Electronics Systems And Technologies
Priority Level: High (ECE) & Low (ECT)
- 1.The reflected wave
- A.
Arrives in phase with the direct wave
- B.
Arrives out of phase with the direct wave
- C.
Arrives in a variable phase compared with the direct wave
- D.
Is always horizontally polarized
- 2.An advantage of FSK over on/off keying is the fact that FSK
- A.
Offers better frequency stability
- B.
Can provide faster data rates
- C.
Reduces the number of receiving errors
- D.
Forget it! On-off keying is just as good as FSK
- 3.The highest layer of the ionosphere is
- A.
The D layer
- B.
The E layer
- C.
The F layer
- D.
None of the above
- 4.An LSB, suppressed-carrier signal can be demodulated by
- A.
An envelope detector
- B.
A diode
- C.
A ratio detector
- D.
A product detector
- 5.Which of the following modes is used to send image data over telephone lines?
- A.
On/off keying
- B.
Fax
- C.
AM
- D.
Product detection
- 6.The S/N ratio is a measure of
- A.
The sensitivity of a receiver
- B.
The selectivity of a receiver
- C.
The dynamic range of a receiver
- D.
The efficiency of a transmitter
- 7.A receiver that responds to a desired signal, but not to another signal very close by in frequency, has good
- A.
Sensitivity
- B.
Noise figure
- C.
Dynamic range
- D.
Selectivity
- 8.An FM detector with built-in limiting is
- A.
A ratio detector
- B.
A discriminator
- C.
An envelope detector
- D.
A product detector
- 9.In which mode of PM does the peak power level of the pulses vary?
- A.
PAM
- B.
PDM
- C.
PIM
- D.
PFM
- 10.Which of the following modes can be demodulated with an envelope detector?
- A.
AM
- B.
CW
- C.
FSK
- D.
USB
- 11.The bandwidth of a fax signal is kept narrow by
- A.
Sending the data at a slow rate of speed
- B.
Maximizing the number of digital states
- C.
Optimizing the range of colors sent
- D.
Using pulse modulation
- 12.The dynamic range in a superhet is largely influenced by the performance of the
- A.
Local oscillator
- B.
Product detector
- C.
Front end
- D.
Selectivity in the IF chain
- 13.Frequency sweeping can be used to get a transmitter to produce
- A.
Spread-spectrum signals
- B.
Time division multiplexed signals
- C.
Narrowband AM signals
- D.
Double sideband, suppressed carrier signals
- 14.A radio wave has a frequency of 1.55 MHz. The highest modulating frequency that can be used effectively is about
- A.
1.55 kHz
- B.
15.5 kHz
- C.
155 kHz
- D.
1.55 MHz
- 15.If an AM signal is modulated with audio having frequencies up to 5 kHz, then what is the complete signal bandwidth?
- A.
10 kHz
- B.
20 kHz
- C.
50 kHz
- D.
500 kHz
- 16.Suppose an SSB suppressed carrier is at 14.335 MHz, and audio data is contained in a band from 14.335 to 14.338 MHz. What is this mode?
- A.
DSB
- B.
LSB
- C.
USB
- D.
AFSK
- 17.The deviation of a narrowband voice FM signal normally extends up to __________ either side of the unmodulated-carrier frequency.
- A.
3 kHz
- B.
5 kHz
- C.
10 kHz
- D.
3 MHz
- 18.A continuously variable signal (such as music audio) can be recovered from a signal having only a few discrete levels or states by means of
- A.
A ratio detector
- B.
A D/A converter
- C.
A product detector
- D.
An envelope detector
- 19.Transmitting and receiving independent signals over a common signal path by means of synchronized switches at each end of the transmission line so that each signal appears on the line only a fraction of time in an alternating pattern.
- A.
FDM
- B.
AFSK
- C.
PCM
- D.
TDM
- 20.It states that a signal can be exactly reconstructed from its samples if the sampling frequency is greater than twice the highest frequency of the signal; but requires an infinite number of samples.
- A.
Nyquist–Shannon sampling theorem
- B.
Maxwell's theorem
- C.
Hartley's sampling theorem
- D.
Pascal-Blaise theorem
- 21.Imagine a center-fed, straight wire antenna in free space, whose length can be varied at will. At which of the following lengths is the radiation resistance at the feed point the highest?
- A.
λ/4
- B.
λ
- C.
λ/3
- D.
λ/2
- 22.What is the approximate length, in meters (m), of a center-fed, λ/2 wire antenna at a frequency of 18.1 MHz? Assume the velocity factor is typical for wire.
- A.
7.90 m
- B.
8.29 m
- C.
13.6 m
- D.
25.9 m
- 23.What is the approximate height, in feet (ft), of a ground-mounted, λ/4 vertical antenna, made of aluminum tubing, at a frequency of 7.025 MHz? Assume the velocity factor is 92 percent.
- A.
64.43 ft
- B.
32.22 ft
- C.
19.64 ft
- D.
9.822 ft
- 24.In order to obtain reasonable efficiency with a λ/4 vertical antenna mounted over poorly conducting soil at a frequency of 10 MHz, it is necessary to
- A.
Minimize the loss resistance by installing numerous ground radials
- B.
Make the antenna out of large-diameter aluminum or copper tubing
- C.
Suspend the antenna from a kite or balloon
- D.
Feed the antenna with a waveguide
- 25.A driven element in a parasitic array is
- A.
Grounded for dc
- B.
A loop with a circumference of λ/2
- C.
Connected to the feed line
- D.
A straight length of wire
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