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Subel. L15
66 questions
Subelement L15

Antennas.

Section L15

What term describes a method used to match a high-impedance transmission line to a lower impedance antenna by connecting the line to the driven element in two places, spaced a fraction of a wavelength on each side of the driven element centre?

  • The omega match
  • The stub match
  • Correct Answer
    The T match
  • The gamma match

Gamma match: an unbalanced feed system, the coaxial braid attaches to the centre of the radiating element, the centre conductor connects via a series capacitor further along the radiating element. This second connection is done with an adjustable rod parallel to the radiating element. T match: a balanced feed system, can be thought as two mirrored gamma matches, the feed line is brought via conductors parallel to the radiating element at points further along the element. A Matching Stub is a short section of line, open or shorted, connected across the transmission line at a specific distance from the antenna feedpoint.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

What term describes an unbalanced feed system in which the driven element of an antenna is fed both at the centre and a fraction of a wavelength to one side of centre?

  • The stub match
  • The T match
  • Correct Answer
    The gamma match
  • The omega match

Gamma match: an unbalanced feed system, the coaxial braid attaches to the centre of the radiating element, the centre conductor connects via a series capacitor further along the radiating element. This second connection is done with an adjustable rod parallel to the radiating element. T match: a balanced feed system, can be thought as two mirrored gamma matches, the feed line is brought via conductors parallel to the radiating element at points further along the element. A Matching Stub is a short section of line, open or shorted, connected across the transmission line at a specific distance from the antenna feedpoint.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

What term describes a method of antenna impedance matching that uses a short section of transmission line connected to the antenna transmission line near the antenna and perpendicular to the transmission line?

  • Correct Answer
    The stub match
  • The omega match
  • The delta match
  • The gamma match

Gamma match: an unbalanced feed system, the coaxial braid attaches to the centre of the radiating element, the centre conductor connects via a series capacitor further along the radiating element. This second connection is done with an adjustable rod parallel to the radiating element. T match: a balanced feed system, can be thought as two mirrored gamma matches, the feed line is brought via conductors parallel to the radiating element at points further along the element. A Matching Stub is a short section of line, open or shorted, connected across the transmission line at a specific distance from the antenna feedpoint.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

Assuming a velocity factor of 0.66 what would be the physical length of a typical coaxial stub that is electrically one quarter wavelength long at 14.1 MHz?

  • 2.33 metres (7.64 feet)
  • 0.25 metre (0.82 foot)
  • Correct Answer
    3.51 metres (11.5 feet)
  • 20 metres (65.6 feet)

An electrical quarter wavelength can be computed in metres as one fourth of 300 divided by frequency in megahertz. The physical length equals the electrical length times the Velocity Factor. In this example, 300 divided by 14.1 divided by 4 times 0.66 = 3.51 metre.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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The driven element of a Yagi antenna is connected to a coaxial transmission line. The coax braid is connected to the centre of the driven element and the centre conductor is connected to a variable capacitor in series with an adjustable mechanical arrangement on one side of the driven element. The type of matching is:

  • zeta match
  • Correct Answer
    gamma match
  • lambda match
  • T match

Gamma match: an unbalanced feed system, the coaxial braid attaches to the centre of the radiating element, the centre conductor connects via a series capacitor further along the radiating element. This second connection is done with an adjustable rod parallel to the radiating element. T match: a balanced feed system, can be thought as two mirrored gamma matches, the feed line is brought via conductors parallel to the radiating element at points further along the element. A Matching Stub is a short section of line, open or shorted, connected across the transmission line at a specific distance from the antenna feedpoint.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

A quarter-wave stub, for use at 15 MHz, is made from a coaxial cable having a velocity factor of 0.8. Its physical length will be:

  • Correct Answer
    4 m (13.1 ft)
  • 12 m (39.4 ft)
  • 8 m (26.2 ft)
  • 7.5 m (24.6 ft)

An electrical quarter wavelength can be computed in metres as one fourth of 300 divided by frequency in megahertz. The physical length equals the electrical length times the Velocity Factor. In this example, 300 divided by 15 divided by 4 times 0.80 = 4 metres.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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The matching of a driven element with a single adjustable mechanical and capacitive arrangement is descriptive of:

  • a "T" match
  • an "omega" match
  • a "Y" match
  • Correct Answer
    a "gamma" match

