All RF Cafe quizzes make great fodder
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.
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RF Cafe Quizzes.
Note: Some material based on books have quoted passages.
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?
3. 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 pattern
6. What is
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 Keying
8. 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
9. 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 above
10. What is the Z-transform
of the Dirac delta function, δ[n] ?
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answers and explanations.