Radio Propogation, Reception and Communication

Question 1

What is the speed of electromagnetic waves?

Answer 1

3 x 10^8 metres per second

Question 2

Do EM waves require a medium to transmit through?

Answer 2

No

Question 3

What is a wave cycle?

Answer 3

A single complete execution of a repeated phenomenon

Question 4

What is the wavelength of an EM wave?

Answer 4

Distance between two points of the same phase in consecutive cycles of a wave.

Question 5

What is the frequency of an EM wave?

Answer 5

• The number of cycles of an electromagnetic wave occurring in 1 second.
• Measured in Hz

Question 6

What is the relationship between wavelength and frequency?

Answer 6

V = f x wavelength

Question 7

What is the frequency spectrum?

Answer 7

The spread of possible electromagnetic frequencies.

Question 8

What are the three main frequencies used in aviation?

Answer 8

1) High frequency (HF)
2) Very High Frequency (VHF)
3) Ultra High Frequency (UHF)

Question 9

What are some positives and negatives of HF ?

Answer 9

• Excellent long distance qualities
• Doesn’t rely on like if aight
• Suffers from low equality transmission due to interference
• Is not used at airfields

Question 10

What frequencies are HF typically? What are HF frequencies used for?

Answer 10

• 3 - 300 MHz

- Used for HF comms

Question 11

What are some positives and negatives of VHF frequencies?

Answer 11

• High quality
• Low loss
• Line of sight communications between A/C and ground stations
• Short range
• Ideal for local airfield communications

Question 12

What is the frequency band for VHF ?

What are they used for?

Answer 12

• 30 - 300 MHz
• VHF comms
• Direction Finding
• VHF Omni Ranging (VOR)
• Marker Beacons
• ILS localiser

Question 13

What are some positives of Ultra High Frequency (UHF) waves?

Answer 13

• Clear signals with high fidelity which are easy to read
• Require line of sight
• Used for short distance communications
• Military used UHF 225 - 400 MHz

Question 14

What is the frequency band for UHF? What is it used for?

Answer 14

300 - 3000 MHz

• Distance Measuring Equipment (DME)
• GPS
• ILS Glideslope

Question 15

What is the design of a typically radio transmitter?

Answer 15

• Radio Frequency (RF) oscillator which generates the carrier wave
• The microphone which converts sound pressure waves into low level electrical energy
• The processed speech is amplified by an audio amplifier and transferred to the modulator which varies the carrier wave frequency
• The RF amplifier increases the power in the RF amplifier and radiates into space via the antenna.

Question 16

What is the purpose of a radio receiver?

Answer 16

Works in reverse to a transmitter

Question 17

What are the three types of radio wave propogation of interest to aviators?

Answer 17

1) Ground waves
2) Sky waves
3) Direct Waves

Question 18

What are ground waves?

Answer 18

• Frequencies between 30 kHz and 3,000 kHz
• Signals tend to follow the curvature of the earth
• Affected by the nature of the ground , salt water is best, sand is worse

Question 19

What are sky waves (Skip propogation)?

Answer 19

• Frequencies between 3 MHz and 30 MHz
• Radio waves are reflected or refracted back toward Earth from the ionosphere.
• The signal skips and creates a dead zone where a radio transmission will not be heard.

Question 20

What are direct waves?

Answer 20

Radio waves that are considered to travel in a straight line. (Line of sight).

Question 21

When may radio waves be refracted and change direction?

Answer 21

Boundary between coast and sea.

Question 22

What band of communication operates almost exclusively with sky waves?

Answer 22

HF band

Question 23

What is the critical angle when referencing sky waves?

Answer 23

The angle at which the first sky wave is returned to earth.

Question 24

What is the skip zone known as?

Answer 24

The distance between a transmitting station and the point at which the first reflected sky wave returns to earth.

Question 25

What is the dead zone?

Answer 25

Zone where neither sky wave or ground wave signals are present.

Question 26

What is the equation to determine line of sight range for VHF/UHF range?

Answer 26

D = 1.25 x sqrt(H1) + 1.25 x sqrt( H2)

Question 27

What is the purpose of an antenna?

Answer 27

Device used to radiate or receive EMR wave energy of a specific frequency.

Question 28

What is the impedance of the antenna?

Answer 28

• The resistance to an electrical signal within an antenna.

- impedance marching is where the impedance of the antenna matches the impedance of the transmitter or receiver.

Question 29

What is the radiation pattern gain?

Answer 29

The major direction in which EMR waves are either transmitted or received.

Question 30

What is the polarisation?

Answer 30

• The direction in which the electrical field oscillates

- Can be Vertical, horizontal or circular

Question 31

What are some factors that determine where the antennas are placed on an aircraft?

Answer 31

• Obstruction to signal réception
• Noise
• Aerodynamics effect
• Signal polarity
• Aircraft composition
• what antenna is used

Question 32

Where is ILS antenna ideally placed?

Answer 32

On the front of the aircraft.

Question 33

What are the different types of antenna?

Answer 33

• Half wave dipole
• Monopole
• Loop antenna
• Patch or plate antenna