E9D: Directional antennas: gain; satellite antennas; antenna beamwidth; losses; SWR bandwidth; antenna efficiency; shortened and mobile antennas; grounding
E9D01:
How does the gain of a parabolic dish antenna change when the operating frequency is doubled?
Gain increases 6 dB
Gain does not change
Gain is multiplied by 0.707
Gain increases 3 dB
E9D02:
What is one way to produce circular polarization when using linearly polarized antennas?
Arrange two Yagis perpendicular to each other with the driven elements at the same point on the boom and fed 90 degrees out of phase
Stack two Yagis, fed 90 degrees out of phase, to form an array with the respective elements in parallel planes
Stack two Yagis, fed in phase, to form an array with the respective elements in parallel planes
Arrange two Yagis collinear to each other, with the driven elements fed 180 degrees out of phase
E9D03:
How does the beamwidth of an antenna vary as the gain is increased?
It decreases
It increases geometrically
It increases arithmetically
It is essentially unaffected
E9D04:
Why is it desirable for a ground-mounted satellite communications antenna system to be able to move in both azimuth and elevation?
In order to track the satellite as it orbits the earth
So the antenna can be pointed away from interfering signals
So the antenna can be positioned to cancel the effects of Faraday rotation
To rotate antenna polarization to match that of the satellite
E9D05:
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
As low as possible on the vertical radiator
As close to the transmitter as possible
At a voltage node
E9D06:
Why should an HF mobile antenna loading coil have a high ratio of reactance to resistance?
To minimize losses
To swamp out harmonics
To maximize losses
To minimize the Q
E9D07:
What is a disadvantage of using a multiband trapped antenna?
It might radiate harmonics
It can only be used for single-band operation
It is too sharply directional at lower frequencies
It must be neutralized
E9D08:
What happens to the bandwidth of an antenna as it is shortened through the use of loading coils?
It is decreased
It is increased
No change occurs
It becomes flat
E9D09:
What is an advantage of using top loading in a shortened HF vertical antenna?
Improved radiation efficiency
Lower Q
Greater structural strength
Higher losses
E9D10:
What is the approximate feed-point impedance at the center of a folded dipole antenna?
300 ohms
72 ohms
50 ohms
450 ohms
E9D11:
Why is a loading coil often used with an HF mobile antenna?
To cancel capacitive reactance
To improve reception
To lower the losses
To lower the Q
E9D12:
What is an advantage of using a trapped antenna?
It may be used for multi-band operation
It has high directivity in the higher-frequency bands
It has high gain
It minimizes harmonic radiation
E9D13:
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
The resistance decreases and the capacitive reactance decreases
The resistance increases and the capacitive reactance decreases
The resistance increases and the capacitive reactance increases
E9D14:
Which of the following types of conductor would be best for minimizing losses in a station's RF ground system?
A thin, flat copper strap several inches wide
A resistive wire, such as a spark-plug wire
A cable with 6 or 7 18-gauge conductors in parallel
A single 12 or 10 gauge stainless steel wire
E9D15:
Which of these choices would provide the best RF ground for your station?
A connection to 3 or 4 interconnected ground rods driven into the Earth
A 50-ohm resistor connected to ground
A connection to a metal water pipe
A connection to 3 or 4 interconnected ground rods via a series RF choke
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