LNBs

LNBs, or low-noise block downconverters, are a key component of satellite television reception. Mounted on the focal point of a parabolic dish, an LNB receives microwave signals from the dish and converts them to a lower intermediate frequency (IF) that can be carried by coax to a satellite receiver. The downconverted signal is typically in the 950 to 2150 MHz range, while the incoming RF is in the Ku-band (and sometimes Ka- or C-band) depending on the system.

An LNB combines three main functions: a low-noise microwave amplifier to boost weak signals, a mixer to perform downconversion, and a local oscillator to provide the downconversion frequency. Additional filtering and shielding help minimize noise and spurious signals. The resulting IF output is then routed to one or more satellite receivers.

LNBs come in several configurations. A standard single-output LNB feeds one receiver; multi-output variants (dual, quad, or octo) provide several IF ports for multiple tuners or receivers. Universal or wideband LNBs can receive a broader range of transponder bands and satellites by switching LO frequencies. Some designs, known as monoblock or two-satellite LNBs, combine signals from two adjacent satellites on a single dish using two LO references.

Power and polarization control: LNBs are powered by a DC supply from the receiver or an external source, typically around 13 to 18 volts. Polarization is controlled by voltage: around 13 V for vertical and 18 V for horizontal, though many modern LNBs use internal polarization schemes and do not rely on this signaling in the same way.

Key performance specs include noise figure, gain, and LO stability. Reliability is influenced by weather exposure, moisture protection, and build quality.