Amplitude Shift Keying and Frequncy Shift Keying

[dona1590]

I am doing this project and i am finding it difficult with the section that has to do with the explanation of how digital information is modulated, transmitted and received in ASK and FSK modulating schemes

 

[mbarazeen]

if you can post the explanation where you have dificulty to understand some body can help you, if you ask in general there will be a lot to explain.

 

[georgetwo]

Amplitude-shift keying (ASK) is a
form of modulation that represents
digital data as variations in the
amplitude of a carrier wave.
The amplitude of an analog carrier
signal varies in accordance with the
bit stream (modulating signal),
keeping frequency and phase
constant. The level of amplitude can
be used to represent binary logic 0s
and 1s. We can think of a carrier
signal as an ON or OFF switch. In
the modulated signal, logic 0 is
represented by the absence of a
carrier, thus giving OFF/ON keying
operation and hence the name
given.
Like AM, ASK is also linear and
sensitive to atmospheric noise,
distortions, propagation conditions
on different routes in PSTN, etc.
Both ASK modulation and
demodulation processes are
relatively inexpensive. The ASK
technique is also commonly used to
transmit digital data over optical
fiber. For LED transmitters, binary 1
is represented by a short pulse of
light and binary 0 by the absence of
light. Laser transmitters normally
have a fixed "bias" current that
causes the device to emit a low light
level. This low level represents
binary 0, while a higher-amplitude
lightwave represents binary

 

[georgetwo]

Frequency-shift keying (FSK) is
a frequency modulation scheme in
which digital information is
transmitted through discrete
frequency changes of a carrier
wave. The simplest FSK is binary
FSK (BFSK). BFSK literally implies
using a pair of discrete frequencies
to transmit binary (0s and 1s)
information. With this scheme, the
"1" is called the mark frequency and
the "0" is called the space frequency.
The time domain of an FSK
modulated carrier is illustrated in the
figures to the right.