All RF Cafe quizzes would make perfect fodder for employment interviews for technicians or engineers
- particularly those who are fresh out of school or are relatively new to the work world. Come to
think of it, they would make equally excellent study material for the same persons who are going to
be interviewed for a job.
Some of these books used in quizzes are available as prizes
in the monthly RF Cafe Giveaway.
Note: Many answers contain passages quoted from the text.
quiz challenges your knowledge of digital communications basics.1.
What is meant
by binary frequency shift keying
a) Shifting two frequencies to key a microphone
Using two distinctly different frequencies to represent digital 0s and 1s
c) Shifting digital information at
a binary frequency
d) Half of quadrature shift keying
The constellation to the right indicates what type of modulation?
What is the primary benefit of offset
QPSK (O-QPSK) over QPSK?
a) Greater efficiency
b) Easier to code
c) Constant envelope power
d) No benefit
What is the phase shift for the QPSK modulator block diagram to the right?
What is the image to the right an example of?
a) Tropospheric waveguiding
b) A VCO output
c) A Spirograph drawing
d) An eye pattern6.
the purpose of the lowpass filter (LPF) in the QPSK modulator shown in Question 4?
a) Prevents DC from
entering the mixers
b) Limits the bandwidth of the transmitted signal
c) Adds a DC component to the signal
d) Serves no purpose
What is the spectrum to the right an example of?
a) Frequency Hopping Spread Spectrum
b) Octary Shift
d) Bi-Quadrature Shift Keying8.
Which of the
following items affects the bit error rate (BER) of a received signal?
a) Oscillator phase noise
c) Carrier suppression
d) All the above
Which of these issues presents a problem for zero-IF (direct conversion) receivers?
a) LO leakage creating a DC offset voltage
b) Mixer flicker noise is included in the baseband signal
c) 2nd-order intercept products
d) All the above10.
What is the Z-transform
of the Dirac delta function, δ[n] ?
Need some help? Click here for the
answers and explanations.