Friday, April 17, 2015

Extra question pool with answers. - antennas

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

Radiation resistance plus ohmic resistance.
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Which of the following describes an isotropic radiator?

A theoretical radiator used to compare other antennas

When is it useful to refer to an isotropic radiator?

When comparing the gains of directional antennas
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How much gain does a 1/2-wavelength dipole have over an isotropic radiator?

About 2.1 dB
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Which of the following antennas has no gain in any direction?
Isotropic radiator
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Which of the following describes the radiation pattern of an isotropic radiator?

A sphere with the antenna in the center
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Why would one need to know the feed point impedance of an antenna?

To match impedances for maximum power transfer
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What factors determine the radiation resistance of an antenna?

Antenna location with respect to nearby objects and the conductors' length/diameter ratio
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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?

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

Radiation resistance plus ohmic resistance.
---
What is a folded dipole antenna?
A dipole whose ends are connected by a one-half wavelength piece of wire
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What is meant by antenna gain?

The numerical ratio relating the radiated signal strength of an antenna to that of another antenna
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What is meant by antenna bandwidth?

The frequency range over which an antenna can be expected to perform well
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How can the approximate beamwidth of a beam antenna be determined?

Note the two points where the signal strength of the antenna is down 3 dB from the maximum signal point and compute the angular difference
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How is antenna efficiency calculated?

(radiation resistance / total resistance) x 100%
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How can the efficiency of an HF grounded vertical antenna be made comparable to that of a half-wave dipole antenna?

By installing a good ground radial system
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What theoretical reference antenna provides a comparison for antenna measurements?
Isotropic radiator
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How much gain does an antenna have over a 1/2-wavelength dipole when it has 6 dB gain over an isotropic radiator?

About 3.9 dB
---

Which of the following describes the directivity of an isotropic radiator?

No directivity at all
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What is meant by radiation resistance of an antenna?

The value of resistance that would dissipate the same amount of power as that radiated from an antenna.
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What determines the free-space polarization of an antenna?

The orientation of its electric field (E Field)
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In the free-space H-Field radiation pattern shown in Figure E9-1, what is the 3-dB beamwidth?

50 degrees
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In the free-space H-Field pattern shown in Figure E9-1, what is the front-to-back ratio?

18 dB
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In the free-space H-field pattern shown in Figure E9-1, what is the front-to-side ratio?

14 dB
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What information is needed to accurately evaluate the gain of an antenna?

All of these choices
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Which is NOT an important reason to evaluate a gain antenna across the whole frequency band for which it was designed?

The dielectric constant may vary significantly
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What usually occurs if a Yagi antenna is designed solely for maximum forward gain?

The feed-point impedance becomes very low
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If the boom of a Yagi antenna is lengthened and the elements are properly retuned, what usually occurs?

The gain increases
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What type of computer program is commonly used for modeling antennas?

Method of Moments
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What is the principle of a Method of Moments analysis?

A wire is modeled as a series of segments, each having a distinct value of current
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What is the radiation pattern of two 1/4-wavelength vertical antennas spaced 1/2-wavelength apart and fed 180 degrees out of phase?
Figure-8 end-fire in line with the antennas
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What is the radiation pattern of two 1/4-wavelength vertical antennas spaced 1/4-wavelength apart and fed 90 degrees out of phase?

Unidirectional cardioid
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What is the radiation pattern of two 1/4-wavelength vertical antennas spaced 1/2-wavelength apart and fed in phase?

Figure-8 broadside to the antennas
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What is the radiation pattern of two 1/4-wavelength vertical antennas spaced 1/4-wavelength apart and fed 180 degrees out of phase?

Figure-8 end-fire in line with the antennas
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What is the radiation pattern for two 1/4-wavelength vertical antennas spaced 1/8-wavelength apart and fed 180 degrees out of phase?

Figure-8 end-fire in line with the antennas
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What is the radiation pattern for two 1/4-wavelength vertical antennas spaced 1/4-wavelength apart and fed in phase?

Elliptical
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Which of the following is the best description of a resonant rhombic antenna?

Bidirectional; four-sided, each side approximately one wavelength long; open at the end opposite the transmission line connection
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What are the advantages of a terminated rhombic antenna?
Wide frequency range, high gain and high front-to-back ratio
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What are the disadvantages of a terminated rhombic antenna for the HF bands?

