Sub Element G9: Antennas and Feed Lines Flashcards
Which of the following factors determine the characteristic impedance of a parallel conductor antenna feed line?
The distance between the centers of the conductors and the radius of the conductors
What are the typical characteristic impedances of coaxial cables used for antenna feed lines at amateur stations?
50 and 75 ohms
What is the typical characteristic impedance of “window line” parallel transmission line?
450 ohms
What might cause reflected power at the point where a feed line connects to an antenna?
A difference between feed-line impedance and antenna feed-point impedance
How does the attenuation of coaxial cable change as the frequency of the signal it is carrying increases?
Attenuation increases
In what units is RF feed line loss usually expressed?
Decibels per 100 feet
What must be done to prevent standing waves on an antenna feed line?
The antenna feed point impedance must be matched to the characteristic impedance of the feed line
If the SWR on an antenna feed line is 5 to 1, and a matching network at the transmitter end of the feed line is adjusted to 1 to 1 SWR, what is the resulting SWR on the feed line?
5 to 1
What standing wave ratio will result when connecting a 50 ohm feed line to a non- reactive load having 200 ohm impedance?
4:1
What standing wave ratio will result when connecting a 50 ohm feed line to a non- reactive load having 10 ohm impedance?
5:1
What standing wave ratio will result when connecting a 50 ohm feed line to a non- reactive load having 50 ohm impedance?
1:1
What is the interaction between high standing wave ratio (SWR) and transmission line loss?
If a transmission line is lossy, high SWR will increase the loss
What is the effect of transmission line loss on SWR measured at the input to the line?
The higher the transmission line loss, the more the SWR will read artificially low
What is one disadvantage of a directly fed random-wire HF antenna?
You may experience RF burns when touching metal objects in your station
Which of the following is a common way to adjust the feed-point impedance of a quarter wave ground-plane vertical antenna to be approximately 50 ohms?
Slope the radials downward
Which of the following best describes the radiation pattern of a quarter-wave, ground-plane vertical antenna?
Omnidirectional in azimuth
What is the radiation pattern of a dipole antenna in free space in a plane containing the conductor?
It is a figure-eight at right angles to the antenna
How does antenna height affect the horizontal (azimuthal) radiation pattern of a horizontal dipole HF antenna?
If the antenna is less than 1/2 wavelength high, the azimuthal pattern is almost omnidirectional
Where should the radial wires of a ground-mounted vertical antenna system be placed?
On the surface of the Earth or buried a few inches below the ground
How does the feed-point impedance of a 1/2 wave dipole antenna change as the antenna is lowered below 1/4 wave above ground?
It steadily decreases
How does the feed point impedance of a 1/2 wave dipole change as the feed point is moved from the center toward the ends?
It steadily increases