Low-noise block downconverter
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A low-noise block downconverter (LNB) is the receiving device mounted on
The LNB is a combination of low-noise amplifier,
The LNB is usually a small box suspended on one or more short booms, or feed arms, in front of the dish reflector, at its focus (although
The LNB gets its power from the receiver or set-top box, using the same coaxial cable that carries signals from the LNB to the receiver. This phantom power travels to the LNB; opposite to the signals from the LNB.
A corresponding component, called a
Amplification and noise
The signal received by the LNB is extremely weak and it has to be amplified before downconversion. The low-noise amplifier section of the LNB amplifies this weak signal while adding the minimum possible amount of noise to the signal.
The low-noise quality of an LNB is expressed as the
Every LNB off the production line has a different noise figure because of manufacturing tolerances. The noise figure quoted in the specifications, important for determining the LNB's suitability, is usually representative of neither that particular LNB nor the performance across the whole frequency range, since the noise figure most often quoted is the typical figure averaged over the production batch.
Block downconversion
Satellites use comparatively high
The purpose of the LNB is to use
The frequency conversion is performed by mixing a fixed frequency produced by a local oscillator inside the LNB with the incoming signal, to generate two signals equal to the sum of their frequencies and the difference. The frequency sum signal is filtered out and the frequency difference signal (the IF) is amplified and sent down the cable to the receiver:
- C-band
- Ku-band
where is a frequency.
The local oscillator frequency determines what block of incoming frequencies is downconverted to the frequencies expected by the receiver. For example, to downconvert the incoming signals from Astra 1KR, which transmits in a frequency block of 10.70–11.70 GHz, to within a standard European receiver's IF tuning range of 950–2,150 MHz, a 9.75 GHz local oscillator frequency is used, producing a block of signals in the band 950–1,950 MHz.
For the block of higher transmission frequencies used by Astra 2A and 2B (11.70–12.75 GHz), a different local oscillator frequency converts the block of incoming frequencies. Typically, a local oscillator frequency of 10.60 GHz is used to downconvert the block to 1,100–2,150 MHz, which is still within the receiver's 950–2,150 MHz IF tuning range.[6]
In a C-band antenna setup, the transmission frequencies are typically 3.7–4.2 GHz. By using a local oscillator frequency of 5.150 GHz the IF will be 950–1,450 MHz which is, again, in the receiver's IF tuning range.
For the reception of
Low-noise block feedhorns (LNBFs)
With the launch of the first DTH broadcast satellite in Europe (
The Astra type LNBF that includes a feedhorn and polarizer is the most common variety, and this is fitted to a dish using a bracket that clamps a collar around the waveguide neck of the LNB between the feedhorn and the electronics package. The diameter of the LNB neck and collar is usually 40mm although other sizes are also produced. In the UK, the "minidish" sold for use with
LNBs without a feedhorn built-in are usually provided with a (C120) flange around the input waveguide mouth which is bolted to a matching flange around the output of the feedhorn or polarizer unit.
Polarization
It is common to polarize satellite TV signals because it provides a way of transmitting more TV channels using a given block of frequencies. This approach requires the use of receiving equipment that can filter incoming signals based on their polarization. Two satellite TV signals can then be transmitted on the same frequency (or, more usually, closely spaced frequencies) and provided that they are polarized differently, the receiving equipment can still separate them and display whichever one is currently required.
Throughout the world, most satellite TV transmissions use vertical and horizontal
The probe inside the LNB waveguide collects signals that are polarized in the same plane as the probe. To maximise the strength of the wanted signals (and to minimise reception of unwanted signals of the opposite polarization), the probe is aligned with the polarization of the incoming signals. This is most simply achieved by adjusting the LNB's skew; its rotation about the waveguide axis. To remotely select between the two polarizations, and to compensate for inaccuracies of the skew angle, it used to be common to fit a polarizer in front of the LNB's waveguide mouth. This either rotates the incoming signal with an electromagnet around the waveguide (a magnetic polarizer) or rotates an intermediate probe within the waveguide using a servo motor (a mechanical polarizer) but such adjustable skew polarizers are rarely used today.
