LNB AND LNBF

An LNB (Low Noise Block) is a device used in satellite communication systems that receives and amplifies the high-frequency signals transmitted by a satellite. The LNB is typically mounted on a satellite dish and converts the received signals into a lower frequency range that can be transmitted over a coaxial cable to a satellite receiver. 

An LNBF (Low Noise Block Downconverter with Feedhorn) is a type of LNB that includes a feedhorn, which is used to collect the incoming satellite signals and direct them to the LNB. The LNBF is commonly used in Direct-to-Home (DTH) satellite TV systems, where it is used to receive satellite TV signals and transmit them to a satellite receiver for decoding and display on a TV screen.

LNB

Low noise block downconverters (LNBs) are essential for reliable satellite communication – but not all LNBs are created equal. Some produce too much phase noise or degrade signal strength. Others stunt data rates or fail in extreme temperatures. How do you know if you’re getting a high quality, high performing LNB for your satellite terminal?

 Phase Noise

LNB phase noise (or phase jitter) is caused by the phase fluctuations of an oscillator – and can seriously impact the performance of your terminal. A low phase noise LNB is critical for minimizing bit error rate (BER), particularly with higher order modulation schemes that squeeze as much data out of the link as possible, such as 32 APSK used in DVB-S2 or up to 128 QAM for some Earth Observation systems.

Phase noise is measured at specific intervals from the carrier frequency – usually starting at 10 Hz and moving up to 1 MHz. Good phase noise LNBs have 10 kHz values of -85 dB-Hz. In other words, the phase noise value is 85 dB below the carrier value when measured 10 kHz away from the carrier frequency.

 2.Noise Figure

Noise figure is a measure of the additional noise an LNB adds to a system link. The more noise an LNB adds, the worse the signal strength becomes. Signal quality is typically measured as a carrier-to-noise ratio (CNR, C/No or C/N ratio) – and modems require a minimum C/N ratio to acquire a signal.

There is no such thing as a noise figure of zero. All LNBs add noise due to the electronics in the unit – and the higher the frequency, the higher the noise will be. What is a good LNB noise figure? Look for 1.5 dB for Ka-band frequencies, 0.8 dB for Ku and X-band, and 0.4 dB for C-band.

3. Gain

Signal gain – the extent to which an amplifier boosts the strength of the signal from the antenna – is not usually an issue as most LNBs come with a fixed gain value of about 60 dB. However, an LNB’s gain is important to consider in two key circumstances: when dealing with long interfacility links (IFL) or large, high-gain antennas.

With regards to IFL, the longer the cable that connects your outdoor satellite receiver to indoor routers or transmitters, the greater the signal loss. In these cases, an LNB that delivers higher gain is necessary.

With large antennas (e.g. at teleports) too much gain can be an issue. These antennas introduce large signal power to the first stage of an LNB, which can saturate the LNB and cause signal compression. When the signal is compressed, the output power no longer increases with the input power. This creates a non-linear response – which in turn produces signal distortion and harmonics. An LNB that can be customized for gain is critical in these circumstances.