Low-noise block downconverter

As low noise signal converter ( from the English Low Noise Block, short LNB, and Low Noise Converter LNC short ) refers to the first, located at the focal point of a parabolic antenna electronic assembly of a satellite receiving system.

It implements the satellite frequency from 10.7 to 11.75 or 11.8 to 12.75 GHz, for example, to the range 950-2150 MHz, thereby allowing the cable transmission through a coaxial cable and recently also with optical waveguides and reception with a satellite receiver. A " digital compatible " universal LNB must not process digital signals, but only be able to implement the full frequency range from 10.7 to 12.75 GHz. Initially digital DVB signals are sent only in the upper range from 11.7 GHz, in view of the analog TV switch-off almost all transponders from 10.7 GHz are now upwards but occupied with digital TV signals.

An LNB consists of a combination of a low noise amplifier ( LNA) with a block converter ( see below). Is there a feed horn mounted ( from the English feedhorn for " feed horn " ), it is also called LNBF ( Low Noise Block Feed ) or UAA (Low Noise Feed ) refers.

Design and function

After the high-frequency microwaves from a geostationary telecommunications satellites were focused by a parabolic mirror, the LNB following additional tasks fulfilled with the satellite reception:

Power to the LNB by means of remote power supply via the antenna cable. The since the late 1980s, Marconi established standard allows a selection of the plane of polarization of the amount of the supply voltage ( 14 V vertical, horizontal 18 volts ). The switching threshold is set at 15 V and allowed voltage drops up to 3 diodes in upstream DiSEqC switches and the power cable itself when universal LNB ( 10.7-12.75 GHz) can with a superimposed constant switching frequency (22 kHz ± 20 % ) alternatively added later high Band can be selected from 11.7 GHz. In order to use more than two switching criteria operate in the early 1990s jointly by the satellite operator Eutelsat and Philips digital control bus DiSEqC - later with rear channel speaker - developed. This allows with a modulated 22 kHz frequency control up to 256 different components of a satellite receiving system. DiSEqC components can operate at a reduced operating voltage of 12 volts to reduce power dissipation.

The entire functional unit is normally integrated into a common weatherproof housing. In addition to protecting against moisture, dust, and temperature effects, it must ensure that the area of ​​the shaft entrance window and outside if possible, no impurities or water ( optionally also as snow or ice) can adhere.

Problem areas of satellite reception

Considering the transmission lobe of a satellite, in other words its illumination zone on the earth's surface ( in English called footprint ), it is understood that the signal power density at the bottom can only be slight. Thus, the useful signal from the thermal noise of the cosmic background radiation to the entire baseband related at all lifts out, parabolic mirror can be used. These are derived in the correct orientation on the geostationary satellite sufficient amount of useful signal and little interference to the " feed" of the LNB. With too low signal to noise ratio (SNR, english signal - to-noise ratio called ) as it can by too small or misaligned parabolic mirror, through attenuation of the signal ( snow, rain ) or by injecting additional noise sources (reflections ) coming, is not reception possible.

Since the noise power of the thermal noise is dependent on the base-band width, which is the more problematic, the greater the used frequency range.

For a universal LNB is switched between two different frequency ranges to cover the whole frequency range of 10.7-12.75 GHz, since the frequency bandwidth between upper and lower cut-off frequency (2.05 GHz ) is not in the coverage area of the satellite receiver from 950 - 2150 MHz fits.

Since each amplifier roars and this inherent noise adds to the signal, the SNR can never be better, but only worse in a signal chain. Therefore, a LNB requires a particularly low noise throughout the baseband amplifier to allow reception is poor or reception. Typical of universal LNBs is since 2004 a self-noise ( related terms: noise, noise figure, Eng noise figure, noise floor. ) Of about 0.6 dB ( 0.6-0.7 dB at 21 ° C are considered to be very good). Lower noise figures of 0.2 and 0.3 dB are not possible in the consumer sector, as in the first stage of the LNA already has, according to the manufacturer's data sheets of the transistor gain under optimal conditions, a noise level of about 0.3 dB. This means that the total noise can be only greater when a plurality of amplifier stages are connected in series ( with the so-called low-noise HEMTs ). In this case, the gain of each stage is crucial.

In the selection of receiver components for weather resistance should be taken into account. In addition to general air pollution and snow and ice, bird droppings can dampen the signal ( receiving side feedhorn ). Occasionally LNBs available with a thin film cover to achieve a even lower attenuation value. However, these are very delicate and difficult to clean.

Origin of the name

A low self-noise is indeed an important quality characteristic of this component, " Low Noise " as part of their name, however, is quite peculiar and can only be explained by the historical development.

