Digital Signal Processing Reference
In-Depth Information
Exercises on Chapter 8
Exercise 1 Amplitude modulation AM
(a)
Develop the circuit corresponding to Illustration 151 by means of the module “Cut
out”.
(b)
Investigate the frequency spectrum according to Illustration 151 experimentally
using DASY
Lab
. Set the values so that the instantaneous frequency begins at t = 0s
and the other ends at t = 1 s. Therefore, select f = 2,4,8 Hz and all the instantaneous
frequencies as a power of two. The block length and sampling rate should be set as
in the past at the standard setting of 1024.
(c)
Create the circuit corresponding to Illustration 152 and Illustration 153. As the
source signal take lowpass filtered noise.
(d)
Develop an AM generator with which by means of a manual regulator the carrier
frequency f
carrier
, the signal amplitude Û
LF
and the offset can be set.
(e)
Develop an AM generator by means of the module “formula interpreter” which
implements the AM formula given on page 236 and with which the degree of
modulation m, f
LF
and f
carrier
can be set. Select Û
LF
= 1 V .
Exercise 2 Demodulation of an AM signal
(a)
Develop the demodulation circuit corresponding to Illustration 154. Rectification
should be shown by the „absolute value“ process (module “arithmetics”), the RC
circuit by lowpass filtering. See also Illustration 155.
(b)
Vary the offset and examine the spectra of the modulated signals according to
Illustration 155.
(c)
Why is the double sideband with a carrier a disadvantageous process.
Exercise 3 Single sideband modulation EM
(a)
Design the circuit for the EM according to Illustration 160.
(b)
Set the parameters according to Illustration 160. Select as always the sampling rate
and blocklength at 1024. The same carrier is used here for modulation and recon-
version or demodulation.
(c)
Why is the demodulated source signal time staggered?
(d)
Design the circuit for the upper and lower sideband according to Illustration 160 and
Illustration 161.
Exercise 4 Frequency multiplex processes
(a)
Design the circuit for the formation of pre-groups and reconversion according to
Illustration 166 and Illustration 167. The bandwidth of the source signal - filtered
noise - corresponds precisely to the bandwidth of a telephone signal of 300 -3400
Hz.
(b)
Take your final test in the use of DASY
Lab
and design a suitable circuit for the
