Basic Theory

Question 1

State how electromagnetic waves are produced:

Answer 1

As electric current flows through a conductor it produces a magnetic field around it. In the case of a direct current it will produce a stationary magnetic field. However, an alternating current which comprises rapidly increasing and decreasing voltage will produce a magnetic field which also increases and decreases. As it does so, some of this pulsating energy becomes detached and is radiated outwards at the speed of light in the form of an electro-magnetic wave. Any receiving antenna which intercepts this EM wave will also receive the original alternating current.

Question 2

The definition of a cycle -

Answer 2

one complete series of values, from zero to maximum positive and back to zero, from zero to maximum negative and back to zero.

Question 3

The definition of amplitude -

Answer 3

The maximum displacement from the mean

Question 4

The definition of “frequency” -

Expressed as -

Answer 4

The number of cycles per second

hertz

Question 5

The definition of wavelength -

Answer 5

The distance travelled by the radio wave during the transmission of one complete cycle

Question 6

Wavelength =

Answer 6

speed of light / frequency in hertz

Question 7

Frequency =

Answer 7

Speed of light / wavelength in metres

Question 8

In which frequency band do NDBs operate?

Answer 8

LF and MF

Question 9

In which frequency band do VORs operate?

Answer 9

VHF

Question 10

In which frequency band do the ILS LOC operate?

Answer 10

VHF

Question 11

In which frequency band do DMEs operate?

Answer 11

UHF

Question 12

In which frequency band do the ILS GS operate?

Answer 12

UHF

Question 13

In which frequency band do Weather radar and doppler radar operate?

Answer 13

SHF

Question 14

The 3 types of radio waves(in terms of propagation):

Answer 14

1. Ground waves - bend and follow the curvature of the earth(diffraction)
2. Direct waves - follow a straight line of sight path
3. Sky waves - which are bent and returned to Earth by the ionosphere(refraction)

Question 15

Define attenuation:

Answer 15

Attenuation means a gradual loss of energy or signal strength. As the energy is spread over an ever increasing area the effective range is limited due to natural attenuation.

The ground over which the radio wave travels will absorb energy from the signal, as will the atmosphere through which it travels

Question 16

Which will have greater attenuation and diffraction(diffraction will lead to more greater range, since the waves will bend and follow the surface of the Earth), the lower frequencies or higher frequencies?

Answer 16

Lower frequency

Question 17

Which will have less attenuation and diffraction(diffraction will lead to greater range, since the waves will bend and follow the surface of the Earth), the lower frequencies or higher frequencies?

Answer 17

Higher frequencies

Question 18

The frequency bands which are direct waves and effectively line of sight?

Answer 18

VHF, UHF, SHF and EHF

Question 19

The range formula for direct waves:

Range in nm =

Answer 19

(1.25 x √transmitter height AMSL) + (1.25 x √receiver height AMSL )

Question 20

The type of wave propagation which is refracted(bent) and returned by the ionosphere -

Answer 20

sky waves

Question 21

The frequency bands which can propagate via sky waves?

Answer 21

HF and below(they posses diffraction)