This question appears in Mumbai University > Satellite Communication and Network subject

Marks: 10 M

Year: Dec 2014

polarization interleaving

1. Polarization refers to the orientation of the electric vector of the electromagnetic wave in space.
2. Consider the situation where a geostationary satellite is transmitting a linear polarized wave. In the situation the usual definition of horizontal polarization is where the electric field vector is parallel to the equatorial plane and vertical polarization is where the electric field vector is parallel to the earth’s polar axis
3. It will be seen that the sub satellite point on the equator, both polarization will result in electric fields that are parallel to the local horizontal plane. Care must be taken therefore not the use “horizontal” as defined for terrestrial system.
4. For other points on the earth’s surface within the footprint of the satellite beam, the polarization vector (the unit vector in the direction of the electric field) will be at some angle relative to the reference plane. This reference plane will be taken to be that which contains the direction of propagation and the local gravity direction.

Indoor receiving unit of satellite TV/FM receiving

1. In terms of the number of earth station ,the television receive-only(TVRO) and direct broadcaster terminal is likely to remain the most common .there are two general two layout of DBS earth station .there are two units the outdoor unit which mount in the antenna feed and the indoor unit which is fed by coaxial cable from ODU and contain the interface to domestic VHF/UHF TV receiver
2. A high gain GaAs FET amplifier is commonly used for Rf section of receiver; mounted immediately behind the fed to minimize waveguide losses. Image enhancement mixer with noise temperature down to 340 K have been develop for DBS service and may offer lower cost ODU than FET amplifier system which also require a mixtures.
3. A fixed frequency Gunn diode local oscillator is normally used with frequency around 11 GHz. this gives a first IF around 1.2 GHz for the 12 GHz DBS band. The 11 GHz LO is in the ODU, which sends the 1.2 GHZ IF signal to IDU for down conversion to 70Mhz .selection of channel frequency is achieve with a second local oscillator at 1.1 GHz to obtain a 70 MHz IF signal with 30 MHz bandwidth.
4. Further processing of 70 MHz IF signal allows separation of FM sound carrier, which is transmitted separately from the FM video signal. A threshold extension demodulator is used to extract the video signal .the threshold is at approximately 7.5 db in demodulator developed especially for DBS and TVRO use, a significantly lower value than in conventional FM demodulators
5. After demodulation ,video and sound signals are demodulated onto a VHF or UHF carrier using vestigial side band AM for video and FM for sound to produce a combine signal compatible with domestic TV receivers.