A Low Noise BlockDown Converters or LNB is a critical devicemounted at the focal point of a dish antenna. They are used mainly for satellite communications to initially amplify the very small signals from the satellite and then down convert them to L Band to feed them to a nearby building housing the Modem Demodulator for Communications Traffic or to a dvb-s2 demodulatoror a Set Top Box for TV Reception.
Technically,it is a combination of Low Noise Amplifier,a frequency mixer fed by either an Internal or External Referencefollowed by an L Band Amplifier.
The term ‘Low Noise’is the main requirement of the first stage input amplifier device,as specified in either Noise Temperature orNoise Figure asthe units, in which the Low Noise is measured. The values of all these units can be interchanged, however, the most usedunit in Noise Temperature.
The lower the Noise Temperature, the better reception the LNB ensures. They are used on Communication Satcom bands: L, S, C, X, Ku and increasingly Ka Bands, TV Transmission is typically at Ku band with its 1m or smaller dishes replacing the Big C band dishes except in high rainfall areas, were heavy clouds in tropical storms can block Receptions of the higher frequencies.
The frequency of satellite TV broadcast now range from C Band at 4GHz to Ka band at 30GHz!
Theterm ‘Block’ in a Low Noise Block Downconverterdenotes, a block or set of microwave signals, received and‘down converted’ by the LNB into a low range of frequencies that can be interpreted by the dvb-s2 demodulator or modem.