Podcast
Questions and Answers
For optimal transmission and reception, the transmitting and receiving antennas must both be of the same ______
For optimal transmission and reception, the transmitting and receiving antennas must both be of the same ______
polarization
During transmission over long distances, the ______ of waves changes (propagation effects)
During transmission over long distances, the ______ of waves changes (propagation effects)
polarization
Even if polarization is not matched, a signal is usually ______
Even if polarization is not matched, a signal is usually ______
received
An antenna can be a length of wire, a metal rod, or a piece of ______
An antenna can be a length of wire, a metal rod, or a piece of ______
An important criterion for radiation is that the length of the conductor be approximately one-half or one-quarter ______ of the ac signal
An important criterion for radiation is that the length of the conductor be approximately one-half or one-quarter ______ of the ac signal
Horizontally Polarized Electric field is ______ to the earth
Horizontally Polarized Electric field is ______ to the earth
Vertically Polarized Electric field is ______ to the earth
Vertically Polarized Electric field is ______ to the earth
Circular Polarization Electric and magnetic fields ______ as they leave the antenna
Circular Polarization Electric and magnetic fields ______ as they leave the antenna
Right-hand Circular Polarization (RHCP) rotates ______
Right-hand Circular Polarization (RHCP) rotates ______
Left-hand Circular Polarization (LHCP) rotates ______
Left-hand Circular Polarization (LHCP) rotates ______
Low-frequency Antennas: spacing may be 2 or ______ in.
Low-frequency Antennas: spacing may be 2 or ______ in.
Radiation pattern and gain of a folded dipole are the same as those of a standard dipole; offer greater ______
Radiation pattern and gain of a folded dipole are the same as those of a standard dipole; offer greater ______
When one-half wavelength is calculated, the velocity factor of twin-lead cable (0.8) must be ______
When one-half wavelength is calculated, the velocity factor of twin-lead cable (0.8) must be ______
Example: Find final length of a folded dipole antenna cut for 100 ______.
Example: Find final length of a folded dipole antenna cut for 100 ______.
Impedance matching antenna tuners are used when baluns and matching sections cannot do the job. They typically include a variable inductor, one or more variable capacitors, or a combination of these components. Inductor and capacitor values are adjusted until the ______ indicates that the impedances match.
Impedance matching antenna tuners are used when baluns and matching sections cannot do the job. They typically include a variable inductor, one or more variable capacitors, or a combination of these components. Inductor and capacitor values are adjusted until the ______ indicates that the impedances match.
An example of an Antenna Tuner is the Transmatch Circuit, which uses a coil and three capacitors to tune the antenna for optimal ______.
An example of an Antenna Tuner is the Transmatch Circuit, which uses a coil and three capacitors to tune the antenna for optimal ______.
In the Transmatch Circuit, the SWR meter is usually connected in series with the ______.
In the Transmatch Circuit, the SWR meter is usually connected in series with the ______.
In the context of Antennas and Waveguides, for optimal transmission and reception, the transmitting and receiving antennas must both be of the same ______.
In the context of Antennas and Waveguides, for optimal transmission and reception, the transmitting and receiving antennas must both be of the same ______.
For radiation to be effective, an important criterion is that the length of the conductor be approximately one-half or one-quarter of the AC ______.
For radiation to be effective, an important criterion is that the length of the conductor be approximately one-half or one-quarter of the AC ______.
A Marconi or Ground-Plane Vertical Antenna is one-quarter wavelength ____________ antenna
A Marconi or Ground-Plane Vertical Antenna is one-quarter wavelength ____________ antenna
An advantage of a Marconi or Ground-Plane Vertical Antenna is that it is one-half the length of a ________ antenna
An advantage of a Marconi or Ground-Plane Vertical Antenna is that it is one-half the length of a ________ antenna
The radiation pattern of a Marconi or Ground-Plane Vertical Antenna is still doughnut-shaped, but seen from above the ________
The radiation pattern of a Marconi or Ground-Plane Vertical Antenna is still doughnut-shaped, but seen from above the ________
An omnidirectional antenna has an equal amount of energy in the ________ direction
An omnidirectional antenna has an equal amount of energy in the ________ direction
The center conductor of a Marconi or Ground-Plane Vertical Antenna is connected to the vertical radiator, and the shield is connected to earth ________
The center conductor of a Marconi or Ground-Plane Vertical Antenna is connected to the vertical radiator, and the shield is connected to earth ________
An antenna with drooping radials can be adjusted using a 50Ω coaxial ________ line
An antenna with drooping radials can be adjusted using a 50Ω coaxial ________ line
A 5/8 λ Vertical Antenna is one-eighth wavelength longer than one-half wavelength and has about a 3-dB gain over a basic ________
A 5/8 λ Vertical Antenna is one-eighth wavelength longer than one-half wavelength and has about a 3-dB gain over a basic ________
Directivity in antennas refers to the ability to send or receive signals over a narrow horizontal ________ range
Directivity in antennas refers to the ability to send or receive signals over a narrow horizontal ________ range
A conventional half-wave dipole antenna is bidirectional, meaning it receives signals best in two directions, and unidirectional, meaning it sends or receives signals in one direction ________
A conventional half-wave dipole antenna is bidirectional, meaning it receives signals best in two directions, and unidirectional, meaning it sends or receives signals in one direction ________
Power gain is concentrated into a small beam, giving the effect as if the antenna had amplified the transmitted signal, this is known as ________ Gain
Power gain is concentrated into a small beam, giving the effect as if the antenna had amplified the transmitted signal, this is known as ________ Gain
Flashcards are hidden until you start studying
Study Notes
Antennas and Waveguides
- For optimal transmission and reception, the transmitting and receiving antennas must have the same polarization.
