Feb 20, 2013

LNB function Satellite and Dish Antenna


What is LNB, in the field of Satellite and Dish

Dealing with the problems of weak satellite signals. So we need a parabolic antenna to focus the signal and an LNB (low noise block), or LNBF, universal LNB or feedhorn mounted at the focal point to collect them. However, what is really going on in this small component?

LNB is the heart of the satellite antenna. Basically, it's a cavity resonator which receives satellite signals reflected from the antenna focus and process the signals. Similar to the pipe organ that converts the energy into an electrical signal transmissions. An electronic switch is added to amplify the signal before it is sent to the coax cable and turn it into a lower frequency to reduce signal loss in the cable.

Although descriptions may sound there are major differences between each model, LNB types used today use the same technology, the key differentiating factor is the noise figure has been reduced to the lowest possible value in theory of 0.3 dB in most models. Universal LNB is used to divide the Ku band - which is commonly used in Europe - into two frequency ranges.

Each LNB can only be used for single frequency band, for the S, C and Ku bands each require different cavity resonators. There is also the type to linear and circular signals, which are distinguished by laying the internal dipole.

The power supply for the electronic switch exciting. Power is provided by the receiver and routed via the coax cable. So that is not coax cable only transmits the signal received from the antenna to the receiver, but also requires operating power from the receiver to the LNB (with additional control signals).

Features Switch When change channels
Transponders have one or two different polarization (horizontal / vertical and circular left / right). So the receiver to tell the LNB polarization for a given signal, so that the corresponding dipole can be activated. Voltage power supply as follows: 14 V enable vertical polarization, while 18 V enable horizontal polarization. Although the DiSEqC control device has been developed as a reliable with more than 256 orders, still not used to transfer polarization.

Universal LNB has a second switch mode for extended Ku band. Since the frequency range of the satellite receiver is not wide enough, the frequency range should be separated into two frequency ranges. Switching between the two ranges is controlled by a 22 kHz signal is also sent by the receiver to the LNB when selecting a particular channel. 22 kHz signal is also used for the carrier frequency for DiSEqC control commands in a more complex system configurations. DiSEqC commands can control the multiswitch and the antenna motor.

Various Designs
There are several types of designs for different uses. The following table summarizes the common type of LNB for extended Ku band and show how it is used:

Single LNB suitable for individual acceptance. Acceptance of the principle of a single LNB also included antenna (flat). If the receiver are DiSEqC 1.2 and provides the commands needed to control a motorized dish, single LNB dish combined with motor allows it to receive signals from a satellite. It is a stable configuration, but requires a waiting time until the antenna is moved to the right position when selecting channels from different satellites.

Other designs are only suitable for fixed antenna. LNB twin, quad and octo is to support two, four or eight receivers. Each receiver is connected to the LNB with a separate coax cable, allowing signals to be received separately by each receiver.

Quattro LNB to switch to channel output configuration of four signals (horizontal / vertical and low band / high) simultaneously and is not suitable to be connected directly to the receiver. Its output signal is connected to the switch matrix. With the help of channel matrix and reinforcing making it possible to connect a receiver to this system.

Multifeed for professionals
Multifeed means receiving signals from several satellites simultaneously with one antenna fixed. The advantage of this method is switching between satellites very fast. However, some shortcomings with respect to the acceptance or boundary multifeed are:

Efisiensidalampenerimaan decline to require a larger dish. Can not select more than four satellites. Orbital span of no more than + / - 10 degrees (less rather than more). Satellite distance at least 3 degrees. DiSEqC commands needed to move the signal. If more than one receiver to be connected, then the required Skybox sinyal. Just little Difficult to set the direction of the antenna.

Practical monoblock LNB
Dual LNB is the simplest solution to get reception from two satellites multifeed. This design consists of two separate LNBs in a single tube. The two LNBs can be automatically selected by DiSEqC 1.1 receiver. However, it is only available for satellites with a fixed 3-degree spacing or 6-degrees. In Europe, for example, there LNB monoblock single, twin and quad for the Ku band, with a predetermined distance of 6 degrees (eg for NSS6/Astra or Asiasat3/Asiasat5).


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