Results 1 to 1 of 1
  1. #1
    Senior Member

    Join Date
    Oct 2010
    Thanked 4,376 Times in 2,255 Posts

    Different Types of LNB's


    Direct broadcast satellite (DBS) dishes use an LNBF (LNB with feedhorn), which integrates the antenna feedhorn with the low noise block converter (LNB). Small diplexers are often used to distribute the resulting IF signal (usually 950 to 1450 MHz) piggybacked in the same coaxial cable jacket which carries lower-frequency terrestrial television from an outdoor antenna. Another diplexer then separates the signals to the receiver of the TV set, and the integrated receiver/decoder (IRD) of the DBS set-top box.

    Newer Ka band systems use additional IF blocks from the LNBF, one of which will cause interference to UHF and cable TV frequencies above 250 MHz, precluding the use of diplexers. The other block is higher than the original, up to 2.5 GHz, requiring the LNB to be connected to high-quality all-copper RG-6/U cables. This is in addition to higher electrical power and electrical current requirements for multiple dual-band LNBFs.

    For some satellite Internet and free-to-air (FTA) signals, a universal LNB (Ku band) is recommended. Most North American DBS signals use circular polarization, instead of linear polarization, therefore requiring a different LNB type for proper reception. In this case, the polarization must be adjusted between clockwise and counterclockwise, rather than horizontal and vertical.

    In the case of DBS, the voltage supplied by the set-top box to the LNB determines the polarization setting. With multi-TV systems, a dual LNB allows both to be selected at once by a switch, which acts as a distribution amplifier. The amplifier then passes the proper signal to each box according to what voltage each has selected. The newest systems may select polarization and which LNBF to use by sending DiSEqC codes instead. The oldest satellite systems actually powered a rotating antenna on the feedhorn, at a time when there was typically only one LNB or LNA on a very large TVRO dish.

    Universal LNB

    A universal LNB can receive both polarisations (Vertical and Horizontal) and the full range of frequencies in the satellite Ku band. Some models can receive both polarisations simultaneously (known as a quattro LNB and used with a multiswitch) through four different connectors Low/Hor, Low/Ver, High/Hor, High/Ver, and others are switchable (using 13 volt for Vertical and 17 or 18 volt for Horizontal) or fully adjustable in their polarisation (this is relatively rare as this requires a separate polarisor, and it's also not part of the Universal LNB specification).

    Here is an example of Universal LNB specifications:

    * LO: 9.75 / 10.6 (or rarely 10.75) GHz (the 10.6 GHz Oscillator is selected by applying a 22 kHz tone to the cable)
    * Freq: 10.7 - 12.75 GHz (slightly wider for 10.75 GHz LOs)
    * NF: 0.7 dB
    * Polarisation: Linear

    Standard North America Ku-band LNB

    By covering a smaller frequency range an LNB with a better noise figure can be produced. Pay TV operators can also supply a single fixed polarization LNBF to save a small amount of expense.

    Here is an example of a standard linear LNB:

    * Local oscillator: 10.75 GHz
    * Frequency: 11.7-13.2 GHz
    * Noise figure: 1 dB typical
    * Polarization: Linear

    North America DBS LNB

    Here is an example of an LNB used for DBS:

    * Local oscillator: 11.25 GHz
    * Frequency: 12.2-12.7 GHz
    * Noise figure: 0.7 dB
    * Polarization: Circular

    C-band LNB

    Here is an example of a North American C-band LNB:

    * Local oscillator: 5.15 GHz
    * Frequency: 3.4-4.2 GHz
    * Noise figure: ranges from 25 to 100 kelvins (uses Kelvin ratings as opposed to dB rating).
    * Polarization: Linear

    Dual/Quad/Octo LNBs

    Two or four or eight LNBs are in one unit to enable use of multiple receivers on one dish. {Note: In the UK, the term "dual" is reserved for LNBs having two feedhorns, such as the Monobloc type. The term "twin-output" is used for an LNB having two independent outputs.}

    Quattro LNBs

    A quattro LNB is a special type of LNB, used in shared installation, using one or more multiswitches to deliver signals to any number of receivers. It has four outputs, but those can not (sensibly) be connected to receivers directly. Instead each of them supplies only 1/4 of the available channels (Lo/Hi band and H/V polarization) to a multiswitch or an array of multiswitches, which then supply individual receivers like a normal LNB output would.

    Note again the difference between a quad (or double twin) and a quattro. A quattro LNB has four independent outputs; each of them has a separate switch for band/polarization. A quad LNB can drive four receivers directly.

    Monoblock LNBs

    A Monoblock LNB (also spelled "monobloc") is a unit consisting of two LNBs and is designed to receive satellites spaced close together, generally 6°. For example in parts of Europe, monoblocks designed to receive the Hot Bird and Astra 19.2°E satellites are popular because they enable reception of both satellites on a single dish without requiring an expensive and noisy rotator. A similar advantage is provided by the Duo LNB for simultaneous reception of signals from both the Astra 23.5°E and Astra 19.2°E positions.

    Cold temperatures

    It is possible for an LNB to physically freeze due to ice build-up in very low temperatures, obscuring the signal. This is only likely to occur when the LNB is not receiving power from the satellite receiver (i.e. no programmes are being watched). To combat this, many satellite receivers provide an option to keep the LNB powered while the receiver is on standby. In fact most LNBs are kept powered because this helps to stabilise the temperature and, thereby, the local oscillator frequency. In the case of UK BSkyB receivers, the LNB remains powered while in standby so that the receiver can receive firmware updates and Electronic Programme Guide updates. In the United States the LNB connected to DishTV receivers remains powered as well as those receivers that receive software and firmware updates and guide information over the air at night.


  2. The Following 6 Users Say Thank You to silverfox0786 For This Useful Post:

    acco (21-12-10),Conaxthewarrior (26-05-12),danishdude (22-03-11),kegrka (10-05-12),proteus4 (06-09-16),Sicilian (21-12-10)

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts