Radio principles

Question 1

Speed of sound sea level, 20,000 ft and 40,000 ft

Answer 1

Sea level = 660 kts
20,000 = 610 kts
40,000 = 570 kts

Question 2

Human ear frequencies

Answer 2

20-20,000hz

Question 3

Radio waves

Answer 3

Variation in strength of electric and magnetic fields.
Does not require medium.
Travel greater distance than sound.
Travel at speed of light (300,000km per second).H

Question 4

HF band

Answer 4

High frequency
3 MHZ to 30 MHZ
Commonly used for long distance communications

Question 5

VHF band

Answer 5

30 MHZ to 300 MHZ.
Preffered means of communication in aviation

Question 6

Why is VHF preffered

Answer 6

Large number of frequencies.
VHF frequencies less prone to interference

Question 7

Why VHF line of site

Answer 7

Can not bend around obstacles

Question 8

Why can HF frequencies bend

Answer 8

The variations in density of free electrons in the ionosphere cause HF radio waves to refract (bend), allowing the upper atmosphere to be used as a reflector for communications between distant locations on the ground.

Question 9

AM modulation

Answer 9

Amplitude modulation
Superimposing of intelligence on the carrier wave by varying the amplitude of the waves while the frequency remains constant. e.g. cardiograph

Question 10

FM modulation

Answer 10

Frequency modulation.
Superimposing intelligence upon the carrier wave by varying the frequency of the waves while amplitude remains constant.
Clearer signals and greater availability of channels within given frequency range than am

Question 11

Two types of microphones

Answer 11

Dynamic and electret
Electret is smallest and lightest, act on voice, ignore environmental sounds,

Question 12

Radio on procedure

Answer 12

Check avionics power switch on.
Check microphone and associated leads are plugged correctly.
Switch radio on.
Select desired frequency.
if audio panel fitted, select appropriate radio switch to speaker/phones.
Adjust volume and squelch to desired level.

Question 13

Radio not working procedure

Answer 13

Check master switch/avionics switch.
Check radio on/off switch, and NAV/COM set COM side is on.
Correct audio panel settings.
Check circuit breakers/fuses.
Check all connections (microphone/headphone plugs, correct socket).
Check correct frequency (COM not NAV).
Check volume and squelch (not fully anticlockwise)

Question 14

Transponder principle of opperation

Answer 14

Signal sent from sound based radar unit. Received by transponder. Transponder sends back coded signal to radar. Bearing and distance from ground radar (or ACAS) can be determined

Question 15

What mode information is transponder 4 figure code

Answer 15

Mode A - transmitted back to ground radar (or ACAS) upon each interrogation from originating unit

Question 16

Mode C information

Answer 16

Transmitter transmitting altitude with location.

Question 17

Transponder OFF mode

Answer 17

Transponder is off

Question 18

Transponder SBY

Answer 18

Transponder is on but will not reply to radar interrogation. Commonly used prior to take off and after landing.

Question 19

Transponder ON

Answer 19

Transponder on, reply to interrogation, will send mode A only (position and 4 digit code).

Question 20

Transponder ALT

Answer 20

Transponder on, reply to interrogation, Mode A (position and 4 digit code) and mode C (altitude) info sent. Function normally used when airborne.

Question 21

Transponder TEST

Answer 21

transponder test function.

Question 22

Common squawk codes

Answer 22

Fixed wing VFR is 1200
Rotor VFR is 1500
VFR circuit at controlled aerodrome is 2200
Unlawful interference 7500
Communications failure 7600
Emergency 7700

Question 23

HF radio uses

Answer 23

In areas where VHF reception is poor.
Aircraft leaving NZ for overseas as VHF coverage not available beyond certain distance.

Question 24

HF signal disadvantages

Answer 24

Static interference (not as clear as VHF).
Signal fading

Question 25

Antenna length rule

Answer 25

Antenna should be as long as half or quarter wave length.