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T9AEdit

The T9A section covers antennas; vertical and horizontal, concept of gain, common portable and mobile antennas, relationships between antenna length and frequency.
Click "Expand" to reveal the questions.

T9A01

What is a beam antenna?
An antenna that concentrates signals in one direction

T9A02

Which of the following is true regarding vertical antennas?
The electric field is perpendicular to the Earth

T9A03

Which of the following describes a simple dipole mounted so the conductor is parallel to the Earth's surface?
A horizontally polarized antenna

T9A04

What is a disadvantage of the "rubber duck" antenna supplied with most handheld radio transceivers?
It does not transmit or receive as effectively as a full-sized antenna

T9A05

How would you change a dipole antenna to make it resonant on a higher frequency?
Shorten it

T9A06

What type of antennas are the quad, Yagi, and dish?
Directional antennas

T9A07

What is a good reason not to use a "rubber duck" antenna inside your car?
Signals can be significantly weaker than when it is outside of the vehicle

T9A08

What is the approximate length, in inches, of a quarter-wavelength vertical antenna for 146 MHz?
19

T9A09

What is the approximate length, in inches, of a 6 meter 1/2-wavelength wire dipole antenna?
112
Two approaches to solving this one. In the first, more formal, approach, you need to remember the formula
for calculating the HALFWAVE dipole length in feet is 468/frequency in MHz. Before we plug and chug, though, we have to calculate what that frequency is, so we have to go back to the old standby frequency in MHz = 300/wavelength in meters. So:
1. Calculate frequency. f = 300/6 = 50 MHz.
2. Calculate antenna length. length in feet = 468/50 = 9.36 feet.
3. Convert feet to inches. 9.36 feet * 12 inches/foot = about 112, which is the correct answer.
However, you really don't have to do all that much calculating since the possible answers are far apart from each other. Just remember that electricity doesn't move QUITE at the speed of light in a wire, so all we really have to do is take the halfwave length (6 meters/2)=3 meters, convert it to inches, and select the answer which isn't QUITE the number you calculated.
3 meters = 300 cm = (300/2.54) inches = 118 inches. Of the available choices, 112 fits the bill: 6 and 50 are way too short, and 236 is too long.

T9A10

In which direction is the radiation strongest from a half-wave dipole antenna in free space?
Broadside to the antenna

T9A11

What is meant by the gain of an antenna?
The increase in signal strength in a specified direction when compared to a
reference antenna

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