24 Jan 2016

Understanding Satellite Signal Transmission:

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A satellite dish system is a sophisticated way of watching television. The signal originates with a satellite above the earth’s atmosphere. That signal must travel a long way to a satellite dish, which has a device that collects the signal bouncing off the dish and sends it to a receiver inside a home. That receiver is connected to a television, on which the user views the signal. This is a simplified explanation. It is necessary to process the signal before transmitting it from the dish to the receiver and the signal goes through some big changes in this process. The device responsible for this is the LNB, which stands for low-noise block down-converter. This is one of the most important parts of a satellite television system as it plays a significant role in determining the quality of the satellite signal. Learning how the correct LNB can help viewers achieve a better satellite signal, as well as learning the basic principles of LNBs, the consumer can choose the right product for his needs. Further, learning how to set it up with the satellite dish and adjust it properly can help the consumer enjoy years of improved signals.

Understanding The LNBs(low-noise block down-converter)

An LNB is a crucial component in delivering a satellite signal to a television. Understanding basic information about LNBs helps users grasp how to achieve an improved satellite signal. This heading details the parts found in an LNB and describes how an LNB works.

Parts of an LNB

The table below lists the parts found in an LNB and the role these parts play in processing a satellite signal so it can transmit to a satellite receiver for viewing on a television.


Part

Role

Low-Noise Amplifier
Amplifies weak satellite dish signal
Keeps additional noise to a minimum
Local Oscillator
Creates new signal within the LNB
Mixes signal the satellite dish receives
Passes signal to the LNB
Frequency Mixer
Mixes satellite dish signal with the local oscillator signal
Lower frequency signal is passed to another amplifier
Intermediate Frequency Amplifier
Amplifies the intermediate frequency signal
Sends it via coaxial cable output(s) to the satellite receiver(s) inside the house
Feedhorn
Collects the satellite signal from the dish and directs it to the LNB
Polariser
Chooses between vertical and horizontal polarised satellite signals

The table above describes the role of the parts found in an LNB. An LNB that includes a feedhorn and polariser may also be known as an LNBF, an LNB-feed, an LNB-feedhorn, or an Astra LNB.

 How an LNB Works

Here follows a more complete description of how these parts work in conjunction with one another and why an LNB is so important in a satellite television system. The image that appears on a television connected to a satellite system starts as a signal from a satellite in space. In order for this satellite signal to reach the satellite dish, it must travel a long way and it therefore has a frequency similar to the waves in a microwave.

This high frequency signal is weak and unsuitable for traveling across a coaxial cable to the satellite receiver to which a television is connected. It is possible to process this signal for viewing on the television without significantly modifying it, but the equipment would be more complex and expensive than the coaxial cable and receiver system satellite television companies use.

In order to maintain a less expensive system of delivering a satellite television signal to a television, an LNB processes the signal to make it suitable for travel across a coaxial cable to a receiver. The LNB starts by using the freehorn to collect into a single signal the numerous microwaves from the satellite that hit the satellite dish. It then amplifies this weak signal, creates a new signal with its oscillator, and mixes the new signal with the satellite signal. One signal has a frequency that is the sum of the two signals and the other signal has a frequency that is the difference. This is an intermediate frequency, suitable for passing through a coaxial cable. The LNB filters out the high frequency signal and passes the intermediate one to an amplifier, which strengthens the signal before passing it from the LNB to a satellite receiver via coaxial cable.

How to Choose the Right LNB

One important aspect of achieving an excellent satellite signal is choosing the right LNB to go with a satellite dish. While the signal may only be as good as the dish is capable of delivering, the right LNB helps ensure that no signal quality is lost when processing the signal and sending it to a satellite receiver. This section provides advice on how to choose the right LNB by considering a few key features and being aware of the different types of LNBs.

LNB Features

When deciding which LNB to purchase, it helps to pay attention to its noise, gain, cross polar rejection, and microphonics resistance.

Noise:    Noise degrades the quality of a satellite signal, resulting in poor reception on the television screen. Unfortunately, increased noise accompanies the amplification of any type of signal. A good LNB produces a minimum of noise, with anything under 0.6 decibels resulting in good reception. The human eye cannot discern the difference between a signal that has 0.6 decibels and 0.1 decibels of noise, so as long as the LNB manufacturer guarantees no more than 0.6 decibels, the LNB should be fine.

