Aircraft Antenna Considerations Flashcards
An antenna is the component of radio systems that is used to:
send or receive a radio signal
What does the antenna release in the form of an electromagnetic field to be sent to a distant receiver?
RF energy
What does the receiving antenna do?
absorbs the transmitted RF energy
Most aviation antennas are variations of three basic antennas:
Marconi (Macaroni)
Hertzian (Hershies)
Yagi-Uda (Yakisoba)
When used in line of sight applications, how do the antennas work best?
when the transmitting and receiving antennas are polarized the same
What is an Isotropic Radiator?
a one-dimensional point in space that transmits energy equally in all directions in a spheroid pattern with 100% efficiency
A Hertzian antenna is also known as:
a dipole and consists of two 1/4 wires placed end to end
Hertzian antennas radiate well where?
In directions perpendicular to the antenna, however they do not radiate at all off the wire tips
Because the radiated energy emitted from a hertzian antenna is concentrated broadside to the wire:
this type of antenna exhibits 2.1 db of gain when compared to an isotropic radiator
What systems are Hertzian antennas used in?
VHF Omnirange, localizer, and glideslope
How are Hertzian antennas used on aircraft polarized? (which direction)
Horizontally
Marconi antennas are commonly referred to as:
a vertical antenna
The vast majority of Marconi type antennas are polarized:
Vertically
The Marconi antenna radiates well where?
in all directions and considered to be an omnidirectional antenna. does not radiate well off the tips
What may be added when a marconi antenna is mounted on a tower?
A counterpoise
What does a counterpoise do?
it acts as ground and as the second 1/4 of the radiating element
Marconi antennas are used in aircraft with what systems?
VHF and HF communications, transponders, DME, GPS, and marker beacon systems
The Yagi-uda antenna is considered to be what type of antenna?
a unidirectional antenna.
This type focuses a majority of the radiation pattern in a single pattern
The yagi-uda antenna consists of a dipole element called:
the driven element
What are added to a yagi-uda antenna?
directors and reflectors
Where do Directors focus the energy?
toward the intended single direction
What do Reflectors do to the energy?
bounce the energy back in the intended direction
Directors and Reflectors are known as:
parasitic elements, since they have no direct electrical connection to the antenna
In comparison to the Hertzian antenna, the Yagi-uda antenna will exhibit how much gain?
8 dB due to the energy being focused in one direction
Antennas require what in order to receive and transmit the desired frequency?
they required a certain length. the length of the antenna will be equal to the frequency.
What does a loading coil do?
electronically lengthens an antenna while keeping it physically short
A loop antenna has the ability to what?
determine the direction a signal is coming from. This is known as a Directional Antenna
How does a loop antenna (or directional antenna) determine the direction of a frequency’s origin?
Signals are received at different strengths between coils inside of the antenna. The receiver then uses those differing strengths to determine the directions it’s coming from
Where can loop antennas on aircraft be found?
in the ADF and lightning detection systems
When installing antennas on aircrafts, they must be:
Structurally secure
Free from obstruction
Sealed from harsh environment
Free from interference from other antennas
What does STC stand for?
Supplemental Type Certificate
Some antennas, such as the Marconi and Hertzian, are:
Passive (non-powered)
What are Active (powered) antennas?
antennas that require the additional installment of a power supply and amplifiers or filters
What does TSO stand for?
Transportation Safety Office
To ensure an airworthy antenna installation, consult the technical specifications for:
Obstructions
Spacing
Noise reception
Vibration
Flutter
Static System Interference
Composite aircraft may need what?
a counterpoise
In some composite aircraft, a layer of:
conductive material may be a part of the outside structure
In the case of the aircraft having an outer layer of conductive material, the technician must:
ensure that the base of the antenna makes contact with the conductive surface
If the aircraft is not made of conductive material then:
an aluminum grounding plate may be used as a counterpoise
What does DER stand for?
Designated Engineering Representative
What might a technician have to calculate?
Dynamic load due to aerodynamic drag
Antennas should be mounted:
on a flat surface whenever possible
What is used if the curvature is too great for a gasket to seal the antenna?
A Mounting Saddle
How do you prevent moisture when mounting an antenna?
fill in any gaps with sealant
When troubleshooting a transmitter, it begins with:
a visual inspection
Reflected power will create what?
standing waves
What describes standing waves?
power dissipating within the transmission line
How do you measure standing waves?
calculate the voltage standing wave ratio (VSWR)
What does VSWR stand for?
Voltage Standing Wave Ratio
What is VSWR?
a comparison of the forward moving energy and reflected energy
(Standing Waves)
An excellent antenna has a VSWR of:
1.2:1 or less
Not only does a high VSWR create transmitter loss, but also creates:
a reception loss that increases as VSWR increases
What will a through line wattmeter not work for?
antennas connected to receivers
What is a duplexer?
a component that allows more than one receiver to share the same antenna
