2016-E9D: Directional antennas: gain; Yagi Antennas; losses; SWR bandwidth; antenna efficiency; shortened and mobile antennas; RF Grounding
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
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 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
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
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
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
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
What is an advantage of using top loading in a shortened HF vertical antenna?
Improved radiation efficiency
Greater structural strength
What happens as the Q of an antenna increases?
SWR bandwidth decreases
SWR bandwidth increases
Gain is reduced
More common-mode current is present on the feed line
What is the function of a loading coil used as part of an HF mobile antenna?
To cancel capacitive reactance
To increase the SWR bandwidth
To lower the losses
To lower the Q
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
Which of the following types of conductors would be best for minimizing losses in a station's RF ground system?
A wide flat copper strap
A resistive wire, such as spark plug wire
A cable with six or seven 18 gauge conductors in parallel
A single 12 gauge or 10 gauge stainless steel wire
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
What usually occurs if a Yagi antenna is designed solely for maximum forward gain?
The front-to-back ratio decreases
The front-to-back ratio increases
The frequency response is widened over the whole frequency band
The SWR is reduced
● = Unseen
● = Weak
● = Review
● = Learned
● = Incorrect answer