In the early days of satellite reception ( and for special applications even today ) the high frequency signal was only amplified by the satellite and routed to an intermediate frequency to the receiver without implementation. Here, a low noise was particularly important and the corresponding time very elaborate high-frequency amplifiers were LNA (low noise amplifier ) called. With this construction, only a short, low-loss cable connections between antenna and receiver are possible.

To enable satellite reception even for homes, was introduced in the 1980s, the LNC (low noise converter ). Here in addition to the amplification reaction also takes place to a lower intermediate frequency (IF ), which simplifies the connection to the receiver. Receive frequency range of 10.95 to 11.7 GHz LNC was normally; for TV - SAT and TDF satellites were LNC with the reception frequency range from 11.7 to 12.5 GHz.

• To receive more polarization planes either an upstream or a polarizer in an LNC arranged in the waveguide polarization filter with then own for each polarization LNC was necessary.
• To receive two different satellite frequency bands, as first used by the German Telecommunications Satellite DFS Copernicus in broadcasting DTH, LNC were necessary, can receive two frequency bands. DFS Copernicus sent in the frequency range from 10.95 to 11.7 and 12.5 to 12.75 GHz.

Since the early 1990s LNB is used in the private sector that can receive both polarities. The supplemental block refers to that of a multiple LNB frequency blocks of different polarization and frequency are processed at once;

• Either they are issued in parallel on separate IF signal outputs
• Or select the receiver by means of control signals to an LNB for receiving a desired frequency block.

LNCs are therefore only to be found in existing plants and in professional antenna systems today and will not be re-installed in the direct reception.

With complete integration of the components it is sometimes called the LNBF or from the LNF. " Feed " means receive the signal feed.

The different abbreviations are used but often used interchangeably in practice by experts.

Designs

Only with the advent of DTH (Direct to Home) antennas (Astra was there one of the pioneers ), the feed horns are mounted directly on the Ku band LNBs. Prior to the LNB had a standardized flange fitted on the flange of the feed horn. That was also the extent necessary, as the LNBs knew neither one nor a level switch low / high- band - switching in the early years. The plane separation was with so-called Ortho mode - made ​​or polarizers - this was then per level, a separate LNC necessary. LNBs are often used together in receiving systems with the so-called multi-switches.

• Single or twin LNB with an output for direct connection to a receiver.
• Twin or double LNB with two independent outputs to connect two receivers. The corresponding switching device ( multi-switch ) is usually integrated. But there are also (older) versions so-called dual- LNB for the pure low-band reception with various terminations, the fixed each horizontal and vertical polarization deliver (for connection to an external multi-switch ).
• Quad or Quattro Switch LNB with 4 independent ports to connect 4 receivers. The multi-switch is integrated there.
• Quattro - LNB with 4 different connectors (also with Note: Suitability for feed system ). In this variant without built-in multi-switch horizontally and vertically polarized signals are brought out separately for low band and high band. Via a downstream multi-switch then a distribution to virtually any number of satellite receivers carried (up to several hundred).
• Octo LNB with built-in multi-switch for direct connection of up to eight satellite receivers.
• DUO LNB or monoblock LNB: Here 2 adjacent satellite positions can be received simultaneously with a wide LNB head. Previously often called strabismus LNB. A multi-switch, often for multiple outputs, is already integrated. The LNB is set to the same time the satellite Astra 19.2 ° East and Hotbird 13 ° East or Astra 23.5 ° East can receive. The two satellite positions are controlled by tone burst or DiSEqC.

• Unicable LNB has a single port that these multiple receivers can be connected on a common coaxial cable. A unicable LNB is not as usual a complete frequency band, but only for each connectable receiver on UB ( = User Band ) ( "UB slot ID" and " UB- frequency " ) from. The program selection is made in the LNB for each receiver separately via DiSEqC - controlled commands. The output frequency of the LNB does not change. A unicable LNB can usually up to four satellite receivers with signal supply, some manufacturers allow you to connect up to 16 receivers, but that is not standardized and suitable for this purpose receivers are proprietary. There are in addition to the pure unicable LNBs also which from 1 to 3 so-called legacy outputs, where unicable -capable receiver can not be connected.

For the two 4-way types so far no single name has prevailed, which can lead to misunderstandings.

• ILNB ( " interactive LNB" ): If you recently with return channel used in satellite systems, mainly to send and receive Internet signals. Depending on the design it can in Ku- or Ka-band satellites to send and receive from him.

Monoblock LNB

A so-called monoblock summarizes two LNBs for two different satellite positions in a housing. The satellite positions are determined by the LNB housing and the size of the dish. In addition, a DiSEqC relay is installed. This makes it possible to switch between the two positions by means of the DiSEqC satellite signal.

Location

The designs described above are related to the usual satellite television systems in Germany, all of whom work in the Ku- band. However, there are a variety of other LNBs for different frequency ranges and applications, such as Meteosat- LNBs, L-band LNBs, S-band LNB, C-band LNBs.