The simplification of antenna design that accompanied the first Astra DTH broadcast satellites in Europe to produce the LNBF extended to a simpler approach to the selection between vertical and horizontal polarized signals too. Astra type LNBFs incorporate two probes in the waveguide, at right angles to one another so that, once the LNB has been skewed in its mount to match the local polarization angle, one probe collects horizontal signals and the other vertical, and an electronic switch (controlled by the voltage of the LNB's power supply from the receiver: 13 V for vertical and 18 V for horizontal) determines which polarization is passed on through the LNB for amplification and block-downconversion.
Such LNBs can receive all the transmissions from a satellite with no moving parts and with just one cable connected to the receiver, and have since become the most common type of LNB produced.
Common LNBs
C-band LNB
Here is an example of a North American C-band LNB:
- Local oscillator: 5.15 GHz
- Frequency: 3.40–4.20 GHz
- Noise temperature: 25–100 kelvins (uses kelvin ratings as opposed to dB rating).
- Polarization: Linear
Supply voltage |
Block | Local oscillator frequency |
Intermediate freq. range | |
---|---|---|---|---|
Polarization | Frequency band | |||
13 V | Vertical | 3.40–4.20 GHz | 5.15 GHz | 950–1,750 MHz |
18 V | Horizontal | 3.40–4.20 GHz | 5.15 GHz | 950–1,750 MHz |
Ku-band LNB
Standard North America Ku band LNB
Here is an example of a standard linear LNB:
- Local oscillator: 10.75 GHz
- Frequency: 11.70–12.20 GHz
- Noise figure: 1 dB typical
- Polarization: Linear
Supply voltage |
Block | Local oscillator frequency |
Intermediate freq. range | |
---|---|---|---|---|
Polarization | Frequency band | |||
13 V | Vertical | 11.70–12.20 GHz | 10.75 GHz | 950–1,450 MHz |
18 V | Horizontal | 11.70–12.20 GHz | 10.75 GHz | 950–1,450 MHz |
Universal LNB ("Astra" LNB)
In Europe, as
The launch of
A Universal LNB has a switchable local oscillator frequency of 9.75/10.60 GHz to provide two modes of operation: low band reception (10.70–11.70 GHz) and high band reception (11.70–12.75 GHz). The local oscillator frequency is switched in response to a 22 kHz signal superimposed on the supply voltage from the connected receiver. Along with the supply voltage level used to switch between polarizations, this enables a Universal LNB to receive both polarizations (Vertical and Horizontal) and the full range of frequencies in the satellite Ku band under the control of the receiver, in four sub-bands:[7]
Here is an example of a Universal LNB used in Europe:
- Noise figure: 0.2 dB typical
- Polarization: Linear
Supply | Block | Local oscillator frequency |
Intermediate freq. range | ||
---|---|---|---|---|---|
Voltage | Tone | Polarization | Frequency band | ||
13 V | 0 kHz | Vertical | 10.70–11.70 GHz, low | 9.75 GHz | 950–1,950 MHz |
18 V | 0 kHz | Horizontal | 10.70–11.70 GHz, low | 9.75 GHz | 950–1,950 MHz |
13 V | 22 kHz | Vertical | 11.70–12.75 GHz, high | 10.60 GHz | 1,100–2,150 MHz |
18 V | 22 kHz | Horizontal | 11.70–12.75 GHz, high | 10.60 GHz | 1,100–2,150 MHz |
North America DBS LNB
Here is an example of an LNB used for
- Local oscillator: 11.25 GHz
- Frequency: 12.20–12.70 GHz
- Noise figure: 0.7 dB
- Polarization: Circular
Supply voltage |
Block | Local oscillator frequency |
Intermediate freq. range | |
---|---|---|---|---|
Polarization | Frequency band | |||
13 V | Right-hand | 12.20–12.70 GHz | 11.25 GHz | 950–1,450 MHz |
18 V | Left-hand | 12.20–12.70 GHz | 11.25 GHz | 950–1,450 MHz |
Ka band LNB
Here are examples of Ka band LNBs:
Supply voltage |
Block | Local oscillator frequency |
Intermediate freq. range | |
---|---|---|---|---|
Polarization | Frequency band | |||
13 V | Right-hand | 20.2–21.2 GHz | 19.25 GHz | 950–1,950 MHz |
