Basic Radio Theory Flashcards
What is :
1-diffraction
2-critical angle
1-change in direction as a radio wave passes over Earth’s surface
2-angle at which radio wave leaves antenna
How are the electric and magnetic fields aligned in a vertically polarized antenna
Electric - vertical
Magnetic - horizontal
1-What is pulse modulation
2-what is pulse amplitude modulation (PAM)
3-what is pulse code modulation (PCM)
1-carrier transmitted in short pulses
2-amplitude of fixed series of pulses is modulated
3-each pulse amplitude is assigned either 1 or 0
How do FM transmitters differ from AM transmitters with regard to:
1-modulating power
2-reception
1-FM modulating power is lower
2-reception is static free
What is Depth of modulation
Extent to which carrier is modulated, expressed as percentage
What are sidebands
When rf carrier is AM, a single band of frequencies is produced above and below the carrier
Single Sideband Systems(SSB)
What is:
1-pilot carrier system
2-controlled carrier system
3-suppressed carrier system
1-a small carrier signal that is transmitted with the selected sideband, separated at receiver
2-carrier transmitted at full amplitude, between pauses in speech it is reduced
3-no carrier transmitted, all power contained in one sideband
What is a :
1-ground wave
2-direct wave
3-sky wave
1-a wave that follows Earth’s surface - VLF and HF
2-a wave that travels in straight lines - VHF and higher
3-waves refracted by ionosphere - HF
What are the 3 layers in the ionosphere
D layer
E / kenelley heaviside layer
F / Appleton layer
1-What properties does the ionosphere have during day
2-What properties does the ionosphere have during night
1-With large amount of UV radiation, abundance of free electrons
Said to be dense
All 3 layers present
2-less free electrons
Density decreases
D layer goes away, height of ionosphere increases
1-Does a radio wave have more/less refraction with a higher frequency
2-does the earth refract higher/lower frequencies during the day
1-Less
2- higher
What is :
1-skip distance
2-dead space
1-distance from transmitter to first touchdown point
2-distance between termination of ground wave and first touchdown point of sky wave
What is signal to noise ratio
A measure that compares level of desired signal to level of background noise
What frequency band is propagated as a space wave
VHF
What are 4 examples of directional antennas
Loop antenna
Parabolic antenna
Slotted planar antenna
Helical antenna
Which frequency band experiences fading during twilight hours
Medium Frequency
What is fading
Interference between the ground and sky wave
What frequency band is refracted in the ionosphere
HF
What is SSB commonly used in
HF communication
With regard to SSB transmission:
1-Is the beam width narrower or broader
2-how many frequencies is the power concentrated in
1-narrower
2-one or two instead of three
What type of transmission does HF/RT Selcal use
Modulating tones
