Direct broadcast satellite (DBS) dishes use an LNBF (NB feedhorn), which integrates the antenna feedhorn with the LNB. Small diplexers are often used to distribute the resulting IF signal (usually 950 to 1450 MHz) piggybacked in the same cable TV wire that 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 polarisation 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.
