RC Exam - EST 01 to EST 10

Answers to RC Exams from EST 01 to EST 10

In what portion of the atmosphere does the majority of weather phenomena take place?

Troposphere

Which of the following is NOT a factor for radio wave refraction?

Transmitter power

A certain tropospheric system has scatter angle components of 0.2 and 0.3 radians respectively. Determine the scatter angle oftentimes called the angular distance between antennas.
0.06 rad
0.25 rad
0.50 rad
0.24 rad

0.50 rad

At what approximate time of day is the density of the ionospheric layers at its lowest level?
Afternoon
Just before sunrise
Sunset
Mid-morning

Just before sunrise

Radio waves above the MUF will experience what effect when refracted from the ionosphere?
They will overshoot the desired location
They will be absorbed by lower layers
They will fall short of the desired location
They will experience multipath fading

Just before sunrise

In signal processing, what is the simplest form of smoothing which simply replaces each data value with the average of neighboring values?
Direct average
Replacing average
Moving average
Substitution average

Moving average

During the 27-day sunspot cycle, which ionospheric layer experiences the greatest fluctuations in density?
F₁
D
E
F₂

F2

Determine the noise current for a diode with a forward bias of 1 mA over a 100-kHz bandwidth.
0.566 µA
0.000566 µA
0.00566 µA
0.0566 µA

0.00566 µA

i\=sqrt(B2iq)

q\= 1.6x10^-19

When sudden ionospheric disturbances (SID) occurs, which ionospheric layer is affected the most?
D
E
F₂
F₁

D

Which of the following factors will affect the outer limits of the skip zone?
Angle of transmission
Frequency
Sunspot activity
All of the choices

All of the choices

What converts a finite list of equally-spaced samples of a function into the list of coefficients of a finite combination of complex sinusoids, ordered by their frequencies, that has those same sample values?
Discrete Wavelet Transform (DWT)
Continuous Wavelet Transform (CWT)
Wigner Transform
Discrete Fourier transform (DFT)

Discrete Fourier transform (DFT)

The critical angle for radio wave propagation depends on what two factors?
Angle of incidence and layer density only
Wavelength and antenna height only
Angle of incidence and wavelength only
Layer density and wavelength only

Layer density and wavelength only

The total distance between two points on earth is 20 miles. What is earth's curvature when surface refractivity is 250?
52.4 mi
54.2 mi
30.1 mi
10.8 mi

54.2 mi

or 54.4 if using exact numbers

What is the art and science of modifying acquired time-series data for the purposes of analysis or enhancement?
Signal Processing
Signal Gathering
Signal Sampling
Signal Acquisition

Signal Processing

Fading on the majority of the ionospheric circuits is a result of what particular type of fading?
Absorption
Selective
Weather
Multipath

Multipath

The regular variations in the ionosphere can be separated into how many classes?
Four
Two
Three
Five

four

Variations in the ionosphere resulting from changes in the sun's activity are known as
Both regular and irregular variations
irregular variations
regular variations
seasons

Both regular and irregular variations

The frequency of ultraviolet light passing through the atmosphere has what relationship to the ionospheric layer it ionizes?
It is inversely proportional during the day and directly proportional at night
It is inversely proportional
It is directly proportional
It is directly proportional during the day and inversely proportional at night

It is inversely proportional

What is used in digital signal processing and discrete-time control theory to transform continuous-time system representations to discrete-time and vice versa?
Continuous Wavelet Transform (CWT)
Wigner Transform
Bilinear transform
Discrete Wavelet Transform (DWT)

Bilinear transform

In relation to troposcatter system parameter, what is the typical transmitter power for path distance of 150-250 km at 1 GHz frequency?
5 KW
7 kW
1 kW
3 kW

1 kW

For a signal measurement of -42 dBm, a noise measurement of 16 dBrnC, and a -40 dBm TLP, determine the signal level in dBrnC.
32 dBrnC
40 dBrnC
74 dBrnC
48 dBrnC

48 dBrnC

What transform is similar to the Fourier transform in that it is a decomposition of a signal in terms of a basis set of functions?
Discrete Fourier transform (DFT)
Discrete Wavelet Transform (DWT)
Continuous Wavelet Transform (CWT)
Bilinear Transform

Discrete Wavelet Transform (DWT)

