Electronics and Telecommunications: Frequency modulation

1. U N I T V
FREQUENCY
MODULATION

2. DEFINATION OF FREQUENCY
MLODULATION (FM)
• Frequency modulation (FM) is a
method of impressing data onto
an alternating-current (AC) wave
by varying the instantaneous
frequency of the wave.
• Frequency modulation is similar in
practice to phase modulation
(PM). When the instantaneous
frequency of a carrier is varied,
the instantaneous phase changes
as well.

3. FREQUENCY MODULATON

4. DIFFERENCE OF AM AND FM
(a) Carrier wave.
(b) Sinusoidal
modulating
signal.
(c) Amplitude-
modulated signal.
(d) Frequency-
modulated signal.

5. CONCEPT OF BANDWIDTH
• In electronic communication, bandwidth is
the range of frequencies that an
electronic signal uses on a given
transmission medium.
• This range is also referred to as the band
and bandwidth literally describes the
difference between the highest-frequency
signal component and the lowest-
frequency signal component.
• Since the frequency of a signal is
measured in hertz (the number of cycles
of change per second), a given bandwidth
is the difference in hertz between the
highest frequency the signal uses and the
lowest frequency it uses.

6. FREQUENCY MODULATION
BANDWIDTH
• In the case of an amplitude modulated signal the bandwidth required is
twice the maximum frequency of the modulation.
• As a frequency modulated signal has sidebands that extend out to infinity, it
is normal accepted practice to determine the bandwidth as that which
contains approximately 98% of the signal power.
• A rule of thumb, often termed Carson's Rule states that 98% of the signal
power is contained within a bandwidth equal to the deviation frequency,
plus the modulation frequency doubled, i.e.:

7. NOISE TRINGLE
• Noise triangle is a triangular noise distribution
for FM.
• Noise triangle is the study of effect of noise on
the carrier signal of the FM wave.

8. PHASE MODULATION

9. PHASE MODULATION
phase modulation, PM, is
used in many applications to
carry both analogue and
digital signals. Keeping the
amplitude of the signal
constant, the phase is varied
to carry the required
information or signal.

10. PULSE CODE MODULATION (PCM)
• Pulse code modulation (PCM) is a digital scheme for
transmitting analog data.
• The signals in PCM are binary; that is, there are only two
possible states, represented by logic 1 (high) and logic 0
(low).
• Using PCM, it is possible to digitize all forms of analog
data, including full-motion video, voices, music.
• To obtain PCM from an analog waveform at the source
(transmitter end) of a communications circuit, the analog
signal amplitude is sampled (measured) at regular time
intervals.

11. PULSE CODE MODULATION (PCM)

12. SAMPLING METHOD
• In signal processing, sampling is the reduction of a continuous
signal to a discrete signal. A common example is the conversion of a
sound wave (a continuous signal) to a sequence of samples (a
discrete-time signal).
• A sample refers to a value or set of values at a point in time and/or
space.
• A sampler is a subsystem or operation that extracts samples from a
continuous signal.
• A theoretical ideal sampler produces samples equivalent to the
instantaneous value of the continuous signal at the desired points.

13. SAMPLING THEOREM

14. PULSE AMPLITUDE MODULATION
• Pulse amplitude modulation (PAM) is the transmission of data by
varying the amplitude s ( voltage or power levels) of the individual
pulses in a regularly timed sequence of electrical or electromagnetic
pulses.
• PAM is only one of several forms of pulse modulation. Other methods
include varying the durations (or widths), the frequencies, the
positions, or the intervals of the individual pulses in a sequence.

15. PULSE TIME MODULATION
• Time characteristics of pulses may also be modulated with intelligence
information.
• Two time characteristics may be affected:
• (1) the time duration of the pulses, referred to as PULSE-DURATION MODULATION
(PDM) or PULSE-WIDTH MODULATION (PWM)

16. PULSE POSITION MODULATION
• The amplitude and width
of the pulse is kept
constant in the system.
The position of each
pulse, in relation to the
position of a recurrent
reference pulse, is varied
by each instantaneous
sampled value of the
modulating wave.

17. MULTIPLEXING
• Multiplexing is sending multiple signals or streams of
information on a carrier at the same time in the form of a
single, complex signal and then recovering the separate
signals at the receiving end.
• In analog transmission, signals are commonly multiplexed
using frequency-division multiplexing (FDM), in which the
carrier bandwidth is divided into sub-channels of different
frequency widths, each carrying a signal at the same time in
parallel.
• In digital transmission, signals are commonly multiplexed
using time-division multiplexing (TDM), in which the multiple
signals are carried over the same channel in alternating time
slots.

18. MULTIPLEXING

19. MULTIPLEXING