Gamma match: an unbalanced feed system, the coaxial braid attaches to the centre of the radiating element, the centre conductor connects via a series capacitor further along the radiating element. This second connection is done with an adjustable rod parallel to the radiating element. T match: a balanced feed system, can be thought as two mirrored gamma matches, the feed line is brought via conductors parallel to the radiating element at points further along the element. A Matching Stub is a short section of line, open or shorted, connected across the transmission line at a specific distance from the antenna feedpoint.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

A Yagi antenna uses a gamma match. The coaxial braid connects to:

  • the adjustable gamma rod
  • the centre of the reflector
  • Correct Answer
    the centre of the driven element
  • the variable capacitor

Gamma match: an unbalanced feed system, the coaxial braid attaches to the centre of the radiating element, the centre conductor connects via a series capacitor further along the radiating element. This second connection is done with an adjustable rod parallel to the radiating element. T match: a balanced feed system, can be thought as two mirrored gamma matches, the feed line is brought via conductors parallel to the radiating element at points further along the element. A Matching Stub is a short section of line, open or shorted, connected across the transmission line at a specific distance from the antenna feedpoint.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

A Yagi antenna uses a gamma match. The centre of the driven element connects to:

  • the adjustable gamma rod
  • a variable capacitor
  • Correct Answer
    the coaxial line braid
  • the coaxial line centre conductor

Gamma match: an unbalanced feed system, the coaxial braid attaches to the centre of the radiating element, the centre conductor connects via a series capacitor further along the radiating element. This second connection is done with an adjustable rod parallel to the radiating element. T match: a balanced feed system, can be thought as two mirrored gamma matches, the feed line is brought via conductors parallel to the radiating element at points further along the element. A Matching Stub is a short section of line, open or shorted, connected across the transmission line at a specific distance from the antenna feedpoint.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

A Yagi antenna uses a gamma match. The adjustable gamma rod connects to:

  • an adjustable point on the reflector
  • the centre of the driven element
  • Correct Answer
    the variable capacitor
  • the coaxial line centre conductor

Gamma match: an unbalanced feed system, the coaxial braid attaches to the centre of the radiating element, the centre conductor connects via a series capacitor further along the radiating element. This second connection is done with an adjustable rod parallel to the radiating element. T match: a balanced feed system, can be thought as two mirrored gamma matches, the feed line is brought via conductors parallel to the radiating element at points further along the element. A Matching Stub is a short section of line, open or shorted, connected across the transmission line at a specific distance from the antenna feedpoint.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

A Yagi antenna uses a gamma match. The variable capacitor connects to the:

  • Correct Answer
    adjustable gamma rod
  • an adjustable point on the director
  • center of the driven element
  • coaxial line braid

Gamma match: an unbalanced feed system, the coaxial braid attaches to the centre of the radiating element, the centre conductor connects via a series capacitor further along the radiating element. This second connection is done with an adjustable rod parallel to the radiating element. T match: a balanced feed system, can be thought as two mirrored gamma matches, the feed line is brought via conductors parallel to the radiating element at points further along the element. A Matching Stub is a short section of line, open or shorted, connected across the transmission line at a specific distance from the antenna feedpoint.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

In a half-wave dipole, the distribution of _______ is highest at each end.

  • current
  • inductance
  • capacitance
  • Correct Answer
    voltage

On a centre-fed resonant half-wave dipole, current is high and voltage low at the feedpoint, the ends exhibit high voltage and low current. Low voltage and high current at the centre make for low impedance ( Z = E divided by I ).

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

In a half-wave dipole, the distribution of _______ is lowest at each end.

  • capacitance
  • Correct Answer
    current
  • voltage
  • inductance

On a centre-fed resonant half-wave dipole, current is high and voltage low at the feedpoint, the ends exhibit high voltage and low current. Low voltage and high current at the centre make for low impedance ( Z = E divided by I ).

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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The feed point in a centre-fed half-wave antenna is at the point of:

  • minimum voltage and current
  • maximum voltage
  • Correct Answer
    maximum current
  • minimum current

On a centre-fed resonant half-wave dipole, current is high and voltage low at the feedpoint, the ends exhibit high voltage and low current. Low voltage and high current at the centre make for low impedance ( Z = E divided by I ).

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

In a half-wave dipole, the lowest distribution of _________ occurs at the middle.

  • Correct Answer
    voltage
  • capacity
  • inductance
  • current

On a centre-fed resonant half-wave dipole, current is high and voltage low at the feedpoint, the ends exhibit high voltage and low current. Low voltage and high current at the centre make for low impedance ( Z = E divided by I ).

