A&P Flashcards
Properties of an antenna
Input impedence Polarisation Radiation pattern Gain Reletive efficiency
What are the frequency bands?
HF 3-30mhz
VHF 30-300mhz
UHF 300MHz-3ghz
SHF 3-30ghz
Types of wave
Sky wave (hf comms)
Surface wave
Space wave direct wave/ground reflected
Surface wave
Polarisation: ventricle and close to ground
Freq: lower the freq the greater the range
Ground: better conducter (water)
Space wave
Heightened the antenna greater direct wave, lower the antenna greater the ground reflective wave
Skywave
Higher the freq the longer the range
Lower the angle longer the range
Nvis
Near vertices incidence Skywave
Properties of an antenna
Input impedence Polarisation Radiation Gain Relative efficiency
Range for surface wave
100km
Range of sky wave
NVIS (short range) - 300km
Medium range - 300km - 1500km
Long range - 1500 - 3000km
Antenna height for Skywave vs range
Lower the antenna the shorter the range
Higher and broad side on will increase the range
Ionosphere
D
E
F1
F2
What happens to ionosphere at night
D+E disappear
F1+2 combine
Predictable ionosphere variations
Geographical closer to equator more ionosphere
Seasonal summer
Day/night
Sunspot cycle
Unpredictable variations
Solar flares
Magnetic storms
Sporadic E
Factors affecting all 3 types of propagation
Antenna
Noise
Power output of transmitter
Reliever
Characteristics of a radio wave
Frequency
Velocity
Wavelength
What is speed of light
300000000mps
What is frequency
Number of complete cycles in 1 second
What is wavelength
Distance wave has traveled In one second
Lambda
Relationship between freq and wavelength
Higher the freq the shorter the wavelength
Triangle
V
FXwavelength
Antenna material
R4 copper wire = 71.3 for quatre wavelength
Braid = 68.5
All other D10 = 68
Radio station
Power supply Intelligence input/output Transceiver RF transmitter/RF receiver Transmission line/coax Antenna
In a radio station what does a transceiver do
RF transmitter converts speech to RF
RF receiver converts RF to speech
What does an oscillator do
Turn power into current
What is resistance measured in
Ohms
Coax must be
Robust
Flexible
Easily matched to dipole
What makes impedence
Loss resistance
Radiation resistance
What is LR and RR
LR is physical resistance in antenna
RR is electrical resistance that Carrie across the antenna
Antenna matching
Right antenna for job
Dipole
Unipole
Unipole is 1/4 wavelength
It’s also earthed to make 1/2 wavelength
Dipole is 1/2 wavelength
Input impedence
Larger the antenna more resistance
Matched by the ATU (antenna tuning unit)
Polarisation
Vertically/polarised/directional
Radiation pattern
Eg broad side on Some antennas radiate more in one direction Position in correct direction Uni/monopole 360• Dipole need to be broad side on
Antenna gain
Directional
Measured in decibels
Antenna efficiency
Bad connection
ATU
Good earth
Relationship between frequency and range
Higher frequency the shorter the range because every wavelength that hits the ground reduces power
D layer
50km
Absorbs power during the day
Reduces noise
E layer
F1
F2
Refraction occurs
Noise created
