Direct broadcast satellite (DBS) dishes use an LNBF (LNB with feedhorn), which integrates the antenna feedhorn with the low noise block converter (LNB). Small diplexers are often used to distribute the resulting IF signal (usually 950 to 1450 MHz) piggybacked in the same coaxial cable jacket which carries lower-frequency terrestrial television from an outdoor antenna. Another diplexer then separates the signals to the receiver of the TV set, and the integrated receiver/decoder (IRD) of the DBS set-top box.

Newer Ka band systems use additional IF blocks from the LNBF, one of which will cause interference to UHF and cable TV frequencies above 250 MHz, precluding the use of diplexers. The other block is higher than the original, up to 2.5 GHz, requiring the LNB to be connected to high-quality all-copper RG-6/U cables. This is in addition to higher electrical power and electrical current requirements for multiple dual-band LNBFs.

For some satellite Internet and free-to-air (FTA) signals, a universal LNB (Ku band) is recommended. Most North American DBS signals use circular polarization, instead of linear polarization, therefore requiring a different LNB type for proper reception. In this case, the polarization must be adjusted between clockwise and counterclockwise, rather than horizontal and vertical.

In the case of DBS, the voltage supplied by the set-top box to the LNB determines the polarization setting. With multi-TV systems, a dual LNB allows both to be selected at once by a switch, which acts as a distribution amplifier. The amplifier then passes the proper signal to each box according to what voltage each has selected. The newest systems may select polarization and which LNBF to use by sending DiSEqC codes instead. The oldest satellite systems actually powered a rotating antenna on the feedhorn, at a time when there was typically only one LNB or LNA on a very large TVRO dish.
[edit] Universal LNB

A universal LNB can receive both polarisations (Vertical and Horizontal) and the full range of frequencies in the satellite Ku band. Some models can receive both polarisations simultaneously (known as a quattro LNB and used with a multiswitch) through four different connectors Low/Hor, Low/Ver, High/Hor, High/Ver, and others are switchable (using 13 volt for Vertical and 17 or 18 volt for Horizontal) or fully adjustable in their polarisation (this is relatively rare as this requires a separate polarisor, and it's also not part of the Universal LNB specification).

Here is an example of Universal LNB specifications:

* LO: 9.75 / 10.6 (or rarely 10.75) GHz (the 10.6 GHz Oscillator is selected by applying a 22 kHz tone to the cable)
* Freq: 10.7 - 12.75 GHz (slightly wider for 10.75 GHz LOs)
* NF: 0.7 dB
* Polarisation: Linear

Standard North America Ku-band LNB

By covering a smaller frequency range an LNB with a better noise figure can be produced. Pay TV operators can also supply a single fixed polarization LNBF to save a small amount of expense.

Here is an example of a standard linear LNB:

* Local oscillator: 10.75 GHz
* Frequency: 11.7-13.2 GHz
* Noise figure: 1 dB typical
* Polarization: Linear

North America DBS LNB

Here is an example of an LNB used for DBS:

* Local oscillator: 11.25 GHz
* Frequency: 12.2-12.7 GHz
* Noise figure: 0.7 dB
* Polarization: Circular

C-band LNB

Here is an example of a North American C-band LNB:

* Local oscillator: 5.15 GHz
* Frequency: 3.4-4.2 GHz
* Noise figure: ranges from 25 to 100 kelvins (uses Kelvin ratings as opposed to dB rating).
* Polarization: Linear

Source wikipedia