ECGR4124 Project 8, Modulated Signal Spectra
Form the same groups of 3 as before. Members of any group must
be
all graduate or all undergrad.
Do NOT use "zoom" feature on
any
plots unless specifically requested.
Preliminary tasks
- Run NetBeans
5.5, or a later version
(Start>AllPrograms>MosaicXp>Programming>Netbeans>NetBeans55)
- Make a copy of your previous project from within NetBeans, and
rename
the new project.
- Make
sure
that your 20log10|FFT| is working correctly, with dc
(zero-frequency) in the center of the plot.
- Plot the spectrum of
iqmod.au (use your centered FFT spectrum plotting function
from the earlier project, 20log10|FFT| ) . (
P1 )
This is a QPSK (Quadrature Phase Shifk Keying) modem at 1 KHz
carrier
frequency. Note that the majority
of the signal energy is concentrated near this frequency.
Ignore the
harmonics and noise in the spectrum at higher frequencies.
Note: make sure that your
FFT
from the earlier project had no errors!
- Plot the spectrum of mod.au. ( P2 )
This is a DSB-SC signal at 2 KHz carrier frequency. Note that
the
majority of the signal energy is concentrated in the two
sidebands near
this frequency. Ignore the harmonics and noise in the spectrum
at
higher frequencies.
- Plot the spectrum of iqmodint.au. (
P3 )
This is a QPSK modem at 1 KHz carrier frequency plus
interference from
a DSB-SC signal and noise. Note that the majority of the
signal energy
is concentrated near the 1KHz modem frequency.
- Add a function (F4 button) to display the first 512 points
of
the above 3 files (iqmod.au, iqmodint.au, mod.au). Plot and
display the
first 512 time-domain points for all three files. ( iqmod.au P4,
iqmodint.au P5, mod.au P6 )
Hint:
- Design and implement a lowpass filter (as the "F1" key) to
reduce the noise and
interference in iqmodint.au. Use a moving average filter as in
Eq.
2.91. Design the filter so that the first null is at 2 KHz.
(See Fig.
2.19 on p. 45).
It would be best to implement this as a class-member function
(it will
be needed later) that accepts the signal and the filter length
M as
inputs, and
that gives the filtered signal as an output.
Do not implement this filter using the FFT, implement it as a
linear
filter in the time
domain.
Plot the spectrum of the filtered signal (iqmodint.au after
filtering). ( P7 )
- Compare the filtered and unfiltered spectra of the modem
signal from above. What is the reduction in dB of the
DSB-SC
interference?. ( Q1 )
Report
Use the Project
Report Template
(also shown as pdf file)
Include the plot numbers P1, P2, etc
in
captions, along with a short description!
Write a cover sheet + 1 page executive
summary ONLY!!! Describe any unresolved issues.
Place answers to all questions on one or more consequitive sheets
of paper at the front of the report!
Do NOT scatter
the question answer sheets throughout the report, keep them
together
Do NOT use "zoom" feature on
any
plots unless specifically requested.
Make sure that you include question
numbers and plot numbers on all sheets!
I will only look on the question answer-sheets for any discussion.
All extraneous material WILL BE
IGNORED!
Do not write any discussion, except directly on the question
answer-sheets or 1 page summary.
Do not add extraneous pages.
Do not put explanations on plots unless
specifically directed to do so.
Include any problems or unresolved issues in the summary.
Copyright 2009 T.P. Weldon