Basic Radio Theory

Question 1

What is the two parts a electro-magnetic wave consist of?

Answer 1

1. An electrical component

2. A magnetic component

Question 2

Define a EM “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

Define wavelength?

Answer 3

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

Question 4

Define “Phase”

Answer 4

This term refers to the stage, or position, of an alternating current expressed in degrees from 0 to 360 during a cycle

Question 5

What are the five stages during a cycle?

Answer 5

0, 90, 180, 270, 360

Question 6

State the 3 types of radio wave classifications

Answer 6

1. Ground Wave - Bend and follow the curvature of the earth’s surface (Diffraction)
2. Direct wave - Follow a straight line of sigh path
3. Sky wave - Which are bend and returned to earth by the Ionosphere (refraction)

Question 7

Define attenuation

Answer 7

Attenuation means a gradual loss of energy or signal strength, the ground over which the radio wave travels will absorb energy from the signal, as will the atmosphere through which it travels.

Question 8

What is the ideal length of a transmitter or receiver?

Answer 8

The wavelength of the frequency, half-wavelength is also acceptable.

Question 9

Which frequency will have more static?

Answer 9

As frequency increases, static decreases. VLF will have severe static.

Question 10

Which frequency will require more power?

Answer 10

Low frequency require very large power output to give the required range.

Question 11

Which frequency will have improved ground wave, or diffraction ability?

Answer 11

The lower the frequency, the more a radio wave will bend across the earth’s surface, aka improved diffraction.

VHF, UHF, SHF and EHF are direct waves.

Question 12

What is duct propagation?

Answer 12

This phenomenon is the result of meteorological conditions during which VHF, and higher, signals can be received at greater than normal distances.

Ideal conditions include a temp inversions with high humidity caused by warm air dry air passing over a cool sea.

Question 13

What is sky waves?

Answer 13

Sky waves are radio signals which are reflected by the ionosphere.

Question 14

Factors affecting sky waves:

How does the angle at which the radio waves strikes the ionosphere affect reflection?

Answer 14

The angle at which the radio wave strikes the ionosphere will determine whether the wave will return to earth or not, a small angle will not reflect the wave back to earth, as it will directly pass through the ionosphere. As the angle is increased, the signal is bend more and more until it is reflected back to earth as the first returning sky wave. This is called the critical angle.

Question 15

Factors affecting sky waves:

How does penetration depth affect range?

Answer 15

The depth that signal penetrates into an ionospheric layer before being refracted is a factor affecting range. The deeper the penetration, the greater the range.

Question 16

Factors affecting sky waves:

Explain skip distance

Answer 16

Skip distance is the distance from the transmitter to the point on the earths surface where the first sky ave returns.

Question 17

When calculating wavelength, do we use cm or m?

Answer 17

Metre.

Question 18

Factors affecting sky waves:

Explain dead space

Answer 18

If a frequency produces both ground and sky waves, there may be an area where no reception is possible. The dead space is between the limit of ground wave reception and the first sky wave.

Question 19

Factors affecting sky waves:

Fading

Answer 19

Fading is a condition in which strength reduces as the range from the transmitter the transmitter increases. If two waves arrive out of phase, they will cancel each other.

Fading normally occurs when radio energy arrives at a receiver as both a ground wave and a sky wave, or two sky waves.

Question 20

What is multi-hop refraction?

Answer 20

This phenomenon occurs when a returning sky wave, if the signal is strong enough, is reflected back into the ionosphere by the earth’s surface where it is refracted and returned to the surface again. This process can continue several times as long as the signal is strong.

Question 21

Voice communications:

For VHF:

What is the frequency band, transmission type, power and range.

Answer 21

118Mhz to 136Mhz (720 channels, 25 khz apart)

A3E Amplitude modulated, vertically polarized.

20 watts for max range

Line of sight.

Question 22

Voice communications:

For HF:

What is the frequency band, transmission type, power and range.

Answer 22

2 Mhz to 22 Mhz

A3E (double sideband0
J3E ( SSB single sideband)
Amplitude modulated

100 watts

Question 23

Define MUF

Answer 23

The maximum usable frequency is the frequency at which radio waves start to penetrate the ionosphere and escape into space. MUF changes from hour to hour, and from day to day. It depends on the state of ionosphere, and can drop as low as 5 mhz.

Question 24

At what time is the ionosphere the most dense?

Answer 24

During the day, and least dense during the night.

Question 25

At what time is the ionosphere altitude low?

Answer 25

During the day, and high during the night.

Question 26

Complete the sentence:

___ frequencies require high electron density for _______

Answer 26

high frequencies require high electron density for refraction

Question 27

Complete the sentence:

___ frequencies require low electron density for _______

Answer 27

low frequencies require low electron density for refraction

Question 28

Does the critical angle increase or decrease with higher frequencies?

Answer 28

The critical angle increases with higher frequencies

Question 29

Does the critical angle increase or decrease with lower frequencies?

Answer 29

The critical angle decreases with lower frequencies

Question 30

What is SELCAL?

Answer 30

Selective calling system relieves the pilot from continuously listening on VHF or HF frequencies.

A ground station transmits a group of coded tone pulses on the frequency in use. A decoder on board activates a flashing light and which notifies the pilot that he is being called by the ground station.

Question 31

Surface attenuation is greatest with?

Answer 31

The higher the frequency the greater the surface attenuation

Question 32

What is the lowest frequency where freedom from static interference can be guaranteed?

Answer 32

Start of VHF 30MHz

Question 33

Can VHF and above receive or transmit sky waves?

Answer 33

No, VHF and above are direct waves. No ground or sky waves can be transmitted

Question 34

Which frequencies will penetrate deeper into the ionosphere during sky wave transmissions?

Answer 34

Higher frequencies will penetrate deeper in the ionosphere

Question 35

When a radio wave moves from one medium to another, does the frequency change?

Answer 35

No, but the wavelength will change

Question 36

The other name for direct waves?

Answer 36

Space waves

Question 37

What is meant by keying A1A modulation?

Answer 37

Interrupting the carrier wave to break it into dots and dashes

Question 38

The gain of an aerial is a measure of its ability to:

Answer 38

Compensate for attenuation