EQPS - Radio Principles

Question 1

What is Radio Attenuation? (3)

Answer 1

1. Audio information is limited in range
2. When VHF is used > Propagates over large distances
3. Each weakens over time & distance

Question 2

How do radio waves reduce in strength? (3)

Answer 2

Range or time from the point of transmission:

1. Ever-expanding wave front
2. medium through which the wave is passing resists the passage of energy passing through it

Question 3

Attenuation diagram

Answer 3

Strength diminishes with increasing distance but wavelength and frequency remain unchanged

Question 4

What are Wavebands? (1)

Answer 4

Radio waves are divided according to the frequency of the transmission into internationally recognised bands

Question 5

Wavebands diagram

Answer 5

Question 6

What is VLF characteristics and uses? (4)

Answer 6

1. Long range communications.
2. Requires immense aerials and high transmitter power.
3. Very prone to static interference.
4. Very long range navigation aids.

Question 7

What is LF & MF characteristics and uses? (6)

Answer 7

1. Reliable, long range communications.
2. Requires large aerials and high transmitter power.
3. Prone to static interference and night effect.
4. Very congested waveband.
5. NDB.
6. Some radio broadcasts.

Question 8

What is HF characteristics and uses? (6)

Answer 8

1. Long range communications by day and night limited by diurnal and seasonal variation of the ionosphere.
2. Requires smaller aerials and transmitter power.
3. Suffers from static interference and fading.
4. Optimum operating frequency varies diurnally.
5. Long distance wireless telegraphy.
6. RTF communications.

Question 9

What is VHF & UHF characteristics and uses? (7)

Answer 9

1. Line of sight communications.
2. Maximum range dependent upon aircraft height and aerial height.
3. Small aerial and transmission power.
4. Free from static interference and easy to suppress on aircraft.
5. Prone to ducting.
6. Wavebands become congested.
7. RTF, ILS, VOR, VDF, Surveillance Radar.

Question 10

What is SHF & EHF characteristics and uses? (7)

Answer 10

1. Short range communications.
2. Severe attenuation.
3. Precision, Surveillance and Airborne weather Radar.
4. Radio altimeter.

Question 11

Different Frequency Characteristics diagram

Answer 11

Question 12

Direct Wave diagram

Answer 12

• VHF and higher frequencies propagate on straight paths.
• Communication distances limited by the curvature of the Earth and aircraft height above sea level

Question 13

Ducted Wave diagram

Answer 13

• A marked temperature inversion plus a rapid decrease in humidity may form a duct within which VHF, UHF and SHF wavebands can unusually travel long distances
• The waves “bounce” between the surface and the top of the duct due to the ratio of wavelength to duct height

Question 14

Low Frequency Propagation Characteristics (Indirect wave)

Answer 14

• Similar to ducting, the low frequencies will bend around objects and be heard a great distance from the source.
• The low frequency means less attenuation