18 V | Left-hand | 20.2–21.2 GHz | 19.25 GHz | 950–1,950 MHz |
13 V | Right-hand | 21.2–22.2 GHz | 20.25 GHz | 950–1,950 MHz |
18 V | Left-hand | 21.2–22.2 GHz | 20.25 GHz | 950–1,950 MHz |
Here is an example of a Norsat Ka band LNB:
Supply voltage |
Block | Local oscillator frequency |
Intermediate freq. range | |
---|---|---|---|---|
Polarization | Frequency band | |||
13 V | Right-hand | 18.2–19.2 GHz | 17.25 GHz | 950–1,950 MHz |
18 V | Left-hand | 18.2–19.2 GHz | 17.25 GHz | 950–1,950 MHz |
S band LNB
Here is an example of an S band LNB:
- Local oscillator: 1.57 GHz
- Frequency: 2.52-2.67 GHz
- Noise temperature: Maximum of 50 kelvins (uses kelvin ratings as opposed to dB rating).
- Polarization: Linear
Supply voltage |
Block | Local oscillator frequency |
Intermediate freq. range | |
---|---|---|---|---|
Polarization | Frequency band | |||
13 V | Vertical | 2.52-2.67 GHz | 1.57 GHz | 950–1,100 MHz |
18 V | Horizontal | 2.52-2.670 GHz | 1.57 GHz | 950–1,100 MHz |
This frequency range of LNB is quite rare as the only direct broadcast satellites that work with the S-band frequency are IndoStar-1 and IndoStar-2, both utilized by Indonesian direct-to-home provider MNC Vision. S-band was chosen for these satellites because its frequencies efficiently penetrate the atmosphere and provide high-quality transmissions to small-diameter 80 cm antennas in regions that experience heavy rainfall such as Indonesia. A similar Ku- or C-band reception performance requires greater transmission power or much larger dish to penetrate the moist atmosphere.
Multi-output LNBs
Dual, twin, quad, and octo LNBs
An LNB with a single feedhorn but multiple outputs for connection to multiple tuners (in separate receivers or within the same receiver in the case of a twin-tuner PVR receiver). Typically, two, four or eight outputs are provided. Each output responds to the tuner's band and polarization selection signals independently of the other outputs and "appears" to the tuner to be a separate LNB. Such an LNB usually may derive its power from a receiver connected to any of the outputs. Unused outputs may be left unconnected (but waterproofed for the protection of the whole LNB).
Note: In the US an LNB with two outputs is termed a "dual LNB", but in the UK the term "dual LNB" historically described an LNB with two outputs, each producing only one polarisation, for connection to a multiswitch (the term and the LNBs fell out of use with the introduction of the Universal LNB and the multiswitch equivalent, the quattro LNB – see below). Today "dual LNB" (and "dual feed") describes antennas for reception from two satellite positions, using either two separate LNBs or a single Monoblock LNB with two feedhorns. In the UK, the term "twin-output LNB", or simply "twin LNB", is usually used for an LNB with a single feedhorn but two independent outputs.[3]
Quattro LNBs
A special type of LNB (not to be confused with Quad LNB) intended for use in a shared dish installation to deliver signals to any number of tuners. A quattro LNB has a single feedhorn and four outputs, which each supply just one of the Ku sub-bands (low band/horizontal polarization, high band/vertical polarization, low/vertical and high/horizontal) to a multiswitch or an array of multiswitches, which then delivers to each connected tuner whichever sub-band is required by that tuner.[8]
Although a quattro LNB typically looks similar to a quad LNB, it cannot (sensibly) be connected to receivers directly. Note again the difference between a quad and a quattro LNB: A quad LNB can drive four tuners directly, with each output providing signals from the entire Ku band. A quattro LNB is for connection to a multiswitch in a shared dish distribution system and each output provides only a quarter of the Ku band signals.
