01 Basic Radio Theory

Question 1

What is the speed of sound in:

• m/s
• nm/s

Answer 1

• 3 x 10^8 m/s

- 162,000 nm/s

Question 2

What is the definition of 1 Hz?

Answer 2

1 Hz = 1 cycle per sec

Question 3

What are the following in Hz?

• kHz
• MHz
• GHz

Answer 3

• 1 kHz = 1,000 Hz
• 1 MHz = 1,000,000 Hz
• 1 GHz = 1,000,000,000 Hz

Question 4

What is the equation for the Frequency of a wave?

Answer 4

Frequency = Speed of light (c) / Wave length (lander)

Question 5

What are the frequency bands and the associated frequency ranges?

Answer 5

• VLF: 3 - 30 kHz
• LF: 30 - 300 kHz
• MF: 300 - 3000 kHz
• HF: 3 - 30 MHz
• VHF: 30 - 300 MHz
• UHF: 300 - 3000 MHz
• SHF: 3 - 30 GHz
• EHF: 30 - 300 GHz

Question 6

What is the nemonic used to remember the frequency bands?

Answer 6

Very Low Minima Has Victor Using Safety Equipment

Question 7

What is the Doppler effect?

Answer 7

The apparent frequency shift which occurs when the transmitter and receiver are moving relative to each other.

Frequency appears to increase if they are moving towards each other and decreases if they are moving away from each other.

Question 8

What is the equation for the Doppler Shift?

Answer 8

Doppler Shift = Relative Velocity (m/s) / Transmitted Wave length (m)

Question 9

What are the four types of Modulation?

Answer 9

• Pulse Modulation: Length of a pulse is called the pulse width
• Amplitude Modulation: Info is encoded through changes in amplitude
• Frequency Modulation: info is encoded through changes in frequency
• Phase Modulation: Complex modulation technique

Question 10

What are the main factors which effect the propagation of a radio wave?

Answer 10

• Type of the Antenna
• Frequency
• Weather
• Ionosphere
• Solar activity
• Reflection
• Refraction
• Absorption
• Diffraction
• Interference

Question 11

What are the three category’s of radio wave?

Answer 11

• Ground / Surface Wave: Low Frequency
• Sky Wave
• Space Wave: High Frequency

Question 12

What is the equation for the maximum theoretical range of a transmission?

Answer 12

D = 1.23 x (Sqrt(Tx) + Sqrt(Rx))

D is distance (nm)
Tx is transmitter height (ft)
Rx is Receiver height (ft)

Question 13

When an antenna is fed with AC current, the electromagnetic field generated comprises of what elements?

Answer 13

• Electric field (E Field): Parallel with the antenna

- Magnetic Field (H Field): Perpendicular with the antenna

Question 14

For high frequency signals (VHF, UHF, SHF, EHF) what form of propagation is associated with them?

Answer 14

Space Waves (line of sight waves)

Question 15

When is SSB (Single Side Band) used?

Answer 15

• Used for HF communications

- Saves power whilst maintaining range

Question 16

What is the Skip Distance?

Answer 16

The distance from the transmitter to the first Sky Wave

Question 17

What is the definition of Phase?

Answer 17

The fraction of one wavelength expressed in degrees (000 to 360)

Question 18

Are VHF and HF communications frequency or amplitude modulated?

Answer 18

Amplitude modulated

Question 19

What do each of the characters represent in the three character radio transmission classification?

Answer 19

• 1st character: Type of modulation of the main carrier
• 2nd character: Nature of the signal(s) modulating the main carrier
• 3rd character: Type of information to be transmitted