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

In a half-wave dipole, the highest distribution of ________ occurs at the middle.

  • Correct Answer
    current
  • inductance
  • voltage
  • capacity

On a centre-fed resonant half-wave dipole, current is high and voltage low at the feedpoint, the ends exhibit high voltage and low current. Low voltage and high current at the centre make for low impedance ( Z = E divided by I ).

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

A half-wave dipole antenna is normally fed at the point where:

  • the voltage is maximum
  • the resistance is maximum
  • the antenna is resonant
  • Correct Answer
    the current is maximum

On a centre-fed resonant half-wave dipole, current is high and voltage low at the feedpoint, the ends exhibit high voltage and low current. Low voltage and high current at the centre make for low impedance ( Z = E divided by I ).

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

At the ends of a half-wave dipole:

  • voltage and current are both low
  • voltage is low and current is high
  • Correct Answer
    voltage is high and current is low
  • voltage and current are both high

On a centre-fed resonant half-wave dipole, current is high and voltage low at the feedpoint, the ends exhibit high voltage and low current. Low voltage and high current at the centre make for low impedance ( Z = E divided by I ).

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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The impedance of a half-wave antenna at its centre is low, because at this point:

  • voltage and current are both low
  • voltage is high and current is low
  • Correct Answer
    voltage is low and current is high
  • voltage and current are both high

On a centre-fed resonant half-wave dipole, current is high and voltage low at the feedpoint, the ends exhibit high voltage and low current. Low voltage and high current at the centre make for low impedance ( Z = E divided by I ).

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

In a half-wave dipole, where does minimum voltage occur?

  • Both ends
  • Correct Answer
    The centre
  • At the right end
  • It is equal at all points

On a centre-fed resonant half-wave dipole, current is high and voltage low at the feedpoint, the ends exhibit high voltage and low current. Low voltage and high current at the centre make for low impedance ( Z = E divided by I ).

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

In a half-wave dipole, where does the minimum current occur?

  • At the centre
  • It is equal at all points
  • At the right end
  • Correct Answer
    At both ends

On a centre-fed resonant half-wave dipole, current is high and voltage low at the feedpoint, the ends exhibit high voltage and low current. Low voltage and high current at the centre make for low impedance ( Z = E divided by I ).

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

In a half-wave dipole, where does the minimum impedance occur?

  • At both ends
  • Correct Answer
    At the centre
  • It is the same at all points
  • At the right end

On a centre-fed resonant half-wave dipole, current is high and voltage low at the feedpoint, the ends exhibit high voltage and low current. Low voltage and high current at the centre make for low impedance ( Z = E divided by I ).

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

What is meant by circularly polarized electromagnetic waves?

  • Waves with an electric field bent into circular shape
  • Waves that circle the earth
  • Waves produced by a circular loop antenna
  • Correct Answer
    Waves with a rotating electric field

The polarization of an electromagnetic radio wave corresponds to the position of the electrical field with respect to the surface of the Earth: horizontal when the E field is parallel to ground and vertical when perpendicular to ground. The magnetic field is at 90 degrees (perpendicular) to the electrical field. Dipoles and Yagis are linearly polarized antennas (i.e., the electrical field has a constant orientation). Circular polarization, where the polarization rotates, can be obtained from helical beam antennas or with crossed linear antennas fed with the correct phase difference. "Sense" refers to the direction of the rotation: clockwise polarization for a receding wave is termed right-hand.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What type of polarization is produced by crossed dipoles fed 90 degrees out of phase?

  • Correct Answer
    Circular polarization
  • Cross-polarization
  • Perpendicular polarization
  • None of the other answers, the two fields cancel out

Crossed dipoles fed 90 degrees out of phase are the active elements of a turnstile antenna and produce circular polarization. The turnstile antenna is used for satellite communications.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Which of these antennas does not produce circular polarization?

  • Lindenblad antenna
  • Axial-mode helical antenna
  • Correct Answer
    Loaded helical-wound antenna
  • Crossed dipoles fed 90 degrees out of phase

Key word: NOT. Antennas featuring a fine wire wound around a shaft (e.g., HF mobile antennas) are "loaded helical-wound antennas"; these produce a linear polarization, i.e., vertical or horizontal depending on their positions relative to ground. The axial-mode helical antenna, with its corkscrew look, is used in satellite work and produces circular polarization.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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On VHF/UHF frequencies, Doppler shift becomes of consequence on which type of communication?

