How Low Noise Block Downconverters Work With Satellite TV

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How Low Noise Block Downconverters Work With Satellite TV

A low-noise block downconverter, commonly called a low-noise block (LNB) for short, is a central component of a satellite dish. Its primary function is to convert incoming signals from a satellite in order for them to be viewed on a television. The LNB rests on the end of the arm on a dish, and receives information from the feed horn. It passes downconverted signals to a decoder, which prepares the images for viewing.

To understand how this process works, it is necessary to consider the frequency satellite signals are transmitted in, how these signals are received by a dish, and the role an LNB plays within the context of other components. The performance and features of LNBs vary from one model to the next, so it is also worth examining the range of products available. Noise figures indicate how much noise is allowed through by the LNB, and gain indicates the signal strength as it is passed through a cable to the TV receiver. Skew and polarisation can also affect a signal quality, while the number of outputs on an LNB determines how many satellite signals can be received simultaneously.

LNBs can be purchased as individual units, and are sold by dish providers and online retailers like those on eBay. Buyers looking for a replacement LNB can find several models available, some of which can enhance the performance of a dish. Learn about the role of an LNB, and consider its features and performance to understand how it works with satellite TV.

About Satellite Dishes

To understand how an LNB functions, it is useful to be familiar with the basic parts related to a dish. The following table offers brief descriptions of these components.



Low-Noise Block Converter (LNB)

Rests on the end of the dish’s arm. Converts incoming satellite signals so they may be read by the TV receiver.

Coaxial Cable

Connects the LNB to a TV receiver.

Feed Horn

Adjacent to the LNB on the dish’s arm. Receives incoming signals and passes them to the LNB for conversion.


Accepts converted signals from the LNB and sends them to the TV receiver.

Parabolic Reflector

The physical dish. May be circular or oval. Bounces signals from a satellite back to a concentrated point at the end of its arm, where the LNB and feed horn are located.


A pair of LNBs that allows reception from two different satellites. Only one LNB may be active at any time, and users must switch between the two. Contains one output.

Multi-Port LNB

Multiple LNBs with multiple outputs. Enables simultaneous reception of two or more satellite signals.


Separates a signal from a single output and allows it to be routed into multiple rooms of a home.

Keep in mind that these parts can vary from one dish to the next. Many components, such as the LNB, can be designed in several different styles.
Role of an LNB
Satellites must transmit their signals in very high frequencies to reach dishes on Earth. These frequencies cannot be handled by standard cables or receivers within a home, and must undergo several steps to produce a visible picture on the television. A satellite sends its signals in groups, called blocks. These are collected by the feed horn on a dish, and passed to the LNB, where they are converted. For example, an incoming signal sent at 3 GHz, or 3000 MHz is converted by the LNB to something closer to 1000 MHz.

The signal initially passes through a filter circuit in the LNB, which eliminates unwanted noise. It is then sent to an amplifier that enhances the desired signal and sends it to a mixer circuit, which performs the actual downconversion. The mixer selects the correct combination of signals created during the downconversion and passes it to the decoder, which prepares them for the TV receiver.


Decoders work closely with an LNB, and complete the block conversion process. The decoder calculates the frequency needed for a visible picture, and chooses between the two polarities of incoming signals: vertical or horizontal. Signals received on one polarity interfere little or not at all with the other, which allows more channels to be received. The decoder chooses the necessary one for each programme. It also provides power to the LNB, which is sent via the coaxial cable. As the decoder receives its signal, it is also sending the power needed to operate the LNB.

LNB Performance

The performance of an LNB can vary from one product to the next, and units are designed with different capabilities. For example, the amount of noise the LNB eliminates is different for each product. The gain of an LNB is also important, as it affects how strongly the signal is transmitted through the coaxial cable. Learn about noise figures, gain, skew, and output connections to understand the additional roles an LNB plays.

Noise Figures

Noise figures refer to the amount of unwanted noise an LNB lets through, and are measured in decibels (dB). Lower numbers indicate less noise, and are therefore more desirable. Units capable of reducing noise to 0.9 dB or less are ideal. Be aware, however, that listed noise figures on a product may not reflect actual performance. Due to discrepancies in production and testing conditions, two products listed at the same noise figure may perform at different levels. However, changes in noise figures under 1.0 dB are difficult or impossible for human ears to detect.


Gain measures signal strength during transmission through a coaxial cable. High levels of gain can send a signal further along a cable, though products with a high gain may not function properly with a short cable.

Skew and Polarisation

To properly read signals from a satellite, an LNB must be in the proper position and have its skew set correctly. Most dishes have some type of read-out that indicates signal quality, which is shifted by adjustments to the LNB’s skew. Poor alignment of the LNB can also result in uneven reception of the vertical and horizontal polarities, and some products are better than others at separating the two. This ability is indicated by an LNB’s cross polar rejection.


LNBs can have multiple outputs, and this determines the number of satellite signals that can be received simultaneously. They may have one, two, four, or eight outputs. Most modern dishes are designed with multiple outputs, though it is also possible to purchase a monobloc. This allows reception of multiple signals, but users may only use one at a time.

How to Buy Low-Noise Block Downconverters on eBay

A high number of LNBs can be purchased on eBay. To shop for these products, you may enter keywords into the search field on the homepage. For example, to see an LNB with four outputs, type "quad LNB" into the search field. Search results can be narrowed by adding new keywords on any page. It is also possible to search using eBay's category options. Look for these links to browse by item type, price, condition, and more. A combination of keywords and category links is often the best way to locate specific items on the site.

Research individual listings once you have located the type of LNB you'd like. Click on the name or image of an item in search results to see information about shipping charges, shipping methods, and the forms of payment accepted by the seller. Read the item description provided, and compare it with available photos to be clear on the product being sold. Contact the seller if you have any questions.

Take a moment to investigate eBay sellers to ensure a favourable buying experience. Look for a positive feedback rating and number of completed transactions in an item listing to judge a user's experience and reliability. If you'd like more detailed information, click on the seller's name. Full profiles reveal comments and ratings left by previous buyers about a seller's performance. Once you have received your LNB, return to eBay to leave feedback about your experience.


Low-noise block downconverters are a central component of satellite dishes. They are responsible for downconverting the relatively high frequencies of incoming signals so they may be displayed on a television screen. LNBs receive information from the feedhorn, and transmit the converted signal to the decoder. In this process, LNBs must also reduce unwanted noise, which is done by a filter circuit. Ideally, LNBs reduce noise to less than 1.0 dB. The signal is then sent to a mixer, which performs the actual downconversion, and selects the appropriate combination of signals for the decoder.

LNBs are produced with varying levels of performance. Consider noise figures, gain, and the accuracy of a unit's skew and polarisation. The number of outputs on a unit determines how many satellite signals can be received simultaneously. LNBs are created with as many as eight outputs.

LNBs can be purchased from satellite dish providers and online retailers. Marketplaces like eBay have listings for many types of LNBs, and can be used to easily compare prices and products. Understand the role of an LNB and the features available to find products that can enhance the picture quality and performance of satellite TV.

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