Satellite channel router (SCR), or unicable LNBs
Multiple tuners may also be fed from a
Instead of block-downconverting the whole received spectrum, an SCR LNB downconverts a small section of the received signal (equivalent to the bandwidth of a single transponder on the satellite) selected according to a DiSEqC-compliant command from the receiver, to output at a fixed frequency in the IF. Up to 32 tuners can be allocated a different frequency in the IF range and for each, the SCR LNB downconverts the corresponding individually requested transponder.[9]
Most SCR LNBs also include either a legacy mode of operation or a separate legacy output which provides the received spectrum block-downconverted to the whole IF range in the conventional way.
Wideband LNB
ASTRA Universal Wideband LNBs with an oscillator frequency of 10.40 or 10.41 GHz are entering the market. The intermediate frequency band is much wider than in a conventional LNB, as the high and low band are not split up.
Wideband LNB signals can be accepted by new wideband tuners, and by new SCR systems (e.g., Inverto/Fuba,[10] Unitron,[11] Optel,[12] GT-Sat/Astro), with or without optical transmission. Wideband signals can be converted to conventional quattro signals[13] and vice versa.[14]
In February 2016, Sky (UK) launched a new LNB only compatible with their new wideband tuner.[15] This LNB has one port for all vertical polarised channels both low and high band, and another port for all low and high band horizontal channels. The basic model has only 2 connections and presumably has a local oscillator of 10.41 GHz with an intermediate frequency of 290–2340 MHz from an input of 10.7–12.75 GHz. This LNB seems to be the same as Unitron's ASTRA Universal Wideband LNB.[16] Two cables minimum are needed to access all channels. In the Sky Q box, multiple tuners can select multiple channels, more than the usual two for dual coax systems. This type of LNB is incompatible with the more common Astra Universal LNB used in the UK meaning the LNB is changed during upgrade. There is a model of the LNB with 6 connections, 2 for Sky Q and 4 Astra Universal LNB for users with multiple legacy systems such as Freesat in addition to Sky Q. In cases where only a single cable is possible, such as apartment blocks, Sky Q compatible multiswitches can be used, which instead use BSkyB SCR.[17]
Optical-fibre LNBs
LNBs for
At the receiver, the optical signal is converted back to the traditional electrical signal to "appear" to the receiver as a conventional LNB.[18]
Monoblock LNBs
A monoblock (or monobloc) LNB is a single unit comprising two, three or four LNBs and a DiSEqC switch, designed to receive signals from two, three or four satellites spaced close together and to feed the selected signal to the receiver. The feedhorns of the two LNBs are at a fixed distance apart for reception of satellites of a particular orbital separation (often 6°, but also 4°). Although the same functionality can be achieved with separate LNBs and a switch, a monoblock LNB, constructed in one unit, is more convenient to install and enables the two feedhorns to be closer together than individually cased LNBs (typically 60mm diameter). The distance between the feedhorns depends on the orbital separation of the satellites to be received, the diameter and focal length of the dish used, and the position of the reception site relative to the satellites. So monoblock LNBs are usually a compromise solution designed to operate with standard dishes in a particular region.[19] For example, in parts of Europe, monoblocks designed to receive the Hot Bird and Astra 19.2°E satellites are popular because they enable reception of both satellites on a single dish without requiring an expensive, slow and noisy motorised dish. A similar advantage is provided by the duo LNB for simultaneous reception of signals from both the Astra 23.5°E and Astra 19.2°E positions.
