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Flashcards in A&P Deck (40):
0

What are the frequency bands?

HF 3-30mhz
VHF 30-300mhz
UHF 300MHz-3ghz
SHF 3-30ghz

1

Properties of an antenna

Input impedence
Polarisation
Radiation pattern
Gain
Reletive efficiency

2

Types of wave

Sky wave (hf comms)
Surface wave
Space wave direct wave/ground reflected

3

Surface wave

Polarisation: ventricle and close to ground
Freq: lower the freq the greater the range
Ground: better conducter (water)

4

Space wave

Heightened the antenna greater direct wave, lower the antenna greater the ground reflective wave

5

Skywave

Higher the freq the longer the range
Lower the angle longer the range

6

Nvis

Near vertices incidence Skywave

7

Properties of an antenna

Input impedence
Polarisation
Radiation
Gain
Relative efficiency

8

Range for surface wave

100km

9

Range of sky wave

NVIS (short range) - 300km
Medium range - 300km - 1500km
Long range - 1500 - 3000km

10

Antenna height for Skywave vs range

Lower the antenna the shorter the range
Higher and broad side on will increase the range

11

Ionosphere

D
E
F1
F2

12

What happens to ionosphere at night

D+E disappear
F1+2 combine

13

Predictable ionosphere variations

Geographical closer to equator more ionosphere
Seasonal summer
Day/night
Sunspot cycle

14

Unpredictable variations

Solar flares
Magnetic storms
Sporadic E

15

Factors affecting all 3 types of propagation

Antenna
Noise
Power output of transmitter
Reliever

16

Characteristics of a radio wave

Frequency
Velocity
Wavelength

17

What is speed of light

300000000mps

18

What is frequency

Number of complete cycles in 1 second

19

What is wavelength

Distance wave has traveled In one second
(Lambda)

20

Relationship between freq and wavelength

Higher the freq the shorter the wavelength

21

Triangle

V
FXwavelength

22

Antenna material

R4 copper wire = 71.3 for quatre wavelength
Braid = 68.5
All other D10 = 68

23

Radio station

Power supply
Intelligence input/output
Transceiver RF transmitter/RF receiver
Transmission line/coax
Antenna

24

In a radio station what does a transceiver do

RF transmitter converts speech to RF
RF receiver converts RF to speech

25

What does an oscillator do

Turn power into current

26

What is resistance measured in

Ohms

27

Coax must be

Robust
Flexible
Easily matched to dipole

28

What makes impedence

Loss resistance
Radiation resistance

29

What is LR and RR

LR is physical resistance in antenna
RR is electrical resistance that Carrie across the antenna

30

Antenna matching

Right antenna for job

31

Dipole
Unipole

Unipole is 1/4 wavelength
It's also earthed to make 1/2 wavelength
Dipole is 1/2 wavelength

32

Input impedence

Larger the antenna more resistance
Matched by the ATU (antenna tuning unit)

33

Polarisation

Vertically/polarised/directional

34

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

35

Antenna gain

Directional
Measured in decibels

36

Antenna efficiency

Bad connection
ATU
Good earth

37

Relationship between frequency and range

Higher frequency the shorter the range because every wavelength that hits the ground reduces power

38

D layer

50km
Absorbs power during the day
Reduces noise

39

E layer
F1
F2

Refraction occurs
Noise created