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The Earth Station
Published in Jerry D. Gibson, The Communications Handbook, 2018
Received satellite signals are extremely low in level at the antenna feed point and require amplification to a level acceptable to be passed on to the satellite receiver or downconvertor. The amplifier must be capable of considerable gain with low noise, and it is usually mounted at the feedhorn to achieve the best results. This portion of the system is referred to as the low-noise amplifier (LNA) or low-noise block down-converter (LNB). Two LNAs or LNBs are required if both polarizations are used on the receive system. The LNA and LNB both use a gallium-arsenide field effect transistor (GAsFET) design to achieve the low-noise performance. The LNA amplifies the incoming receive signal and passes it to the receiver at the original operating frequency. The LNB amplifies the received signal and converts it to an L-band frequency of 950-1450 MHz. Noise performance of an LNA or LNB is measured in degrees Kelvin. Today it is not uncommon to find LNAs or LNBs with noise temperatures of 30° K or better. The gain of the LNA or LNB along with its noise temperature are used when calculating total receive system gain.
Television systems
Published in J. Dunlop, D. G. Smith, Telecommunications Engineering, 2017
The satellite transmission reaches the receiver dish at microwave frequencies (12 GHz for example) and it is necessary to down-convert this frequency to a value suitable for transmission over a coaxial cable to the MAC decoder. The initial amplification and down-conversion to a first IF (usually between 950 MHz and 1.7 GHz) takes place at the point of reception (i.e. at the dish) in a unit known as the low-noise block (LNB). The LNB has a noise figure between 1 dB and 1.6 dB with an overall gain of in the region of 60 dB. The output of the LNB is fed by coaxial cable to a satellite tuner which performs a second down-conversion to an IF of about 480 MHz. The coaxial feeder is also used to supply power to the LNB (typically 200 mA at 15 V). The signal at 480 MHz is then fed to a frequency demodulator and the original luminance and chrominance signals are produced in a MAC decoder. In order to achieve the full potential of MAC transmissions the final output of the decoder can be made available as RGB signals and the majority of modern TV receivers on sale in Europe can accept such signals via a EURO-AV (SCART) socket, which means that such a receiver can accommodate both satellite and terrestrial transmissions.
Content distribution networks
Published in Philip J. Cianci, Technology and Workflows for Multiple Channel Content Distribution, 2012
The power of a radio transmission decreases in proportion to the square of the distance it travels. A weak downlinked signal is reflected by a parabolic receiving dish to a feedhorn at the dish's focal point. This feedhorn is the flared front end of a section of waveguide that “conducts” signals to a probe or pickup connected to a low-noise block (LNB) downconverter. The LNB amplifies the weak signals, filters the block of frequencies in which the satellite TV signals are transmitted, and converts the block of frequencies to a lower frequency range in the L-band range, 950–1450 MHz.
The Changing Face of Public Broadcasting in India
Published in IETE Journal of Education, 2023
The digital satellite TV signal is beamed towards the target area on the Earth, by means of a directional antenna, of the geostationary satellite. The carrier frequencies are in the 10–14 GHz range, and a small parabolic rooftop dish antenna, of 600 mm diameter, is used for receiving the signals (Figure 3). The information is modulated on the carrier using single carrier quadrature phase shift keying (QPSK). A low noise block (LNB), containing antenna feed and low noise mixer, down converts the incoming Ku band signal to an intermediate frequency (IF) in the 950–2150 MHz range. This IF signal connects to the user set top box (STB), by means of a low loss coaxial cable. The STB contains the tuner and IF sections to convert the incoming signal to a lower IF, as well as demodulators/decoders. The IF signal is amplified and demodulated to recover the digital bit stream. The service providers supply proprietary STB, along with subscription control and decoding software.