There are also available triple monoblock LNB units, which enable users to receive three satellites:
for example Hotbird 13°E, Eutelsat 16°E and Astra 19.2°E or the same can be used for positions: Eutelsat 7°E, Eutelsat 10°E and Hotbird 13°E. This monoblock can be used for other positions with the same spacing (3°+3°=6°spacing).
Other very popular example for different spacing is: Astra 1: 19.2°E, Astra 3: 23.5°E and Astra 2: 28.2°E (4.3°+4.7°=9°spacing).
And there are also available four feed monoblock LNB units, which enable users to receive signals from four satellites, for example
Most receivers sold nowadays are compatible with at least
Cold temperatures
It is possible for moisture in an LNB to freeze, causing ice to build-up at very low temperatures. This is only likely to occur when the LNB is not receiving power from the satellite receiver (i.e., no programmes are being watched). To combat this, many satellite receivers provide an option to keep the LNB powered while the receiver is on standby. In fact, most LNBs are kept powered because this helps to stabilise the temperature and, thereby, the local oscillator frequency by the dissipated heat from the circuitry of LNB. In the case of UK
See also
- Bias tee
- Block upconverter (BUC)
- Orthomode transducer
- Signal-to-noise ratio
- Transmit and receive integrated assembly (TRIA)
- Duo LNB
- Single Cable Distribution
- Fibre satellite distribution
References
- ^ "Glossary of Satellite Terms". Satnews.com. Archived from the original on July 10, 2014. Retrieved January 27, 2011.
- ^ Calaz, R A. An Introduction To Domestic Radio TV And Satellite Reception CAI (2002) pp119
- ^ a b Bains, Geoff. "Getting The Most Out Of An LNB" What Satellite & Digital TV (November, 2008) pp50-51
- ^ "Satellite Glossary". SatUniverse.com. Archived from the original on July 16, 2011. Retrieved January 27, 2011.
- ^ "Ku dish through glass". satelliteguys.us. Archived from the original on April 7, 2014. Retrieved November 6, 2013.
- ^ "Understanding lnb specifications" (PDF). SatCritics Technicals. 2002-11-15. Archived (PDF) from the original on 2012-04-25. Retrieved 2011-11-08.
- ^ "Professional Dish Installation" (PDF). ASTRA (GB) Limited. March 2005. p. 7. Archived from the original (PDF) on 2011-07-16.
- ^ "Astra Glossary - Quattro LNB". SES ASTRA. Archived from the original on July 15, 2011. Retrieved December 30, 2010.
- ^ Bains, Geoff. "Inverto Unicable LNB" What Satellite & Digital TV (February, 2006) pp60-62"
- ^ "Inverto - IDLU-UWT110-CUO1O-32P -". www.inverto.tv. Archived from the original on 2016-08-20. Retrieved 2016-07-01.
- ^ "Unitron catalog" (PDF). Archived (PDF) from the original on 2016-09-19. Retrieved 2016-07-01.
- ^ "Optel". www.optelit.com. Archived from the original on 2016-08-06. Retrieved 2016-07-01.
- ^ popcom.be. "Wideband to Quattro Convertor [sic] - Unitron Group". Unitron Group. Archived from the original on 2016-06-23. Retrieved 2016-07-01.
- ^ "Sky Q Installation" (PDF). Archived from the original (PDF) on 2016-07-05.
- ^ "Archived copy" (PDF). Archived (PDF) from the original on 2015-12-23. Retrieved 2016-05-14.
{{cite web}}
: CS1 maint: archived copy as title (link) - ^ LNB http://www.unitrongroup.com/en/news-events/unitrongroup-introduces-wideband-satellite-product-family.html Archived 2020-08-06 at the Wayback Machine
- ^ "Unitron Group • Your dedicated partner for customize IP and RF solutions". Archived from the original on 2016-08-10. Retrieved 2016-05-14.
- ^ "FibreMDU Optical LNB". Global Invacom. Archived from the original on June 17, 2012. Retrieved January 12, 2010.
- ^ Bains, Geoff. "Multi-feed dishes" What Satellite & Digital TV (August 2007) pp44-47