A large area and four sturdy supports for proper installation
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What is the effect of a terminating resistor on a rhombic antenna?

It changes the radiation pattern from essentially bidirectional to essentially unidirectional
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What type of antenna pattern over real ground is shown in Figure E9-2?
Elevation pattern
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In the H field antenna radiation pattern shown in Figure E9-2, what is the elevation angle of the peak response?

7.5 degrees
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In the H field antenna radiation pattern shown in Figure E9-2, what is the front-to-back ratio?

28 dB
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In the H field antenna radiation pattern shown in Figure E9-2, how many elevation lobes appear in the forward direction?
4
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How is the far-field elevation pattern of a vertically polarized antenna affected by being mounted over seawater versus rocky ground?

The low-angle radiation increases
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If only a modest on-ground radial system can be used with an eighth-wavelength-high, inductively loaded vertical antenna, what would be the best compromise to minimize near-field losses?

A wire-mesh screen at the antenna base, an eighth-wavelength square
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What is one characteristic of a Beverage antenna?

For best performance it should be longer than one wavelength
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How would the electric field be oriented for a Yagi with three elements mounted parallel to the ground?

Horizontally
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What strongly affects the shape of the far-field, low-angle elevation pattern of a vertically polarized antenna?

The conductivity and dielectric constant of the soil
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Why are elevated-radial counterpoises popular with vertically polarized antennas?

They reduce the near-field ground losses, compared to on-ground radial systems using more radials
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What is a terminated rhombic antenna?

A unidirectional antenna terminated in a resistance equal to its characteristic impedance
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What factors determine the receiving antenna gain required at an amateur satellite station in earth operation?

Height, transmitter power and antennas of satellite
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What factors determine the EIRP required by an amateur satellite station in earth operation?

Satellite antennas and height, satellite receiver sensitivity
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What is the approximate beamwidth of a symmetrical pattern antenna with a gain of 20 dB as compared to an isotropic radiator?

20 degrees
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How does the gain of a parabolic dish antenna change when the operating frequency is doubled?

Gain increases 6 dB
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How is circular polarization produced using linearly polarized antennas?

Arrange two Yagis perpendicular to each other, with the driven elements in the same plane, fed 90 degrees out of phase
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How does the beamwidth of an antenna vary as the gain is increased?

It decreases
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Why does a satellite communications antenna system for earth operation need to have rotators for both azimuth and elevation control?

In order to track the satellite as it orbits the earth
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For a shortened vertical antenna, where should a loading coil be placed to minimize losses and produce the most effective performance?

Near the center of the vertical radiator
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Why should an HF mobile antenna loading coil have a high ratio of reactance to resistance?

To minimize losses
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What is a disadvantage of using a trap antenna?

It will radiate harmonics
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How must the driven element in a 3-element Yagi be tuned to use a hairpin matching system?

The driven element reactance is capacitive
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What is the equivalent lumped-constant network for a hairpin matching system on a 3-element Yagi?

L network
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What happens to the bandwidth of an antenna as it is shortened through the use of loading coils?

It is decreased
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What is an advantage of using top loading in a shortened HF vertical antenna?

Improved radiation efficiency
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What is the approximate input terminal impedance at the center of a folded dipole antenna?

300 ohms
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Why is a loading coil often used with an HF mobile antenna?

To tune out the capacitive reactance
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What is an advantage of using a trap antenna?

It may be used for multi-band operation
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What happens at the base feed-point of a fixed length HF mobile antenna as the frequency of operation is lowered?

The resistance decreases and the capacitive reactance increases
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What is the beamwidth of a symmetrical pattern antenna with a gain of 30 dB as compared to an isotropic radiator?

6.4 degrees
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What is the beamwidth of a symmetrical pattern antenna with a gain of 15 dB as compared to an isotropic radiator?

36 degrees
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What is the beamwidth of a symmetrical pattern antenna with a gain of 12 dB as compared to an isotropic radiator?

51 degrees
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What system matches 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 each side of element center?

The delta matching system
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: What system matches an unbalanced feed line to an antenna by feeding the driven element both at the center of the element and at a fraction of a wavelength to one side of center?

