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1594 practice sets · Page 56 of 80
The error probability of a PCM is
Calculated using power spectral density
Calculated using noise and inter symbol interference
All of the above
Gaussian noise + error component due to inter symbol interference
In PCM, the parameter varied in accordance with the amplitude of the modulating signal is
Phase
Amplitude
None of the above
Frequency
The modulation techniques used to convert analog signal into digital signal are
Adaptive delta modulation
Pulse code modulation
All of the above
Delta modulation
One factor in the accuracy of a reconstructed PCM signal is the
Number of bits used for quantization
Signal bandwidth
Baud rate
Carrier frequency
Modulation is used to
Ensure that information may be transmitted over long distances
Reduce the bandwidth
Allow the use of practicable antennas
Separate differing transmission
In modems
Digital signal is amplified
Several digital signal are multiplexed
None of these above
A digital signal changes some characteristics of a carrier wave
In PCM
Non-linear coding scheme is undertaken
Digital signal is converted into analog signal
None of these
Pulse Amplitude modulation samples are quantized
The qualifier differential to PSK means that
phase shift is with reference to the previous bit transmitted
it uses phase shifts of multiple of 90 degree
none of these above
it uses phase shifts of 180 degree
ASK is rarely used in modems because
it takes care of amplitude only
it shifts only between ON and OFF states
none of the above
it is highly susceptible to noise
ASK is a result of combination of Shift keying and
Amplitude modulation
Digital modulation
None of these above
Analog modulation
Codec uses
PCM and Delta modulation
Pulse code modulation technique only
None of these
Delta modulation only
Two binary values are represented by two different frequencies in :
phase-shift-keying
amplitude-shift-keying
none of these above
frequency-shift-keying
The condition for maximum efficiency for a D.C. generator is
eddy current losses = stray losses
hysteresis losses = eddy current losses
copper losses = 0
variable losses = constant losses
The armature voltage control of D.C. motor provides
constant torque drive
constant voltage drive
constant current drive
none of the above
The armature torque of the D.C. shunt motor is proportional to
field flux only
armature current only
both a and b
none of the above
Starters are used with D.C. motors because
these motors have high starting torque
these motors are not self-starting
back e.m.f. of these motors is zero initially
to restrict armature current as there is no back e.m.f. while starting
Speed control by Ward Leonard method gives uniform speed variation
in one direction
in both directions
below normal speed only
above normal speed only.
Sparking, is discouraged in a D.C. motor because
it increases the input power con-sumption
commutator gets damaged
both a and b
none of the above
Sparking at the commutator of a D.C. motor may result in
damage to commutator segments
damage to commutator insulation
increased power consumption
all of the above
Regenerative method of braking is based on that
back e.m.f. is less than the applied voltage
back e.m.f. is equal to the applied voltage
back e.m.f. of rotor is more than the applied voltage
none of the above