Gain:     The gain is how much the LNB strengthens the satellite signal and this is also measured in decibels. It is usually by the dozens of decibels, with a stronger signal likely to result in a clearer picture. A gain can be too high relative to the length of the coaxial cable, though, and this could overload the receiver’s tuner. It is important to note that many manufacturers measure gain at room temperature, so a satellite receiver should continue to deliver power to a LNB when the receiver is in standby mode. Consequently, the LNB does not become cold.

Cross Polar Rejection Many LNBs can switch between the vertical and horizontal polarised signals satellites send, but these signals can interfere with one another. An LNB can prevent this interference through cross polar rejection (CPR), another parameter that is measured in decibels. Areas on the edge of satellite signal reception generally have one type of polarised signal that is stronger than the other, so CPR is important in such areas. The smaller the dish, the less likely it is that signals interfere with one another. A dish diameter of about 1.8 metres is the threshold under which CPR is not a factor.

Microphonics Resistance: Microphonics are the signal disturbances that wind, rain, and hail cause when they come into contact with an LNB. These weather events affect the flow of electrical current through the LNB and this is reflected in signal disturbances that are viewable on the television screen. In many cases, heavy rain and strong wind often prevent the receiver from receiving a signal at all. It is therefore advisable to consult a seller as to the microphonics resistance of an LNB. Even if there is no rating for this feature, a seller may still be able to provide helpful information towards making a buying decision.

LNB Types:   There are a few types of LNBs to meet different standards around the world, but UK satellite owners usually find that their LNBs are, in fact, 

Universal LNBs. Also known as Astra LNBs, they have two modes of operation, one in which they process low band reception of 10.70-11.70 GHz and one in which they process a high band reception of 11.70-12.75 GHz. These are the frequencies of the satellite signals, with the processed intermediate signals registering in the range of 950-1950 MHz and 1100-2150 MHz, respectively.

LNBs may also feature numerous coaxial outputs to send signals to various satellite receivers around a house. Those with two outlets are called twin LNBs, those with four, quad LNBs, and those with eight outlets are called octo LNBs. A quattro LNB has four outlets with each outlet responsible for delivering a quarter of the various channels available. Each outlet sends a signal to a multi switch device, which then distributes the requested signal to each receiver in a building.

How to Position and Tweak an LNB

Choosing the right LNB is only part of the process of maximizing satellite signal performance. Another important aspect is positioning and tweaking the LNB. This section describes how to set up an LNB on a satellite dish and how to skew it for the best possible signal transfer.

Setting Up an LNB

An LNB attached to an arm and the feedhorn must be positioned so that it can pick up waves from every part of the satellite dish. It should not align with any area on the satellite dish because it generally picks up noise from whatever object is in its reception area. Conversely, if it does not line up with the whole surface area of the dish, it cannot pick up a signal from whatever area is outside of the alignment area. The precision this alignment requires means it is often best left to professionals to perform.

Skewing an LNB

Skew refers to the rotational position of the LNB with regards to the satellite dish. Having the position within the correct parameters ensures no errors in data transmission. Accuracy is less important in high-reception areas, but it is highly important in low-reception areas. Adjusting the skew is often a two-person operation if a professional does not perform it. One person loosens the screw or nut fixing the LNB in place and rotates it clockwise, while the other person observes the television and reports on the reception. Some LNBs use pre-fixed settings, making it easy to change the skew by simply changing the setting. As long as the signal quality is at least 50 per cent, the satellite signal should come through clearly in inclement weather.

Conclusion

An LNB is a sophisticated device that processes a weak, extraordinarily high-frequency satellite signal into strong, intermediate-frequency signal a coaxial cable is capable of delivering to a receiver. Because it processes a satellite signal, an LNB is responsible for the quality and strength of that signal and, therefore, how clear the picture appears on the connected television. This guide has explained in depth how LNBs work and how to choose the right one for a satellite television system. It has also provided advice on how to set up an LNB on a satellite dish and how to adjust its rotational angle to ensure the best reception. following the information in this guide, readers should be able to successfully purchase the right LNB and receive great satellite reception on their televisions.
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