  • Simplex line-of-sight contact between hand-held transceivers
  • Contact with terrestrial mobile stations
  • Correct Answer
    Contact via satellite
  • Contact through a hilltop repeater

"Doppler shift: the change in frequency of a received signal due to the motion of the satellite. This requires adjustment of the transmit or receive frequency, with the common practice being to change the higher of the two frequencies in use" (http://www.amsat.org/). Low Earth orbiting satellites travel at speeds around 28 000 km/h. The higher the operating frequency, the higher the possible shift: for example, +/- 600 Hz on 10 m, +/- 3 kHz on 2 m and +/- 9 kHz on 70 cm.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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For VHF and UHF signals over a fixed path, what extra loss can be expected when linearly-polarized antennas are crossed-polarized (90 degrees)?

  • 6 dB
  • 10 dB
  • Correct Answer
    20 dB or more
  • 3 dB

"A loss in signal strength of 20 dB or more can be expected with cross-polarization so it is important to use antennas with the same polarization as the stations with which you expect to communicate." (ARRL Antenna Book, 22nd ed., section 21.10.5 Polarization)

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Which of the following is NOT a valid parabolic dish illumination arrangement?

  • Offset feed
  • Cassegrain
  • Correct Answer
    Newtonian
  • Front feed

Key word: NOT. Front feed (also known as focal feed or axial feed): circular reflector, the feed is centered in front of the reflector, very common on larger dish antennas. Offset feed (also known as off-axis): elliptical reflector, the feed is off to one side, out of the path of the radio waves, typical of domestic satellite receiving antennas. Cassegrain (based on the Cassegrain telescope): the feed is behind the dish and relies on a small convex secondary reflector in front of the dish. Newtonian: a bogus answer, valid for telescopes.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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A parabolic antenna is very efficient because:

  • a horn-type radiator can be used to trap the received energy
  • Correct Answer
    all the received energy is focused to a point where the pick-up antenna is located
  • a dipole antenna can be used to pick up the received energy
  • no impedance matching is required

A parabolic reflector dish provides significant gain because energy striking any point of the parabola is reflected to the focal point with the correct phase. On transmit, the inverse process takes place: all energy directed at the parabola from the feed antenna is reflected forward with the correct phase. High gain antennas used on UHF or microwave frequencies present a real risk to living tissues: never stand in front of a transmitting antenna.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

A helical-beam antenna with right-hand polarization will best receive signals with:

  • left-hand polarization
  • vertical polarization only
  • horizontal polarization
  • Correct Answer
    right-hand polarization

The helical beam antenna is circularly polarized. Although it will respond to horizontally or vertically polarized waves, the full gain of the antenna can only be realized with a circularly polarized wave of the same "sense".

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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One antenna which will respond simultaneously to vertically- and horizontally-polarized signals is the:

  • Correct Answer
    helical-beam antenna
  • folded dipole antenna
  • ground-plane antenna
  • quad antenna

The dipole, ground-plane and quad are all linearly polarized and thus respond optimally to waves polarized in a single given direction, horizontal or vertical as the case may be. Unless proper alignment is assured, a significant loss is incurred. The helical beam antenna is circularly polarized, it can deal with the rotating fields of a wave with circular polarization. Consequently, it can deal with any single polarization at any given angle.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

In amateur work, what is the surface error upper limit you should try not to exceed on a parabolic reflector?

  • 0.25 lambda
  • 5 mm (0.2 in) regardless of frequency
  • 1% of the diameter
  • Correct Answer
    0.1 lambda

"Surface errors should not exceed 1/8 lambda in amateur operation. At 430 MHz, 1/8 lambda is 3.4 inches [8.6 cm], but at 10 GHz, it is 0.1476 inch [3.7 mm]! (...) Mesh can be used for the reflector surface to reduce weight and wind loading, but hole size should be less than 1/12 lambda." (ARRL Antenna Book 22nd ed., sect. 15.6.2)

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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You want to convert a surplus parabolic dish for amateur radio use, the gain of this antenna depends on:

  • the material composition of the dish
  • Correct Answer
    the diameter of the antenna in wavelengths
  • the polarization of the feed device illuminating it
  • the focal length of the antenna

Gain is primarily affected by the antenna aperture (reflector area) to wavelength ratio.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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A transmitter has an output of 100 watts. The cable and connectors have a composite loss of 3 dB, and the antenna has a gain of 6 dBd. What is the Effective Radiated Power?

