than one with a high Noise Temperature.

Block refers to the conversion of a block of microwave frequencies received from the satellite that are changed to a lower block of frequencies before sending it to the decoder.

The simple (single) LNB contains one or more local oscillators, referred to as LO running frequencies.

A universal LNB (dual band) has two local oscillators,

  • One to receive and convert the low band signals.
  • The other to receive and convert the high band signals.

FTA channel example:

  • Frequency: 10.773
  • Polarization: H  (requires 18)
  • Symbol Rate: 22000
  • FEC: 5/6

We need to determine on what LO frequency our LNB is running for the channel.  (Our example = 10773)

This frequency should be entered into the decoder.  Inspect the label on your LNB as well.

Polarization note: (Our example = H)

  • The LNB requires 18 volt for Horizontal signals.
  • The LNB requires 13 volt for Vertical signals.

The decoder and LNB will control the above if the correct frequency is entered.

On some of the decoders:

  • The 22kHz setting on the decoder should be off for Low Band
  • The 22kHz setting on the decoder should be on for High Band

A few LNB models;

  • A simple LNB with one LO frequency
  • Dual-band LNBs
    These will typically have two alternative local oscillator frequencies
  • Dual polarization LNBs
    Dual polarization LNBs may commonly be switched remotely using e.g. 13 volts for vertical polarization and 18 volts for horizontal polarization.
  • Multi-LNBs
    A “Quad LNB” might have 4 outputs, for each polarization and each of two bands.

Overloading an LNB

If you have a very large dish intended for reception by small diameter dish, the increase in total power of the signals into the LNB may be sufficient to overload some of the electronics.

Other information.

  • Symbol rate (Our example = 22000)

Symbol rate is the indication of the carrier modulation speed. Symbol rate tells how many transmission symbols are modulated to the carrier per second.  It is the rate of state changes on a communications circuit.

Symbol rate dependents primarily on the modulation rate and channel width. If a circuit can carry two tones per second, the circuit has a symbol rate of two. The symbol rate is also known as the baud rate.

  • FEC (Our example = 5/6)

Forward Error Correction is a type of error correction which improves on error detection by enabling the receiver to correct errors once they are detected. This reduces the need for retransmissions.

  • A transponder

A transponder is a wireless communication device that picks up an incoming signal and response to it. Transponder is a combination of the two words transmitter and responder

Previous articleWhat is Free-to-Air (FTA)?
Next articleWhat is the meaning of a satellites footprint (coverage)?
Ockert J van Nieuwenhuizen
Based in South Africa, Ockert J van Nieuwenhuizen is a satellite broadcast techie and has written a number of articles on tech.africa


  1. Hi
    I have a satellite dish with four connections
    I want to take one out and replace it with a different cable for a different TV
    The LNB I can see but I don’t know how to get at the connection to pull or screw out the cable connection and as I have nueritis in the knees I find it hard to get on my knees. I don’t want to use force as the old dish is peeling its surface but works ok for our TV I.m 79 years and I could get my son to go on the store roof if I could tell him what to do
    any chance of your good news on how to change say the coaxial cable I know how to prepare it for the screw connection and both ends may be the same

    Happy Xmas anyway
    Signed James Butler 6 REnmore Crescent Galway 091 756212

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.