SUBELEMENT T9 – Radio waves, propagation, and antennas - 3 exam questions – 3 groups
T9A Antenna types – vertical, horizontal, concept of gain, common portable and mobile antennas, losses with short antennas, relationships between antenna length and frequency, dummy loads.
What is a beam antenna?
An antenna that concentrates signals in one direction
An antenna that concentrates signals in one direction
What is an antenna that consists of a single element mounted perpendicular to the Earth's surface?
A vertical antenna
A vertical antenna
What type of antenna is a simple dipole mounted so the elements are parallel to the Earth's surface?
A horizontal antenna
A horizontal antenna
What is a disadvantage of the "rubber duck" antenna supplied with most hand held radio transceivers?
It does not transmit or receive as effectively as a full sized antenna
It does not transmit or receive as effectively as a full sized antenna
How does the physical size of half-wave dipole antenna change with operating frequency?
It becomes shorter as the frequency increases
It becomes shorter as the frequency increases
What is the advantage of 5/8 wavelength over 1/4 wavelength vertical antennas?
Their radiation pattern concentrates energy at lower angles
Their radiation pattern concentrates energy at lower angles
What is the primary purpose of a dummy load?
It does not radiate interfering signals when making tests
It does not radiate interfering signals when making tests
What type of antennas are the quad, Yagi, and dish?
Directional or beam antennas
Directional or beam antennas
What is one type of antenna that offers good efficiency when operating mobile and can be easily installed or removed?
A magnet mount vertical antenna
A magnet mount vertical antenna
What is a good reason not to use a "rubber duck" antenna inside your car?
Signals can be 10 to 20 times weaker than when you are outside of the vehicle
Signals can be 10 to 20 times weaker than when you are outside of the vehicle
What is the approximate length, in inches, of a quarter-wavelength vertical antenna for 146 MHz?
19 inches
19 inches
What is the approximate length, in inches, of a 6-meter 1/2 wavelength wire dipole antenna?
112 inches
112 inches
T9B Propagation, fading, multipath distortion, reflections, radio horizon, terrain blocking, wavelength vs. penetration, antenna orientation.
Why are VHF/UHF signals not normally heard over long distances?
VHF and UHF signals are usually not reflected by the ionosphere
VHF and UHF signals are usually not reflected by the ionosphere
What might be happening when we hear a VHF signal from long distances?
A possible cause is sporadic E reflection from a layer in the ionosphere
A possible cause is sporadic E reflection from a layer in the ionosphere
What is the most likely cause of sudden bursts of tones or fragments of different conversations that interfere with VHF or UHF signals?
Strong signals are overloading the receiver and causing undesired signals to be heard
Strong signals are overloading the receiver and causing undesired signals to be heard
What is the radio horizon?
The point where radio signals between two points are blocked by the curvature of the Earth
The point where radio signals between two points are blocked by the curvature of the Earth
What should you do if a station reports that your signals were strong just a moment ago, but now they are weak or distorted?
Try moving a few feet, random reflections may be causing multi- path distortion.
Try moving a few feet, random reflections may be causing multi- path distortion.
Why do UHF signals often work better inside of buildings than VHF signals?
The shorter wavelength of UHF signals allows them to more easily penetrate urban areas and buildings
The shorter wavelength of UHF signals allows them to more easily penetrate urban areas and buildings
What is a good thing to remember when using your hand-held VHF or UHF radio to reach a distant repeater?
Keep the antenna as close to vertical as you can
Keep the antenna as close to vertical as you can
What can happen if the antennas at opposite ends of a VHF or UHF line of sight radio link are not using the same polarization?
Signals could be as much as 100 times weaker
Signals could be as much as 100 times weaker
What might be a way to reach a distant repeater if buildings or obstructions are blocking the direct line of sight path?
Try using a directional antenna to find a path that reflects signals to the repeater
Try using a directional antenna to find a path that reflects signals to the repeater
What term is commonly used to describe the rapid fluttering sound sometimes heard from mobile stations that are moving while transmitting?
Picket fencing
Picket fencing
Why do VHF and UHF Radio signals usually travel about a third farther than the visual line of sight distance between 2 stations?
The Earth seems less curved to radio waves than to light
The Earth seems less curved to radio waves than to light
T9C Feedlines types, losses vs. Frequency, SWR concepts, measuring SWR, matching and power transfer, weather protection, feedline failure modes.
What, in general terms, is standing wave ratio (SWR)?
A measure of how well a load is matched to a transmitter
A measure of how well a load is matched to a transmitter
What reading on a SWR meter indicates a perfect impedance match between the antenna and the feed line?
1 to 1
1 to 1
What might be indicated by erratic changes in SWR readings?
A loose connection in your antenna or feedline
A loose connection in your antenna or feedline
What is the SWR value where the protection circuits in most solid-state transmitters begin to reduce transmitter power?
2 to 1
2 to 1
What happens to the power lost in a feed line?
It is converted into heat by losses in the line
It is converted into heat by losses in the line
What instrument other than a SWR meter could you use to determine if your feedline and antenna are properly matched?
Directional wattmeter
Directional wattmeter
What is the most common reason for failure of coaxial cables?
Moisture contamination
Moisture contamination
Why is it important to have a low SWR in an antenna system that uses coaxial cable feedline?
To allow the efficient transfer of power and reduce losses
To allow the efficient transfer of power and reduce losses
What can happen to older coaxial cables that are exposed to weather and sunlight for several years?
Losses can increase dramatically
Losses can increase dramatically
Why is the outer sheath of most coaxial cables black in color?
Black provides protection against ultraviolet damage
Black provides protection against ultraviolet damage
What is the impedance of the most commonly used coaxial cable in typical amateur radio installations?
50 Ohms
50 Ohms
Why is coaxial cable used more often than any other feed line for amateur radio antenna systems?
It is easy to use and requires few special installation considerations
It is easy to use and requires few special installation considerations