Directional antennas: gain; satellite antennas; antenna beamwidth; losses; SWR bandwidth; antenna efficiency; shortened and mobile antennas; grounding
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E9D-2012: Directional antennas: gain; satellite antennas; antenna beamwidth; losses; SWR bandwidth; antenna efficiency; shortened and mobile antennas; grounding

E9D01-2012: How does the gain of an ideal parabolic dish antenna change when the operating frequency is doubled?

Gain increases by 6 dB

Gain does not change

Gain is multiplied by 0.707

Gain increases by 3 dB



E9D02-2012: How can linearly polarized Yagi antennas be used to produce circular polarization?

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



E9D03-2012: 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



E9D04-2012: 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



E9D05-2012: Where should a high-Q loading coil be placed to minimize losses in a shortened vertical antenna?

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



E9D06-2012: 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



E9D07-2012: What is a disadvantage of using a multiband trapped antenna?

It might radiate harmonics

It radiates the harmonics and fundamental equally well

It is too sharply directional at lower frequencies

It must be neutralized



E9D08-2012: 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



E9D09-2012: What is an advantage of using top loading in a shortened HF vertical antenna?

Improved radiation efficiency

Lower Q

Greater structural strength

Higher losses



E9D10-2012: What is the approximate feed point impedance at the center of a two-wire folded dipole antenna?

300 ohms

72 ohms

50 ohms

450 ohms



E9D11-2012: What is the function of a loading coil as used with an HF mobile antenna?

To cancel capacitive reactance

To increase the SWR bandwidth

To lower the losses

To lower the Q



E9D12-2012: What is one advantage of using a trapped antenna?

It may be used for multiband operation

It has high directivity in the higher-frequency bands

It has high gain

It minimizes harmonic radiation



E9D13-2012: What happens to feed point impedance at the base of a fixed-length HF mobile antenna as the frequency of operation is lowered?

The radiation resistance decreases and the capacitive reactance increases

The radiation resistance decreases and the capacitive reactance decreases

The radiation resistance increases and the capacitive reactance decreases

The radiation resistance increases and the capacitive reactance increases



E9D14-2012: Which of the following types of conductor would be best for minimizing losses in a station's RF ground system?

A wide flat copper strap

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



E9D15-2012: Which of the following would provide the best RF ground for your station?

An electrically-short connection to 3 or 4 interconnected ground rods driven into the Earth

A 50-ohm resistor connected to ground

An electrically-short connection to a metal water pipe

An electrically-short connection to 3 or 4 interconnected ground rods via a series RF choke





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E9C-2012: Wire and phased vertical antennas: beverage antennas; terminated and resonant rhombic antennas; elevation above real ground; ground effects as related to polarization; take-off angles
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