B-006-10: Vertical antennas - types, dimensions, characteristics
B-006-10-01:
How do you calculate the length in metres (feet) of a quarter-wavelength vertical antenna?
Divide 71.5 (234) by the antenna's operating frequency (in MHz)
Divide 468 (1532) by the antenna's operating frequency (in MHz)
Divide 300 (982) by the antenna's operating frequency (in MHz)
Divide 150 (491) by the antenna's operating frequency (in MHz)
B-006-10-02:
If you made a quarter-wavelength vertical antenna for 21.125 MHz, how long would it be?
3.36 metres (11.0 ft)
3.6 metres (11.8 ft)
7.2 metres (23.6 ft)
6.76 metres (22.2 ft)
B-006-10-03:
If you made a half-wavelength vertical antenna for 223 MHz, how long would it be?
64 cm (25.2 in)
128 cm (50.4 in)
105 cm (41.3 in)
134.6 cm (53 in)
B-006-10-04:
Why is a 5/8-wavelength vertical antenna better than a 1/4-wavelength vertical antenna for VHF or UHF mobile operations?
A 5/8-wavelength antenna has more gain
A 5/8-wavelength antenna has less corona loss
A 5/8-wavelength antenna is easier to install on a car
A 5/8-wavelength antenna can handle more power
B-006-10-05:
If a magnetic-base whip antenna is placed on the roof of a car, in what direction does it send out radio energy?
It goes out equally well in all horizontal directions
Most of it is aimed high into the sky
Most of it goes equally in two opposite directions
Most of it goes in one direction
B-006-10-06:
What is an advantage of downward sloping radials on a ground plane antenna?
It brings the feed point impedance closer to 50 ohms
It increases the radiation angle
It brings the feed point impedance closer to 300 ohms
It lowers the radiation angle
B-006-10-07:
What happens to the feed point impedance of a ground-plane antenna when its radials are changed from horizontal to downward-sloping?
It increases
It decreases
It stays the same
It approaches zero
B-006-10-08:
Which of the following transmission lines will give the best match to the base of a quarter-wave ground-plane antenna?
50 ohms coaxial cable
300 ohms balanced feed line
75 ohms balanced feed line
300 ohms coaxial cable
B-006-10-09:
The main characteristic of a vertical antenna is that it will:
receive signals equally well from all compass points around it
be very sensitive to signals coming from horizontal antennas
require few insulators
be easy to feed with TV ribbon feeder
B-006-10-10:
Why is a loading coil often used with an HF mobile vertical antenna?
To tune out capacitive reactance
To lower the losses
To lower the Q
To improve reception
B-006-10-11:
What is the main reason why so many VHF base and mobile antennas are 5/8 of a wavelength?
The angle of radiation is low
The angle of radiation is high giving excellent local coverage
It is easy to match the antenna to the transmitter
It's a convenient length on VHF
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