What Is an LNB on a Satellite Dish?
The LNB is the small device on the end of a dish's arm that amplifies the faint satellite signal and converts it to a frequency your cable can carry.
If the reflector is the part everyone notices, the LNB is the part that does the electronic work. LNB stands for Low-Noise Block downconverter, and it sits at the focal point on the end of the dish's arm, facing back into the bowl. Almost every reception problem that is not caused by aim or cabling comes back to the LNB, so it is worth understanding well.
What the LNB does
The LNB performs two jobs at once. First, it amplifies the incredibly weak signal that the reflector has focused onto it, boosting it enough to be usable. It does this while adding as little electrical noise as possible, which is what "low-noise" refers to; any noise the LNB introduces gets amplified along with the signal, so a quiet LNB is a good LNB. Second, it converts, or downconverts, the very high satellite frequency to a much lower one. That is the "block downconverter" part: it shifts an entire block of frequencies down at once so the signal can travel along ordinary coaxial cable without fading away. To see where this fits in the overall signal path, see how satellite dishes work.
LNB versus LNBF
You will see both terms. Traditionally the feed horn, the flared collector, and the LNB were separate parts. On most modern home dishes they are combined into a single sealed unit properly called an LNBF (the F is for the integrated feed). In everyday use almost everyone calls it an LNB regardless, and this guide does too. When you shop for a replacement, either term will find the right part.
Why it must sit exactly at the focal point
The reflector concentrates all the signal it gathers onto one small spot. The LNB has to sit precisely at that spot, held there by the arm. If the arm is bent, or the LNB is loose in its holder or rotated to the wrong angle, the focused signal lands beside it and reception suffers even though nothing is technically broken. This is why you should never reposition an LNB casually, and why a knock to the arm can cause mysterious signal loss.
Skew and polarization
Satellite signals are polarized, meaning they are oriented in a particular direction, and many satellites reuse frequencies by transmitting some channels in one polarization and others at ninety degrees to it. The LNB has to be rotated, or skewed, to match. In most home systems the LNB electronically switches between horizontal and vertical polarization on command from the receiver, but the physical skew angle of the whole assembly still has to be set correctly during installation. Getting skew right is part of proper aiming, covered in our guide to azimuth, elevation, and skew.
Types of LNB
LNBs are built for specific frequency bands, so a Ku-band LNB will not work on a C-band dish and vice versa; the difference between those bands is explained in satellite dish frequency bands. Beyond that, they vary by how many outputs and feeds they carry:
- Single LNB: one output, feeding one receiver or tuner.
- Twin, quad, and octo LNBs: multiple independent outputs so several receivers or tuners can operate at once, each tuning independently.
- Multi-feed and monoblock LNBs: two or more LNBs on one holder, or one unit designed to receive from two nearby satellites without moving the dish.
How the LNB is powered
One detail that surprises newcomers is that the LNB has no power cable of its own. It draws low-voltage power up the same coaxial cable that carries the signal down, a neat arrangement that avoids running electricity to the roof. The receiver also uses small changes in that voltage, and a high-frequency tone, to command the LNB, telling it which polarization to select and which band to output. This is why a completely dead LNB can sometimes be traced to a cable or connector fault that is starving it of power rather than to the LNB itself.
Replacing an LNB
Swapping an LNB is one of the more approachable dish repairs, but it must go back in the exact same position, orientation, and skew as the old one, or you will trade an electronic fault for an alignment fault. Mark the position before you remove the old unit, and weatherproof the cable connection when you reconnect. If replacing the LNB does not restore the signal, the problem more likely lies in aim or cabling; work through our guide to fixing a weak or lost signal next.
The bottom line
The LNB is a small, weatherproof amplifier and frequency converter that turns a focused but feeble signal into something your cable and receiver can use. It is the most electronically active part of the dish, the most common part to fail, and one of the easiest to replace, which makes it well worth understanding.