Our Earth And Satellite System

[sibtain ali]

Our Earth & Satellite System

History:

The first satellite television signal was relayed from Europe to the Telstar satellite over North America in 1962. The first geosynchronous communication satellite, Syncom 2 was launched in 1963. The world's first commercial communication satellite, called Intelsat I (nicknamed Early Bird), was launched into synchronous orbit on April 6, 1965. The first national network of satellite television, called Orbita, was created in Soviet Union in 1967, & was based on the principle of using the highly elliptical Molniya satellite for re-broadcasting and delivering of TV signal to ground downlink stations. The first domestic North American satellite to carry television was Canada’s geostationary Anik 1, which was launched in 1972. ATS-6, the world's first experimental educational and Direct Broadcast Satellite, was launched in 1974. The first Soviet geostationary satellite to carry Direct-To-Home television, called Ekran, was launched in 1976.

Technology Used:

Satellites used for television signals are generally in either highly elliptical (with inclination of +/-63.4 degrees and orbital period of about 12 hours) or geostationary orbit 37,000 km (22,300 miles) above the earth’s equator. U can confurm this statement from the 11th class book of “Physics” chapter number 9 page number “179 to 199” (pages may be change in new edition) there u will also see cetains equations which will help u a lot in understanding this mechanism some portain u can also get from 12th class book. We simply ignore our books if we just read them carefully they will certainly provide us a huge knowledge…
Satellite television, like other communications relayed by satellite, starts with a transmitting antenna located at an uplink facility. Uplink satellite dishes are very large, as much as 9 to 12 meters (30 to 40 feet) in diameter. If u want to see them on TV then u can see these huge dish’s used for uplink purpose in DD Direct+ prmotion when they are advertising their package in background they shows the dish’s used by DD Direct+ for uplink purpose the increased diameter results in more accurate aiming and increased signal strength at the satellite. The uplink dish is pointed toward a specific satellite and the uplinked signals are transmitted within a specific frequency range, so as to be received by one of the transponders tuned to that frequency range aboard that satellite. The transponder 'Retransmits' the signals back to Earth but at a different frequency band (to avoid interference with the uplink signal), typically in the C-band (4–8 GHz) or KU-band (12–18 GHz) or both. The leg of the signal path from the satellite to the receiving Earth station is called the “Downlink”
A typical satellite has up to 32 transponders for Ku-band and up to 24 for a C-band only satellite, or more for hybrid satellites. Typical transponders each have a bandwidth between 27 MHz and 50 MHz. Each geo-stationary C-band satellite needs to be spaced 2 degrees from the next satellite (to avoid interference). For KU the spacing can be 1 degree. This means that there is an upper limit of 360/2 = 180 geostationary C-band satellites and 360/1 = 360 geostationary KU-band satellites. C-band transmission is susceptible to terrestrial interference while KU-band transmission is affected by rain (as water is an excellent absorber of microwaves).

Why Signals become weaker:

The downlinked satellite signal, quite weak after traveling the great distance (see inverse-square law), is collected by a parabolic receiving dish, which reflects the weak signal to the dish’s focal point. Mounted on brackets at the dish's focal point is a device called a feedhorn. This feedhorn is essentially the flared front-end of a section of waveguide that gathers the signals at or near the focal point and 'conducts' them to a probe or pickup connected to a LNB(low-noise block downconverter). The LNB amplifies the relatively 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. The evolution of LNB’s was one of necessity and invention.
The original C-Band satellite TV systems used a “Low Noise Amplifier” connected to the feedhorn at the focal point of the dish. The amplified signal was then fed via very expensive 50 Ohm impedance coaxial cable to an indoor receiver or in other designs fed to a downconverter (a mixer and a voltage tuned oscillator with some filter circuitry) for downconversion to an intermediate frequency. The channel selection was controlled, typically by a voltage tuned oscillator of silver color with the tuning voltage being fed via a separate cable to the headend. But this simple design evolved.
Designs for microstrip based converters for Amateur Radio frequencies were adapted for the 4 GHz C-Band. Central to these designs was concept of block downconversion of a range of frequencies to a lower, and technologically more easily handled block of frequencies (intermediate frequency).
Direct broadcast satellite dishes are fitted with an LNBF, which integrates the feedhorn with the LNB.
The satellite receiver demodulates and converts the signals to the desired form (outputs for television, audio, data, etc.). Sometimes, the receiver includes the capability to unscramble, the receiver is then called an Integrated receiver/decoder or IRD. The cable connecting the receiver to the LNBF or LNB must be of the low loss type RG-6 or RG-10, etc. It cannot be standard RG-59. Now-a-days RG-7 cable is not available in Pakistan as I have seen a friend was asking about that particular cable
(A new form of omnidirectional satellite antenna, which does not use a directed parabolic dish and can be used on a mobile platform such as a vehicle, was recently announced by the University of Waterloo.

Our Earth & our Satelite system:

Most of the people want to know if Earth is rotating then why it won’t happen that @ day time they are watching Intelsat 7/10 which is @ 68.5 & @ night time Thaicom 2/5 located @ 78.5 degree east. This happens because our Earth & the satellite are moving with the same pace. Earth is moving with 11 m/s so the speed of satellite is also the same. These satellites are in-between the pull of Earth & Moon. I mean the force by which Earth is pulling a satellite with the same pace. If our satellite is out of that gap then it will either move towards Earth or towards the Moon. So we have to keep it in-between this gap with the same speed @ which Earth is moving
For more details check this equation presented by “Newton”

F=G M1M2/ (R)2 here G is a constant

The value of “G” is 6.673*(10)-11 N(M)2(Kg)2

[parad0x_i]

A new form of omnidirectional satellite antenna, which does not use a directed parabolic dish and can be used on a mobile platform such as a vehicle, was recently announced by the University of Waterloo

Crossed dipoles laid flat were used many years ago by Radio Amateurs (Hams) to receive satellite signals from Amsat

In fact any flat metal surface or dipole array will receive satellite signals but not with the efficiency of a parabola which is aimed at a particular satellite which then 'collect's a larger amount of signal.. eliminating much of the Earth noise.. and directing the wanted signal towards an LNB