A 1004-Hz test tone is transmitted over a telephone circuit at 0 dBm and received at -16 dBm. Determine the 1004-Hz circuit gain.
+16 dB
32 dB
0 dB
-16 dB

-16 dB

Gain \= 0dBm - 16 dBm
\= -16 or 16 loss

In signal processing, what removes short-term variations, or "noise" to reveal the important underlying form of the data?
Filtering
Chopping
Smoothing
Leveling

Smoothing

What transform maps a 1D time signal U(t) into a 2D time-frequency representation?
Hilbert Transform
Wigner Transform
Continuous Wavelet Transform (CWT)
Fourier Transform

Wigner Transform

The only roadblock to having a complete receiver manufactured on an integrated circuit is \______.
phase-locked loops
cost
tuned circuits and volume controls
ceramic filters

tuned circuits and volume controls

Which one of the following types of noise becomes of great importance at high frequencies?
Impulse noise
Transit-time noise
Shot noise
Random noise

Transit-time noise

In amplitude modulation, bandwidth is \_____ the audio signal frequency.
twice
thrice
four times
none of the choices

twice

If the 3-dB bandwidth of a tuned circuit is 10 MHz then what is its actual noise bandwidth?
3.18 MHz
15.7 MHz
31.4 MHz
20 MHz

15.7 MHz

In SSB generation, filter method is the simplest method to eliminate one of the two sidebands. Find the Q required of the filter to have an effective 80 dB sideband suppression. Assume a carrier of 15 MHz and 200 Hz separation between two sidebands.
1875 x 10⁶
187.5 x 10⁶
18.75 x 10⁶
1.875 x 10⁶

1.875 x 10⁶

Q \= (f_c*sqrt(antilog (dB/20))/4deltaF)

An AM signal is being measured by an oscilloscope. The following are the readings:V_max(p-p) \= 6.9 divisions from the graticule on the scopeV_min(p-p) \= 2.2 divisions from the graticule on the scopeIf the vertical scale is 1.5 V per division, what is the carrier voltage?
7.05 V
6.825 V
13.65 V
3.525 V

6.825 V

V_c\= (Vmax+Vmin)/2 * division

What is another name for signals in the HF range?
RF waves
Microwaves
Shortwaves
Millimeter waves

Shortwaves

Indicate the noise whose source is in a category different from that of the other three.
Atmospheric noise
Solar noise
Cosmic noise
Galactic noise

Atmospheric noise

An FM receiver rarely works satisfactorily without an RF amplifier because \______.
FM receivers do not have very much gain in their IF amplifier stages
FM receivers typically work with smaller input signal levels due to their noise characteristics
FM receivers need RF amplifier stages to be able to decode stereo signals
FM receivers have a narrower bandwidth

FM receivers typically work with smaller input signal levels due to their noise characteristics

A high-level modulation AM transmitter has a DC supply to the final RF power amplifier of 50 V. If the total current is 5 A and the efficiency is 85%, how much AF power is required for 100% modulation?
62.5 W
250 W
500 W
125 W

P \= IV
P_m \= Ptotal/2

Amplitude modulation is used for broadcasting because \______.
compared with other system it requires less transmitting power
no other modulation system can provide the necessary bandwidth for high fidelity
it is more noise immune than other modulation system
it use avoids receiver complexity

it use avoids receiver complexity

A tuned circuit has a capacitance of 25 pF and a dynamic resistance of 1.6 kΩ. Determine the noise bandwidth.
0.625 MHz
625 MHz
62.5 MHz
6.25 MHz

6.25 MHz

BW_N\= 1 /(4RC)

In amplitude modulation, suppose the unmodulated antenna current is 2.5 A and the modulated antenna current is 2.8 A, what is the modulation index?
0.65
0.71
0.90
0.35

0.71

m \= sqrt(2(I_t/I_c)^2 -1 )

AM BC signals are normally having \________ polarization.
horizontal
vertical
random
circular

vertical

If a receiver has poor capacity of blocking adjacent channel interference then the receiver has \______.
poor sensitivity
poor signal to noise ratio
poor selectivity
poor front end

poor selectivity

An SSB transmitter produces a peak-to-peak voltage of 200 V across a 100-Ω antenna load. What is the peak envelope power?
200 W
100 W
50 W
400 W