  • 350 watts
  • 400 watts
  • 300 watts
  • Correct Answer
    200 watts

Effective Radiated Power (ERP) equals transmitter power minus line losses plus antenna gain. In this example, minus 3 dB plus 6 dB yields a net increase of 3 dB or twice the power.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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As standing wave ratio rises, so does the loss in the transmission line. This is caused by:

  • high antenna currents
  • high antenna voltage
  • leakage to ground through the dielectric
  • Correct Answer
    dielectric and conductor heat losses

Voltage peaks on the standing wave increase losses through the dielectric ( P = E squared divided by R ), current peaks on the standing wave increase conductor losses ( P = I squared times R ).

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What is the Effective Radiated Power of an amateur transmitter, if the transmitter output power is 200 watts, the transmission line loss is 5 watts, and the antenna power gain is 3 dBd?

  • Correct Answer
    390 watts
  • 197 watts
  • 228 watts
  • 178 watts

Effective Radiated Power (ERP) equals transmitter power minus line losses plus antenna gain. In this example, minus 5 watts plus 3 dB yields a net increase of 3 dB or twice the remaining power of 195 watts.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Effective Radiated Power means the:

  • Correct Answer
    transmitter output power, minus line losses, plus antenna gain relative to a dipole
  • power supplied to the antenna before the modulation of the carrier
  • power supplied to the transmission line plus antenna gain
  • ratio of signal output power to signal input power

Effective Radiated Power (ERP) equals transmitter power minus line losses plus antenna gain.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

A transmitter has an output power of 200 watts. The coaxial and connector losses are 3 dB in total, and the antenna gain is 9 dBd. What is the approximate Effective Radiated Power of this system?

  • Correct Answer
    800 watts
  • 3200 watts
  • 1600 watts
  • 400 watts

Effective Radiated Power (ERP) equals transmitter power minus line losses plus antenna gain. In this example, minus 3 dB plus 9 dB yields a net increase of 6 dB or four times the power.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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A transmitter has a power output of 100 watts. There is a loss of 1.30 dB in the transmission line, a loss of 0.2 dB through the antenna tuner, and a gain of 4.50 dBd in the antenna. The Effective Radiated Power (ERP) is:

  • 800 watts
  • 400 watts
  • 100 watts
  • Correct Answer
    200 watts

Effective Radiated Power (ERP) equals transmitter power minus line losses plus antenna gain. In this example, minus 1.5 dB plus 4.5 dB yields a net increase of 3 dB or twice the power.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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If the overall gain of an amateur station is increased by 3 dB the ERP (Effective Radiated Power) will:

  • be cut in half
  • Correct Answer
    double
  • decrease by 3 watts
  • remain the same

Effective Radiated Power (ERP) equals transmitter power minus line losses plus antenna gain. In this example, a net gain of 3 dB yields twice the power.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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A transmitter has a power output of 125 watts. There is a loss of 0.8 dB in the transmission line, 0.2 dB in the antenna tuner, and a gain of 10 dBd in the antenna. The Effective Radiated Power (ERP) is:

  • 1250
  • 1125
  • 134
  • Correct Answer
    1000

Effective Radiated Power (ERP) equals transmitter power minus line losses plus antenna gain. In this example, minus 1 dB plus 10 dB yields a net increase of 9 dB or eight times the power.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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If a 3 dBd gain antenna is replaced with a 9 dBd gain antenna, with no other changes, the Effective Radiated Power (ERP) will increase by:

  • Correct Answer
    4
  • 6
  • 1.5
  • 2

Effective Radiated Power (ERP) equals transmitter power minus line losses plus antenna gain. In this example, an added 6 dB yields four times the power.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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A transmitter has an output of 2000 watts PEP. The transmission line, connectors and antenna tuner have a composite loss of 1 dB, and the gain from the stacked Yagi antenna is 10 dBd. What is the Effective Radiated Power (ERP) in watts PEP?

  • 2009
  • Correct Answer
    16 000
  • 18 000
  • 20 000

Effective Radiated Power (ERP) equals transmitter power minus line losses plus antenna gain. In this example, minus 1 dB plus 10 dB yields a net increase of 9 dB or eight times the power.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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A transmitter has an output of 1000 watts PEP. The coaxial cable, connectors and antenna tuner have a composite loss of 1 dB, and the antenna gain is 10 dBd. What is the Effective Radiated Power (ERP) in watts PEP?