- During long-distance transmission, the polarization of waves changes due to propagation effects, but a signal can still be received even if the polarization is not matched.
The Basic Antenna
- An antenna can be a length of wire, a metal rod, or a piece of tubing.
- The length of the conductor is dependent on the frequency of operation, and an important criterion for radiation is that the length of the conductor be approximately one-half or one-quarter wavelength of the ac signal.
Common Antenna Types
- Marconi or Ground-Plane Vertical Antenna:
- One-quarter wavelength
- Omnidirectional antennas
- Radiation pattern is still doughnut-shaped, but seen from above the antenna
- Equal amount of energy in the horizontal direction
- One-half of the pattern is below the surface of the earth (vertical radiation pattern)
- Center conductor is connected to the vertical radiator, and the shield is connected to earth ground
- Earth acts as a type of electrical “mirror”
- Good electrical contact with the earth is necessary for effective operation
- A ground plane, radials, and counterpoise can be used to improve the antenna's effectiveness
- Radiation resistance is approximately one-half the impedance of the dipole (approximately 36.5Ω)
- May vary due to height above ground, length/diameter ratio, and presence of surrounding objects
- Loading Coil:
- Used to compensate for a vertical antenna that is less than one-quarter wavelength, which would decrease inductance and prevent resonance at the desired frequency
- Top Hat:
- Used to increase the effective capacitance of an antenna
- Adds conductors at the top of the antenna
- Arrangement is impractical and heavy
- 5/8 λ Vertical Antenna:
- One-eighth wavelength longer than one-half wavelength
- Gives about a 3-dB gain over a basic dipole
- Narrower vertical radiation pattern at a lower angle to the horizon
- Ideal for long-distance communication
Directivity
- Omnidirectional:
- Can send messages in any direction and receive them from any direction
- Directivity:
- Ability to send or receive signals over a narrow horizontal directional range
- Depends on physical orientation
- Eliminates interference from other signals
- Receiving antenna is pointed directly at the station
- Greater efficiency of power transmission
- Unidirectional:
- Sends or receives signals in one direction only
- Conventional Half-wave Dipole:
- Bidirectional – receives signals best in two directions
- Unidirectional – sends or receives signals in one direction only
Gain
- Power Gain:
- Concentrates power into a small beam, making it seem as if the antenna had amplified the transmitted signal
- 𝐏𝐭𝐫𝐚𝐧𝐬𝐦𝐢𝐭𝐭𝐞𝐝 𝐝𝐁 = 𝟏𝟎𝐥𝐨𝐠 𝐏𝐢𝐧
Relationship Between Directivity and Gain
- 𝐁= 𝟐𝟎𝟑 𝟏𝟎 𝐱
- B is the beam width of the antenna, in degrees
- x is the antenna power gain in decibels divided by 10 (x = dB/10)
- Assumes a symmetric major lobe
Polarization
- Horizontally Polarized:
- Electric field is parallel to the earth
- Vertically Polarized:
- Electric field is perpendicular to the earth
- Circular Polarization:
- Electric and magnetic fields rotate as they leave the antenna
- Depends on the direction of rotation
- Right-hand Circular Polarization (RHCP) - clockwise
- Left-hand Circular Polarization (LHCP) - counterclockwise
- Both transmitter and receiver must use either left- or right-hand polarization
- A vertical or horizontal antenna can receive circular polarized signals, but the signal strength is reduced
Impedance Matching
- Antenna Tuners:
- Used when baluns and matching sections cannot do the job
- A variable inductor, one or more variable capacitors, or a combination of these components
- Inductor and capacitor values are adjusted until the SWR indicates that the impedances match
- Example: Transmatch Circuit
- Uses a coil and three capacitors to tune the antenna for optimal SWR
- SWR meter is usually connected in series with the antenna
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