50 W

In high level amplitude modulation,
collector modulation method is high level amplitude modulation
power amplifiers are used to boost the carrier and modulating signals before modulation
modulation is done at high power of carrier and modulating signal
All of the choices

All of the choices

What is the typical power of educational FM stations?
10 W
15 W
20 W
5 W

10 W

In frequency modulation, determine the possible frequency deviation produced by noise. Assume a maximum modulating frequency and a desirable S/N for voice transmission.
859 Hz
28.65 Hz
85.9 Hz
859 kHz

859 Hz

The AM spectrum consists of \________.
All of the choices
upper side band frequency
carrier frequency
lower side band frequency

All of the choices

A double-tuned IF amplifier with optimum coupling has a critical coupling of 0.02 and a resonant frequency of 5 MHz. Find the overall bandwidth.
150 kHz
50 kHz
200 kHz
100 kHz

150 kHz

Optimum Coupling \= 1.5 Critical Coupling

Overall BW\= Optimum Coupling* Resonant Freq

In an SSB transmitter, if the peak envelope power (PEP) is 500 W then what is typical range of the average power?
167 W to 250 W
100 W to 200 W
125 W to 250 W
125 W to 167 W

125 W to 167 W

What is the purpose of a buffer amplifier stage in a transmitter?
It prevents transmitters from producing spurious frequencies in the output signals.
It provides power amplification with high efficiency.
It amplifies audio frequencies before modulation occurs.
Its high input impedance prevents oscillators from drifting of frequency.

Its high input impedance prevents oscillators from drifting of frequency.

When radiowave signals follow the curvature of the earth, this is known as \______.
troposheric scatter
ducting
ionospheric reflections
the faraday effect

ducting

The value of the resistor creating thermal noise is doubled. The noise power generated is therefore \_____.
quadrupled
unchanged
double
halved

unchanged

In the stabilized reactance modulator AFC system, \_____.

the discriminator must have a fast time constant to prevent demodulation

the higher the discriminator frequency, the better the oscillator frequency stability

phase modulation is converted into FM by the equalizer circuit

the discriminator frequency must not be too low, or the system will fail

the discriminator frequency must not be too low, or the system will fail

In an SSB transmitter, one is most likely to find a \______.
tuned modulator
class B RF amplifier
class A RF output amplifier
class C audio amplifier

class B RF amplifier

What are some reasons not to use parallel-conductor transmission line?

It is difficult to make at home, and it does not work very well with a high SWR

You must use an impedance-matching device with your transceiver, and it does not work very well with a high SWR

It does not work well when tied down to metal objects, and you should use a balun and may have to use an impedance-matching device with your transceiver

It does not work well when tied down to metal objects, and it cannot operate under high power

It does not work well when tied down to metal objects, and you should use a balun and may have to use an impedance-matching device with your transceiver

What usually happens to radio waves with frequencies below the maximum usable frequency (MUF) when they are sent into the ionosphere?
They are bent back to the Earth
They are changed to a frequency above the MUF
They pass through the ionosphere
They are completely absorbed by the ionosphere

They are bent back to the Earth

A microstrip transmission line is to be used as a capacitor of 4 pF at 800 MHz. The PCB dielectric is 3.6. The microstrip dimensions are h \= 0.0625 in., w \= 0.13 in., and t \= 0.002 in. What is the characteristic impedance of the line?
276 Ω
49 Ω
50 Ω
75 Ω

49 Ω

A basic parallel-wire line has a diameter of 0.023 in. with a spacing of 0.5 in. apart. The dielectric is a continuous polyvinyl chloride (PVC). What is its characteristic impedance?
286 Ω
301 Ω
249 Ω
452 Ω

249 Ω

The characteristic impedance of a parallel wire transmission line does not depend on the:
velocity of energy on the line
center to center distance between conductors
dielectric
radius of the conductors

velocity of energy on the line

In tropospheric scatter propagation, if the surface refractivity at the transmitting section is 205 and at the receiving section is 201 then what is the actual surface refractivity?
403
203
406
205