  • Correct Answer
    8000
  • 1009
  • 10 000
  • 9000

Effective Radiated Power (ERP) equals transmitter power minus line losses plus antenna gain. In this example, minus 1 dB plus 10 dB yields a net increase of 9 dB or eight times the power.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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For a 3-element Yagi antenna with horizontally mounted elements, how does the main lobe takeoff angle vary with height above flat ground?

  • It does not vary with height
  • It depends on E-region height, not antenna height
  • Correct Answer
    It decreases with increasing height
  • It increases with increasing height

Greater antenna heights tend to lower the main radiation lobe where ground reflections end up in phase with direct radiation from the antenna.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Most simple horizontally polarized antennas do not exhibit significant directivity unless they are:

  • an eighth of a wavelength above the ground
  • a quarter wavelength above the ground
  • three-eighths of a wavelength above the ground
  • Correct Answer
    a half wavelength or more above the ground

Below one half-wavelength in antenna height, there is little point in selecting a given broadside direction: for example, choosing a north-south orientation to favour east-west radiation will not pay significant dividends for antennas close to ground.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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The plane from which ground reflections can be considered to take place, or the effective ground plane for an antenna is:

  • as much as 6 cm below ground depending upon soil conditions
  • as much as a meter above ground
  • at ground level exactly
  • Correct Answer
    several centimeters to as much as 2 meters below ground, depending upon soil conditions

Current penetration around an antenna depends first on frequency and then on soil conductivity and dielectric constant. At HF frequencies over salt water, penetration ranges from 5 to 18 centimetres. Over poor ground, penetration can exceed 10 metres.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Why is a ground-mounted vertical quarter-wave antenna in reasonably open surroundings better for long distance contacts than a half-wave dipole at a quarter wavelength above ground?

  • It has an omnidirectional characteristic
  • It uses vertical polarization
  • Correct Answer
    The vertical radiation angle is lower
  • The radiation resistance is lower

Key words: DIPOLE AT A QUARTER WAVELENGTH HEIGHT. At heights below three eights of a wavelength, ground reflections cause horizontal dipoles to direct more energy straight up. At a height of one half-wavelength, radiation at 90 degrees is minimized and two lobes form at 30 degrees. In this comparison, the ground-mounted vertical undoubtedly exhibits a lower radiation angle as it cannot possibly radiate upwards.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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When a half-wave dipole antenna is installed one-half wavelength above ground, the:

  • radiation pattern is unaffected
  • Correct Answer
    vertical or upward radiation is effectively cancelled
  • radiation pattern changes to produce side lobes at 15 and 50 degrees
  • side lobe radiation is cancelled

At heights below three eights of a wavelength, ground reflections cause horizontal dipoles to direct more energy straight up. At a height of one half-wavelength, radiation at 90 degrees is minimized and two lobes form at 30 degrees.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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How does antenna height affect the horizontal (azimuthal) radiation pattern of a horizontal dipole HF antenna?

  • Correct Answer
    If the antenna is less than one-half wavelength high, reflected radio waves from the ground significantly distort the pattern
  • Antenna height has no effect on the pattern
  • If the antenna is less than one-half wavelength high, radiation off the ends of the wire is eliminated
  • If the antenna is too high, the pattern becomes unpredictable

Below one half-wavelength in antenna height, there is little point in selecting a given broadside direction: for example, choosing a north-south orientation to favour east-west radiation will not pay significant dividends for antennas close to ground.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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For long distance propagation, the vertical radiation angle of the energy from the antenna should be:

  • more than 30 degrees but less than 45 degrees
  • Correct Answer
    less than 30 degrees
  • more than 45 degrees but less than 90 degrees
  • 90 degrees

Depending on band (for example, 10, 15 and 20 metre) and distance, preferred radiation angles range from 1 to 25 degrees for long distance communication. A low radiation angle permits hitting the ionosphere at a greater distance for longer skip distances.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Greater distance can be covered with multiple-hop transmissions by decreasing the:

  • power applied to the antenna
  • main height of the antenna
  • length of the antenna
  • Correct Answer
    vertical radiation angle of the antenna

Depending on band (for example, 10, 15 and 20 metre) and distance, preferred radiation angles range from 1 to 25 degrees for long distance communication. A low radiation angle permits hitting the ionosphere at a greater distance for longer skip distances.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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The impedance at the centre of a dipole antenna more than 3 wavelengths above ground would be nearest to:

  • 300 ohms
  • 600 ohms
  • Correct Answer
    75 ohms
  • 25 ohms

The impedance of a dipole in free space is known as 73 ohms. Below a height of a half-wavelength, impedance is greatly affected by ground proximity. At one wavelength and up, impedance begins to track the free-space value more closely.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Why can a horizontal antenna closer to ground be advantageous for close range communications on lower HF bands?

