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Attached to the feed is the LNB (low noise amplifier block downconverer); you will see a probe (post) inside the LNB throat and this probes receives the mechanically vibrating microwaves and converts it into electrical energy to be passed the LNB circuitry then on through the cable to the satellite receiver. Additional to accepting the signal from the feed, the function of the LNB is to both immediately amplify the weak satellite signals from space (received by the dish and passed through the feedhorn probe as gigahertz - a billion cycles per second) and to convert them to an intermediate frequency (megahertz - a million cycles per second) that can be used to travel efficiently thru the coaxial cable attached to the LNB at one end and to the satellite receiver at the other end. Summarizing, satellite frequencies are in the gigahertz (GHz) range and the LNB downconverter output is in the megahertz (MHz) range (the industry standard is to downconvert to the 950-1450MHz range though proprietary systems will use a different downconvert range); inside the satellite receiver, the signal is again downconverted and this time to the frequency range acceptable by your television. Note the downconverted frequencies are in a range, i.e. block, thus the term 'block downconverter'. With a block downconverter, for a twenty-four channel satellite, i.e. twelve transponders, for example, the output of the downconverter contains the information for either the twelve horizontal or the twelve vertical (or RHCP/LHCP) transponders depending on which polarity is being accepted by the feedhorn. Because all twelve channels (in this example of a twelve tranponder satellite) are being carried into the house at one time it is possible to connect multiple satellite receivers to the same satellite dish each with the capability to tune a different channel (a dual feed is used to bring both banks of transponder polarities into the house at the same time when multiple receivers are desired). Block downconversion allows independent channel selection from multiple TV's (each fitted with its own satellite receiver) though, of course, they have to watch the same satellite at the same time. The LNB coaxial cable is typically a 75ohm, RG-6 coaxial cable though for longer travel distances, over several hundred feet, a larger size cable, RG-11, is used because frequencies will attenuate (loose strength) over distance and the object is to deliver a strong signal to the receiver.
LNBs are rated in noise temperature - the lower the number the better. Noise temperature is a value that indicates the unavoidable, inherent level of background atomic (molecular) motion in an object and this inherent noise (called ambient noise) is in the microwave frequency range. The lower the noise figure, the less ambient noise an LNB injects into the received signal; the lower noise rating of an LNB, the weaker signals it can effectively process. For C-band satellite signals, the noise figure is in degrees kelvin; a value of 25 or lower is today's industry standard. For Ku-band signals, the noise figure is in dB; a value of 1.0 or lower is today's industry standard with 0.7s being very commonly available.. An important fact to remember, natural molecular motion within all matter generates random noise and this random noise 'infiltrates' communication signals so that a received signal must be strong enough to override (rise above) the noise floor created by natural molecular motion. Therefore, the lower noise figure an LNB is rated the weaker satellite signals it can process and thusly the smaller diameter satellite dish it can accomodate. Modern LNB design and circuit technology advancements have lowered the noise figure values of today's LNBs considerably from the early days of the industry so by applying the lowest rated LNB to your system, the better signal processing you will receive and the smaller dish you will need.
LNBs are rated in noise temperature - the lower the number the better. Noise temperature is a value that indicates the unavoidable, inherent level of background atomic (molecular) motion in an object and this inherent noise (called ambient noise) is in the microwave frequency range. The lower the noise figure, the less ambient noise an LNB injects into the received signal; the lower noise rating of an LNB, the weaker signals it can effectively process. For C-band satellite signals, the noise figure is in degrees kelvin; a value of 25 or lower is today's industry standard. For Ku-band signals, the noise figure is in dB; a value of 1.0 or lower is today's industry standard with 0.7s being very commonly available.. An important fact to remember, natural molecular motion within all matter generates random noise and this random noise 'infiltrates' communication signals so that a received signal must be strong enough to override (rise above) the noise floor created by natural molecular motion. Therefore, the lower noise figure an LNB is rated the weaker satellite signals it can process and thusly the smaller diameter satellite dish it can accomodate. Modern LNB design and circuit technology advancements have lowered the noise figure values of today's LNBs considerably from the early days of the industry so by applying the lowest rated LNB to your system, the better signal processing you will receive and the smaller dish you will need.