203

Average

An SWR meter measures the degree of match between transmission line and antenna by:
comparing forward and reflected voltage
measuring radiated RF energy
measuring the conductor temperature
inserting a diode in the transmission line

comparing forward and reflected voltage

In transmission engineering, longitudinal balance is an important parameter when dealing with transmission lines carrying baseband signals such as subscriber loops. When the open circuit longitudinal voltage is 12 V and the metallic voltage is 5 V, determine the longitudinal balance of the line.
-7.6 dB
7.6 dB
3.8 dB
-3.8 dB

7.6 dB

Why does coaxial cable make a good antenna transmission line?
It can be used near metal objects, and its impedance is higher than that of most amateur antennas

You can make it at home, and its impedance matches most amateur antennas

It is weatherproof, and its impedance matches most amateur antennas

It is weatherproof, and its impedance is higher than that of most amateur antennas

It is weatherproof, and its impedance matches most amateur antennas

A 75 ohm transmission line could be matched to the 300 ohm feed point of an antenna:
by inserting a diode in one leg of the antenna
by using a 4 to 1 impedance transformer
by using a 4 to 1 trigatron
with an extra 250 ohm resistor

by using a 4 to 1 impedance transformer

What does the term y(-1) indicate especially in an equation that represents the behavior of the causal system?
Response of the system to its initial input
Negative initial condition of the system
Negative feedback condition of the system
Initial condition of the system

Initial condition of the system

Modulation produced in the plate circuit of the last radio stage of a system is known by what term?
Radio frequency modulation
High-level modulation
Final-amplifier modulation
Low-level modulation

High-level modulation

An equalizer used to compensate the distortion in the communication system by faithful recovery of an original signal is nothing but an illustration of \_________.
dynamic system
static system
None of the choicesContinuous-wave
invertible system

invertible system

Which of the following types of modulation is a form of amplitude modulation?
Continuous-wave
Frequency
Angle
Phase

Continuous-wave

What is the maximum distance along the Earth's surface that is normally covered in one hop using the F2 region?
2000 km
None

the F2 region does not support radio-wave propagation
300 km
4000 km;4000 km

The primary advantage of phase modulation over frequency modulation is that phase modulation has better carrier \_______.
frequency stability
amplitude stability
directional stability
power stability

frequency stability

Which among the following belongs to the category of non-recursive systems?
Non-causal IIR Systems
Non-causal FIR Systems
Causal IIR Systems
Causal FIR Systems

Causal FIR Systems

A stripline is a flat conductor sandwiched between two ground planes. Find its characteristic impedance with the following information given: PCB dielectric is 2.2.

d \= 0.5 in; w \= 0.3 in; t \= 0.2 in and h \= 0.4 in.
56 Ω
75 Ω
112 Ω
36 Ω;36 Ω

Indicate the false statement regarding the Armstrong modulation system,
Equalization is unnecessary.
the system is basically phase and not frequency, modulation.
Frequency multiplications must be used
AFC is not needed, as the crystal oscillator is used.

Equalization is unnecessary.

Which kind of frequency spectrum/spectra is/are obtained from the line spectrum of a continuous signal on the basis of Polar Fourier Series Method?
Continuous in nature
Sampled in nature
All of the choices
Discrete in nature

Discrete in nature

A coaxial line has an inner diameter of 0.2 in. and a center conductor of 0.06 in. diameter. If the insulation is polyethylene then what is its characteristic impedance?
48 Ω
144 Ω
40 Ω
50 Ω

48 Ω

In the spectrum of a frequency modulated wave:
the carrier frequency cannot disappear
the carrier frequency disappears when the modulation index is large
the amplitude of any sideband depends on the modulation index
the total number of sidebands depend on the modulation index

the amplitude of any sideband depends on the modulation index

What causes the ionosphere to form?
Lightning ionizing the outer atmosphere
Release of fluorocarbons into the atmosphere
Temperature changes ionizing the outer atmosphere
Solar radiation ionizing the outer atmosphere

Solar radiation ionizing the outer atmosphere

When a dc voltage is applied to a transmission line and the load absorbs all the energy, what is the resulting relationship between current and voltage?
They are in phase with each other
They are evenly distributed along the line
They are equal to Z₀ of the line
They are out of phase with each other

They are evenly distributed along the line

Calculate the length of a practical half-wave dipole for a frequency of 15 MHz.
7.5 m
10.5 m
9.5 m
8.5 m

9.5 m

When a person is standing in an rf field, power in excess of what level will cause a noticeable rise in body temperature?
10 mW
5 mW
15 mW
20 mW