  • Correct Answer
    The ground tends to act as a reflector
  • Lower antenna noise temperature
  • Low radiation angle for closer distances
  • The radiation resistance is higher

Near-Vertical Incidence Sky wave (NVIS) -- "The use of very low dipole antennas that radiate at very high elevation angles has become popular in emergency communications ("emcomm") systems. This works at low frequencies (7 MHz and below) that are lower than the ionosphere's critical frequency -- the highest frequency for which a signal traveling vertically will be reflected." (ARRL Handbook, 2012 ed., 21.2.12 NVIS Antennas)

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Which antenna system and operating frequency are most suitable for Near Vertical Incidence (NVIS) communications?

  • A horizontal antenna at a height of half a wavelength and an operating frequency at the optimum working frequency
  • A vertical antenna and a frequency below the maximum usable frequency
  • A vertical antenna and a frequency above the lowest usable frequency
  • Correct Answer
    A horizontal antenna less than 1/4 wavelength above ground and a frequency below the current critical frequency

Near-Vertical Incidence Sky wave (NVIS) -- "The use of very low dipole antennas that radiate at very high elevation angles has become popular in emergency communications ("emcomm") systems. This works at low frequencies (7 MHz and below) that are lower than the ionosphere's critical frequency -- the highest frequency for which a signal traveling vertically will be reflected." (ARRL Handbook, 2012 ed., 21.2.12 NVIS Antennas)

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What is meant by the radiation resistance of an antenna?

  • Correct Answer
    The equivalent resistance that would dissipate the same amount of power as that radiated from an antenna
  • The resistance in the atmosphere that an antenna must overcome to be able to radiate a signal
  • The specific impedance of an antenna
  • The combined losses of the antenna elements and transmission line

The power delivered to an antenna can be transformed in two ways: some of it is lost through heat and dielectric losses, the rest is radiated. The part that is radiated can be imagined to have "disappeared" into a virtual resistance. Radiation Resistance is defined as an equivalent resistance that would have dissipated all the power radiated. The dimensions of the radiating element, particularly its length, and its immediate environment, the proximity to ground for instance, affect radiation resistance. Except for electrically short antennas, radiation resistance makes up most of the antenna impedance. Antenna efficiency in percentage can be computed as Radiation Resistance over total resistance times 100.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Why would one need to know the radiation resistance of an antenna?

  • Correct Answer
    To match impedances for maximum power transfer
  • To measure the near-field radiation density from a transmitting antenna
  • To calculate the front-to-side ratio of the antenna
  • To calculate the front-to-back ratio of the antenna

The power delivered to an antenna can be transformed in two ways: some of it is lost through heat and dielectric losses, the rest is radiated. The part that is radiated can be imagined to have "disappeared" into a virtual resistance. Radiation Resistance is defined as an equivalent resistance that would have dissipated all the power radiated. The dimensions of the radiating element, particularly its length, and its immediate environment, the proximity to ground for instance, affect radiation resistance. Except for electrically short antennas, radiation resistance makes up most of the antenna impedance. Antenna efficiency in percentage can be computed as Radiation Resistance over total resistance times 100.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What factors determine the radiation resistance of an antenna?

  • Sunspot activity and time of day
  • It is a physical constant and is the same for all antennas
  • Correct Answer
    Antenna location with respect to nearby objects and the conductors length/diameter ratio
  • Transmission line length and antenna height

The power delivered to an antenna can be transformed in two ways: some of it is lost through heat and dielectric losses, the rest is radiated. The part that is radiated can be imagined to have "disappeared" into a virtual resistance. Radiation Resistance is defined as an equivalent resistance that would have dissipated all the power radiated. The dimensions of the radiating element, particularly its length, and its immediate environment, the proximity to ground for instance, affect radiation resistance. Except for electrically short antennas, radiation resistance makes up most of the antenna impedance. Antenna efficiency in percentage can be computed as Radiation Resistance over total resistance times 100.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What is the term for the ratio of the radiation resistance of an antenna to the total resistance of the system?

