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Duo LNB

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A twin-output Duo LNB fitted to a 60cm dish (only one output is connected)

A Duo LNB is a double low noise block-downconverter (LNB) developed by SES Astra for the simultaneous reception of satellite television signals from both the Astra 23.5°E and Astra 19.2°E satellite positions.

It is a monoblock LNB, which comprises two feedhorns with a single body of electronics containing the LNB stages along with switching circuitry to select which received signal is passed to the output(s).

Availability

A Duo LNB can be purchased in most parts of Europe but it is particularly marketed to Germany, the Netherlands, Belgium and the Czech and Slovak Republics.[1]

Duo LNBs operate as universal LNBs and are manufactured under various brand names, such as Maximum and Inverto, in single, twin-output and quad-output versions – with one, two and four outputs (independently selectable for polarity and frequency band), respectively, for one, two or four receivers/tuners.[2]

Background

The Astra 23.5°E orbital position was established as a major source of direct-to-home (DTH) broadcasts for central and western Europe with the launch of Astra 3A at the end of 2007,[3] and some channels moved there from other satellite positions (in particular 19.2° east) so viewers, who were unable to erect two dishes to receive transmissions from both positions, had to choose between them.

In particular, the Czech CS Link and Slovak SkyLink networks moved to Astra 23.5°E, and the Dutch Canal Digitaal launched a new thematic bouquet at 23.5° east in October 2007.[3] The Dutch regional broadcasters all moved to Astra 23.5°E in September 2007, to be lost to viewers without access to the new satellite position.[4]

The Duo LNB was introduced to enable a single satellite dish to be used to receive all the channels from 19.2° east and 23.5° east.

The ASTRA2Connect satellite internet service also operates from 23.5° east and SES Astra plans to launch a further satellite, Astra 3B, to this position before the end of 2009.[3]

Technology

The basic technology behind the Duo LNB is not new. It takes advantage of the fact that signals hitting a dish off-axis will be focused (albeit with some diffusion) off axis in the opposite direction. So, with the dish aligned so that the central LNB is receiving one satellite, a secondary offset LNB can be aligned on the focus of a second satellite spaced away from the first.

This effect has been exploited for many years to receive signals from two satellites at once with a single dish, and two LNBs have been most commonly arranged on a dish in this way for reception of Astra 19.2°E and the Hot Bird satellites at 13° east, primarily for the abundance of TV channels from 19.2° east, and some additional channels (especially adult channels) from 13° east.

A monoblock LNB provide a convenient alternative to fixing and aligning two LNBs to a dish independently. The two feedhorns are positioned at the correct spacing for reception from the two satellites required and the DiSEqC switching system is used to select between the signals from the two satellites with commands from the connected receiver. In other respects, the monoblock LNB acts as a normal LNB to the connected receiver.

The required separation of the monoblock’s feedhorns depends on the angular separation of the satellites to be received, the position of the receive site on the Earth’s surface and the focal length of the dish. Fortunately, monoblock LNBs can be standardised for sites across Europe provided that a “standard” offset dish with a focal length/diameter (f/D) ratio of 0.6 is used.[5]

Monoblock LNBs for 19.2° east and 13° east have been widely available for several years (indeed, the DiSEqC switching system was originally designed for just this setup). However, these do not function correctly for Astra 23.5°E and Astra19.2°E because these satellites are at a different angular separation.

In fact, it can be difficult to physically fit two separate LNBs onto a dish at the correct separation for Astra 23.5°E and Astra19.2°E because their bulk may prevent the feedhorns sitting close enough together.

The Duo LNB is carefully designed with the correct spacing of the feedhorns, DiSEqC level 1.0 switching between the satellites and a low noise amplifier and conversion system.

Name Confusion

The Duo LNB is a monoblock type LNB designed for accessing two satellite positions with a single dish and it should not be confused with a “dual LNB”, which is the common (US) name for an LNB with a single feedhorn but two separate outputs.

A double LNB called just a “Monoblock” will usually be for reception of 19.2° east and 13° east, and not a Duo LNB suitable for Astra 23.5°E and Astra 19.2°E.

See also

References

  1. ^ SES ASTRA “Duo LNB” (August, 2008). Company factsheet
  2. ^ "Monoblock LNBs". www.satontvangst.nl. Retrieved October 21, 2008.
  3. ^ a b c "SES ASTRA Develops Orbital Hot Spot For Broadcasting" (Press release). SES ASTRA. October 23, 2007.
  4. ^ "Digitale Televisie via de Satelliet". Canal Digitaal. Retrieved October 20, 2008.
  5. ^ Bains, Geoff. "ABC Guide To Multi-feed Dishes" What Satellite & Digital TV (August, 2007) 44-47"
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