Low-noise block converter

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Working system: CDMA 800 Frequency: Upstream: 790-815MHz Downstream: 835-860MHz Gain: 55-70dBi Output radio frequency: Upstream: 0.5-2W Downstream: 0 - +10Bm Delay time of delivery Noise coefficient Power: 25W Capacity: 8 mobile phones can be used at the same time Coverage range: 100 square meters Payment Details: Payment Terms:




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Ku-band LNB with both sides uncovered.

A low-noise block converter (LNB, for low-noise block, or sometimes LNC, for low-noise converter) is the (receiving, or downlink) antenna of what is commonly called the parabolic (actually paraboloid) satellite dish commonly used for satellite TV reception. It is functionally equivalent to the dipole antenna used for most other TV reception purposes, although it is actually waveguide based. Whereas the dipole antenna is unable to adapt itself to various polarization planes without being rotated, the LNB can be switched electronically between horizontal and vertical polarization reception. The LNB is usually fixed on or in the satellite dish, for the reasons outlined below. The corresponding component in the uplink transmit link is called a Block upconverter (BUC).

Satellites use comparatively high radio frequencies to transmit their signals.



LNBF disassembled (All Parts)

As microwave satellite signals do not easily pass through walls, roofs, or even glass windows, satellite antennas are required to be outdoors, and the signal needs to be passed indoors via cables. When radio signals are sent through coaxial cables, the higher the frequency, the more losses occur in the cable per unit of length. The signals used for satellite are of such high frequency (in the multiple gigahertz range) that special (costly) cable types or waveguides would be required and any significant length of cable leaves very little signal left on the receiving end.

The job of the LNB is to use the superheterodyne principle to take a wide block (or band) of relatively high frequencies, amplify and convert them to similar signals carried at a much lower frequency (called intermediate frequency or IF). These lower frequencies travel through cables with much less attenuation of the signal, so there is much more signal left on the satellite receiver end of the cable. It is also much easier and cheaper to design electronic circuits to operate at these lower frequencies, rather than the very high frequencies of satellite transmission.

The low-noise part means that special electronic engineering techniques are used, that the amplification and mixing takes place before cable attenuation and that the block is free of additional electronics like a power supply or a digital receiver. This all leads to a signal which has less noise (unwanted signals) on the output than would be possible with less stringent engineering. Generally speaking, the higher the frequencies with which an electronic component has to operate, the more critical it is that noise be controlled. If low-noise engineering techniques were not used, the sound and picture of satellite TV would be of very low quality, if it could even be received at all without a much larger dish reflector. The low-noise quality of an LNB is expressed as the noise figure or noise temperature.

For the reception of wideband satellite television carriers, typically 27MHz wide, the accuracy of the frequency of the LNB local oscillator need only be in the order of 500kHz, so low cost dielectric oscillators (DRO) may be used. For the reception of narrow bandwidth carriers or ones using advanced modulation techniques, such as 16-QAM, highly stable and low phase noise LNB local oscillators are required. These use an internal crystal oscillator or an external 10MHz reference from the indoor unit and a phase-locked loop (PLL) oscillator.

Contents

1 LNBFs

2 Universal LNB

3 Standard North America Ku-band LNB

4 North America DBS LNB

5 C-band LNB

6 Dual/Quad/Octo LNBs

7 Monoblock LNBs

8 Cold temperatures

9 See also

10 External links


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LNBFs



Ku-band linear-polarised LNBF

Direct broadcast satellite (DBS) dishes use an LNBF (NB feedhorn), which integrates the antenna feedhorn with the LNB. Small diplexers are often used to distribute the resulting IF signal (usually 950 to 1450 MHz) piggybacked in the same cable TV wire that 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 250MHz, precluding the use of diplexers. The other block is higher than the original, up to 2.5GHz, 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.

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