TRUE or FALSE: A small, fixed
phase offset in the receiver demodulatingAM with suppressed carrier produces an undesirable low frequency
modulated version of the analog message.
Try different frequency offsets
gam
,
,
,
.
How well does the recovered message
match the actual message
?
For each case, what is the spectrum of
? Hint: look over
more than just the first
second to see the effect.
Consider the system shown in
[link] .
Show that the output of the system is
, as indicated.
Create a M
atlab routine to implement the square-law mixing
modulator of
[link] .
Create a signal
that has bandwidth 100 Hz
Modulate the signal to 1000 Hz.
Demodulate using the AM demodulator from
AM.m (to recover the original
).
Exercise
[link] essentially creates a
transmitter and receiver based on the square-law modulator(rather than the more standard mixing modulator).
Using this system:
Show how the received signal degrades if the
phase of the cosine wave is not known exactly.
Show how the received signal degrades if the
frequency of the cosine wave is not exact.
Show how the received signal degrades if the
bandpass filter is not centered at the specified frequency.
Consider the transmission system of
[link] .
The message signal
has magnitude spectrum
shown in part (a).The transmitter in part (b) produces the
transmitted signal
which passes through the
channel in part (c). The channel scales thesignal and adds narrowband interferers to create
the received signal
.
The transmitter and channel parameters are
radians,
kHz,
kHz,
kHz,
kHz, and
kHz.
Thereceiver processing
is shown in
[link] (d).
All bandpass and lowpass filters are considered ideal with a gainof unity in the passband and zero in the stopband.
Sketch
for
kHz
30kHz.
Clearly indicate the amplitudes and frequencies of key points in the sketch.
Assume that
is chosen to maximize the magnitude of
and reflects the value of
and the delays
imposed by the two ideal bandpass filters that form thereceived signal
.
Select the receiver parameters
,
,
, and
,
so the receiver output
is a scaled version of
.
An analog baseband message signal
has all energy between
and
Hz.
It is upconverted to the transmitted passband signal
via AM with suppressed carrier
where a carrier frequency
.
The channel is a pure delay and the received signal
is
where the delay
is an integer multiple
of the carrier period
(
) plus a fraction of
given by
.
The mixer at the receiver is perfectly synchronizedto the transmitter so that the mixer output
is
The receiver mixer phase may not match the transmitter
mixer phase
.
The receiver lowpass filters
to produce
where the lowpass filter is ideal with unity passband gain, linear
passband phase with zero phase at zero frequency, and cutoff frequency
.
Write a formula for the receiver mixer output
as a function of
,
,
,
,
, and
(without use of
,
,
, or
).
Determine the amplitude of the minimum and maximum values of
for
.
For
,
,
radians, and
sec,
determine
that maximizes the magnitude of the maximum and minimum
values of
.
Questions & Answers
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a fixed gas of a mass is held at standard pressure temperature of 15 degrees Celsius .Calculate the temperature of the gas in Celsius if the pressure is changed to 2×10 to the power 4