  • Correct Answer
    Antenna efficiency
  • Beamwidth
  • Effective Radiated Power
  • Radiation conversion loss

The power delivered to an antenna can be transformed in two ways: some of it is lost through heat and dielectric losses, the rest is radiated. The part that is radiated can be imagined to have "disappeared" into a virtual resistance. Radiation Resistance is defined as an equivalent resistance that would have dissipated all the power radiated. The dimensions of the radiating element, particularly its length, and its immediate environment, the proximity to ground for instance, affect radiation resistance. Except for electrically short antennas, radiation resistance makes up most of the antenna impedance. Antenna efficiency in percentage can be computed as Radiation Resistance over total resistance times 100.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What is included in the total resistance of an antenna system?

  • Radiation resistance plus transmission resistance
  • Transmission line resistance plus radiation resistance
  • Radiation resistance plus space impedance
  • Correct Answer
    Radiation resistance plus ohmic resistance

The power delivered to an antenna can be transformed in two ways: some of it is lost through heat and dielectric losses, the rest is radiated. The part that is radiated can be imagined to have "disappeared" into a virtual resistance. Radiation Resistance is defined as an equivalent resistance that would have dissipated all the power radiated. The dimensions of the radiating element, particularly its length, and its immediate environment, the proximity to ground for instance, affect radiation resistance. Except for electrically short antennas, radiation resistance makes up most of the antenna impedance. Antenna efficiency in percentage can be computed as Radiation Resistance over total resistance times 100.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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How can the approximate beamwidth of a beam antenna be determined?

  • Measure the ratio of the signal strengths of the radiated power lobes from the front and side of the antenna
  • Measure the ratio of the signal strengths of the radiated power lobes from the front and rear of the antenna
  • Correct Answer
    Note the two points where the signal strength is down 3 dB from the maximum signal point and compute the angular difference
  • Draw two imaginary lines through the ends of the elements and measure the angle between the lines

Beamwidth is defined as the width in degrees over which the major lobe is within 3 dB of maximum gain, this is equally described as the angle between the half-power points.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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How is antenna percent efficiency calculated?

  • (radiation resistance / transmission resistance) x 100
  • (total resistance / radiation resistance) x 100
  • (effective radiated power / transmitter output) x 100
  • Correct Answer
    (radiation resistance / total resistance) x 100

The power delivered to an antenna can be transformed in two ways: some of it is lost through heat and dielectric losses, the rest is radiated. The part that is radiated can be imagined to have "disappeared" into a virtual resistance. Radiation Resistance is defined as an equivalent resistance that would have dissipated all the power radiated. The dimensions of the radiating element, particularly its length, and its immediate environment, the proximity to ground for instance, affect radiation resistance. Except for electrically short antennas, radiation resistance makes up most of the antenna impedance. Antenna efficiency in percentage can be computed as Radiation Resistance over total resistance times 100.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What is the term used for an equivalent resistance which would dissipate the same amount of energy as that radiated from an antenna?

  • j factor
  • Antenna resistance
  • K factor
  • Correct Answer
    Radiation resistance

The power delivered to an antenna can be transformed in two ways: some of it is lost through heat and dielectric losses, the rest is radiated. The part that is radiated can be imagined to have "disappeared" into a virtual resistance. Radiation Resistance is defined as an equivalent resistance that would have dissipated all the power radiated. The dimensions of the radiating element, particularly its length, and its immediate environment, the proximity to ground for instance, affect radiation resistance. Except for electrically short antennas, radiation resistance makes up most of the antenna impedance. Antenna efficiency in percentage can be computed as Radiation Resistance over total resistance times 100.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Antenna beamwidth is the angular distance between:

  • the 3 dB power points on the first minor lobe
  • Correct Answer
    the points on the major lobe at the half-power points
  • the maximum lobe spread points on the major lobe
  • the 6 dB power points on the major lobe

Beamwidth is defined as the width in degrees over which the major lobe is within 3 dB of maximum gain, this is equally described as the angle between the half-power points.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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If the ohmic resistance of a half-wave dipole is 2 ohms, and the radiation resistance is 72 ohms, what is the antenna efficiency?

  • 72%
  • 100%
  • Correct Answer
    97.3%
  • 74%

Antenna efficiency in percentage can be computed as Radiation Resistance over total resistance times 100. In this example, 72 divided by 74 is 97.3%

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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If the ohmic resistance of a miniloop antenna is 2 milliohms and the radiation resistance is 50 milliohms, what is the antenna efficiency?

  • Correct Answer
    96.15%
  • 52%
  • 25%
  • 50%

Antenna efficiency in percentage can be computed as Radiation Resistance over total resistance times 100. In this example, 50 divided by 52 is 96.2%

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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