26-04-2012, 11:53 AM
Satellite Radio
Jan2002p47-52.pdf (Size: 58.18 KB / Downloads: 75)
Introduction
Man has always been fascinated by the ‘heavenly voices’ from
the skies. This fascination has manifested itself in many mythologies
where he has received divine messages, warnings, and
forecasts from the heavens. It was this undiminished fascination
that kept him working towards the radio system. It was one
hundred years ago that Marconi first transmitted the letter ‘S’
across the Atlantic Ocean. At that time, conveying information
across such large distances was not as much a novelty as the new
concept of broadcasting. While telegraphy was constrained by
physical network of lines, radio reached a widespread, unidentified
audience.
Satellite Orbits
A satellite’s orbit is decided depending on the application. The
geo-stationary orbit (GSO) is considered ideal for broadcast
purposes. It is advantageous because of the ease of tracking – or
rather the lack of tracking. In GSO, even though a satellite
moves at a speed of over 10,000 km per hour, it appears to hang
perfectly motionless in the sky.
Modulation
Modulation is the way information is imparted to the electromagnetic
signal that is referred to as the carrier wave. In
amplitude modulation (AM), the amplitude of the radio frequency
(RF) carrier is made to vary in accordance with the audio
waveform. It is obvious that in this mode, it would be quite
sensitive to additive electrical noise. Frequency modulation
FM has a much better noise immunity, as it is the frequency of
the carrier wave that is varied in a small range according to the
audio waveform. However, noise free reception does not necessarily
mean high fidelity (HiFi).
Digital Radio
Because of the tremendous advancement in digital technology
in the recent years satellite radio is fully digital. In a digital
radio, the transmitter processes sounds into patterns of binary
digits and at the listening end, the digital radio reproduces the
sound from the digits. By using techniques of forward error
control, it is possible to make the reception virtually immune to
interference.
Jan2002p47-52.pdf (Size: 58.18 KB / Downloads: 75)
Introduction
Man has always been fascinated by the ‘heavenly voices’ from
the skies. This fascination has manifested itself in many mythologies
where he has received divine messages, warnings, and
forecasts from the heavens. It was this undiminished fascination
that kept him working towards the radio system. It was one
hundred years ago that Marconi first transmitted the letter ‘S’
across the Atlantic Ocean. At that time, conveying information
across such large distances was not as much a novelty as the new
concept of broadcasting. While telegraphy was constrained by
physical network of lines, radio reached a widespread, unidentified
audience.
Satellite Orbits
A satellite’s orbit is decided depending on the application. The
geo-stationary orbit (GSO) is considered ideal for broadcast
purposes. It is advantageous because of the ease of tracking – or
rather the lack of tracking. In GSO, even though a satellite
moves at a speed of over 10,000 km per hour, it appears to hang
perfectly motionless in the sky.
Modulation
Modulation is the way information is imparted to the electromagnetic
signal that is referred to as the carrier wave. In
amplitude modulation (AM), the amplitude of the radio frequency
(RF) carrier is made to vary in accordance with the audio
waveform. It is obvious that in this mode, it would be quite
sensitive to additive electrical noise. Frequency modulation
FM has a much better noise immunity, as it is the frequency of
the carrier wave that is varied in a small range according to the
audio waveform. However, noise free reception does not necessarily
mean high fidelity (HiFi).
Digital Radio
Because of the tremendous advancement in digital technology
in the recent years satellite radio is fully digital. In a digital
radio, the transmitter processes sounds into patterns of binary
digits and at the listening end, the digital radio reproduces the
sound from the digits. By using techniques of forward error
control, it is possible to make the reception virtually immune to
interference.