The gamma matching system
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What impedance matching system uses a short perpendicular section of transmission line connected to the feed line near the antenna?

The stub matching system
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What should be the approximate capacitance of the resonating capacitor in a gamma matching circuit on a Yagi beam antenna for the 20-meter band?

140 pF
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What should be the approximate capacitance of the resonating capacitor in a gamma matching circuit on a Yagi beam antenna for the 10-meter band?

70 pF
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What is the velocity factor of a transmission line?

The velocity of the wave on the transmission line divided by the velocity of light in a vacuum
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What determines the velocity factor in a transmission line?

Dielectrics in the line
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Why is the physical length of a coaxial cable transmission line shorter than its electrical length?

RF energy moves slower along the coaxial cable
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What is the typical velocity factor for a coaxial cable with polyethylene dielectric?

0.66
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What would be the physical length of a typical coaxial transmission line that is electrically one-quarter wavelength long at 14.1 MHz? (Assume a velocity factor of 0.66.)

3.5 meters
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What is the physical length of a parallel conductor feed line that is electrically one-half wavelength long at 14.10 MHz? (Assume a velocity factor of 0.95.)

10 meters
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What parameter best describes the interactions at the load end of a mismatched transmission line?

Reflection coefficient
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Which of the following measurements describes a mismatched transmission line?

An SWR greater than 1:1
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What characteristic will 450-ohm ladder line have at 50 MHz, as compared to 0.195-inch-diameter coaxial cable (such as RG-58)?

Lower loss in dB/100 feet
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What is the term for the ratio of the actual velocity at which a signal travels through a transmission line to the speed of light in a vacuum?

Velocity factor
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What would be the physical length of a typical coaxial transmission line that is electrically one-quarter wavelength long at 7.2 MHz? (Assume a velocity factor of 0.66.)

6.9 meters
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What kind of impedance does a 1/8-wavelength transmission line present to a generator when the line is shorted at the far end?

An inductive reactance
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What kind of impedance does a 1/8-wavelength transmission line present to a generator when the line is open at the far end?

A capacitive reactance
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What kind of impedance does a 1/4-wavelength transmission line present to a generator when the line is open at the far end?

A very low impedance
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What kind of impedance does a 1/4-wavelength transmission line present to a generator when the line is shorted at the far end?

A very high impedance
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What kind of impedance does a 1/2-wavelength transmission line present to a generator when the line is shorted at the far end?

A very low impedance
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Wednesday, April 15, 2015

YLRL nets - everyday



Alaska Pacific Preparedness Net

14.292
1630 UTC (0830 Alaska Standard time)
Monday-Friday


Tangle Net

14.297
1800 UTC
Thursday
Pat K7DUC - net control
Sue KA6SOC - assistant net control

Because of interference, we will start at 14.297 but will then move to 14.297.50. This sure helps with the QRM.


Thursday Night YL Net

0100 UTC (Summer) or 0200 UTC (Winter)
20M (14.288.0+/- & 40M (7.198+/-)
Starts alternate weekly between the 2 bands
Net starts on the hour on one band and switches on the 1/2 to the other
Anne WB1ARU - Net Control
All YLs are encouraged to call and contact any YL they can hear on either band.


Thursday Night 2M/EchoLink YL Net

Please invite all YLs you know to join us! YL Net begins at 8:00 PM EDT Thursday which currently equates to 0000 UTC Friday. You can join via RF on 145.47 (-) PL 100.0Hz or
ECHOLink Node 560686 (NF4GA-R).

TIME CHANGE NOTE! PLEASE READ- United States has moved to Daylight Saving Time. Therefore, the YL Net starts at 0000 UTC Friday Each Week Until November 2015! This keeps the net to 8 pm Eastern (Daylight)



if YOU know of any more YL nets please send details to ka1uln@mail.com

thanks a bunch


YL challenge for certificates and QSO's

Yl's Amateur Radio Operators have been challenged to EARN YLRL certificates.

1. information about YLRL certificates are here: http://ylrl.org/index.php/ylrl-certificates

2. who can get the most YL contact in the Month of May 2015?



check out YLRL facebook or YLRL.org for more information

good luck

33
KA1ULN




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