10 mW

Hertz antennas are designed to operate at what wavelength in relationship to their operating frequency?
Full-wave
Quarter-wave
Three quarter-wave
Half-wave

Half-wave

Marconi antennas are used for operating frequencies below what level?
4 MHz
10 MHz
2 MHz
6 MHz

2 MHz

What is the typical channel capacity of a troposcatter system for 1 GHz frequency and path distance of 250-320 km?
240 channels
36 channels
84 channels
72 channels

36 channels

For an AM receiver, if the capacitance tuning range is 10, what is the frequency tuning range?
5
100
3.16
20

3.16

What effect do ionospheric storms have on the range of frequencies and the working frequency used for communications?
Decrease

increase
Increase; increase
Increase; decrease
Decrease; decrease ;Decrease; decrease

A standard AM receiver tunes from 535 to 1605 kHz. Determine its frequency tuning range.
2.04
2.08
2.03
2.05

A standard AM receiver tunes from 535 to 1605 kHz. Determine its frequency tuning range.

If an antenna is too short for the wavelength being used, what electrical compensation must be introduced for the antenna to achieve resonance?
Lumped resistance
More power
Lumped inductive reactance
Lumped capacitive reactance

Lumped inductive reactance

Capacitive top-loading helps to increase which of the following antenna characteristics?
Radiation efficiency
Bandwidth
Power-handling
Directivity

Bandwidth

Calculate the gain, with respect to an isotropic antenna, of a half-wave dipole with an efficiency of 90% that is placed one-quarter-wavelength from a plane reflector that reflects 100% of the signal striking it.
8.76 dBi
8.67 dBi
7.86 dBi
7.68 dBi

7.68 dBi

What determines the gain and directivity of a rhombic antenna?
Transmitter power
Transmitted frequency
Radiated wave interaction
Antenna height

Radiated wave interaction

Of the following methods, which is NOT used to feed a cylindrical paraboloid reflector?
A quarter-wave stub
A thin waveguide radiator
A slit in the side of a waveguide
A linear array of dipoles

A quarter-wave stub

Frequencies above what level pass through the E layer unaffected?
150 MHz
200 MHz
50 MHz
100 MHz

150 MHz

A sector log-periodic array can act as an antenna for a minimum of what number of transmit or receive systems?
3
2
4
5

4

For a total rain attenuation of 11 dB, what is the sky noise at 20 GHz? Assume that the mean absorption temperature of the attenuating medium is 275 K.
253.16 K
255.19 K
221.18 K
273.18 K

253.16 K

What is the antenna beamwidth in degrees if the power gain is 30 dB?
8.4ᵒ
5.4ᵒ
6.4ᵒ
7.4ᵒ

6.4ᵒ

All antennas regardless of their shape or size have how many basic characteristics?
5
2
4
3

4

A 10 MHz crystal oscillator in a PLL frequency synthesizer has been calibrated to a reference standard known to be accurate to 5 ppm. The oscillator is guaranteed to drift no more than 10 ppm per month. A year later, what are the maximum and minimum frequencies that the oscillator could be producing?
10.00125 MHz, 9.99875 MHz
20.0153 MHz, 75.265 MHz
10.125 MHz, 9.8875 MHz
15.00145 MHz, 10.1257 MHz

10.00125 MHz, 9.99875 MHz

Skin effect is classified as which of the following types of loss?
Induction
Copper
Voltage
Dielectric

Copper

Using Carson's rule, what is the bandwidth of an FM signal with 5 kHz maximum frequency deviation and 2.5 kHz maximum modulating frequency?
35 kHz
10 kHz
20 kHz
15 kHz

15 kHz

Distributed constants in a transmission line are distributed in which of the following ways?
Between ground and any single point on the line
According to the cross-sectional area of the line
According to the thickness of the line
Along the length of the line

Along the length of the line

Determine the power savings in percent when the carrier is suppressed in an AM signal modulated to 80%.
96.52%
75.76 %
83.33%
77.75%

75.76 %

Calculate the aperture-to-medium coupling loss for two 30-ft antennas, one at each end of the path, with a 2ᵒ scatter angle and a 900-MHz operating frequency.
3.67 dB
3.18 dB
5.37 dB
5.65 dB

3.67 dB