Avionic systems integration

Question 1

What does TDM (Time division multiplexing) enable

Answer 1

TDM enables the information from many signal channels to be transmitted through a single communication system

Question 2

How much data can be transmitted through data highway

Answer 2

1 bit of information at a time

Question 3

Why is a coupler unit used to connect sub-systems to the data highway

Answer 3

So that if one sub-system short circuits, all other systems will still function

Question 4

Describe the MIL STD 1553 bus system

Answer 4

• developed in US military in 1970s
• adopted by NATO and given codification STANAG 3838

Data highway

• Bus controller
• remote terminal sub-system
• sub-system with RT capability

Bus if formed of a single twisted cable pair with a layer of shielding, with a maximum length of 100m

Data transmitted at 1 Mbits/s (slow)

Question 5

Describe Manchester bi-phase

Answer 5

a change is made every bit time, even if same output. This is so it is easier to see faults in the system

Question 6

List 3 types of words transferred

Answer 6

• command words
• data words
• status words

Question 7

Describe command words

Answer 7

For a 5-bit terminal address, 2^5 -1 terminals can be connected to the bus.
(this is because 11111 is a broadcast address to all)

• T/R bit = 0, the terminal is to receive
• T/R bit = 1, the terminal is to transmit
• the sub-address/mode field is used to route data to and from a location in the RT (remote terminal)

Question 8

Describe data words

Answer 8

16 bit data with 1 parity bit

Question 9

Describe status word

Answer 9

• the status word is the first word by an RT to a BC command
• it provides a summary of the status/health of the RT
• The RT address field confirms the correct RT is responding

Question 10

What is the response time of RT, when all data is recieved

Answer 10

14 microseconds

and inter-message gap is (2-5microseconds)

Question 11

Describe STANAG 3910 (Europe)

Answer 11

• uses fibre optics
• bus controller
• sub systems in and out
• higher speed data
• 31 subsystems max

Question 12

Describe Linear Token Passing Bus (USA)

Answer 12

• no specific bus controller, protocol is in each subsystem
• fibre optic star coupler
• 128 sub systems max

Question 13

What is electromagnetic interference

Answer 13

When voltages or currents are present and affect the performance of the device

Question 14

What is electromagnetic compatibility

Answer 14

The desired situation when a device or a system operates as intended within itself and its environments

Question 15

An EMI problem can be designated as:

Answer 15

• intrasystem: problem comes from the system itself

- intersystem: problem comes from outside the system

Question 16

An EMI problem arises because of the combination of 3 factors, these are:

Answer 16

• Source
• Transmission path
• Response

Question 17

When does arc discharge occur

Answer 17

Arc discharge occurs when the electric field intensity between two conductors exceeds the breakdown strength of the dielectric separating them

Question 18

What is the breakdown strength

Answer 18

A property of the dielectric, which could be a gas, a liquid or a solid :)

(Air: 30kV/mm)

Question 19

What is the Schumann resonance

Answer 19

After lightning the interference spans across several Hz to 100MHz. But at 8 Hz its level is increased and this is the Schumann resonance

Question 20

List three types of cosmic noise

Answer 20

• Galactic noise
• Thermal noise
• Anomalous solar noise

Question 21

How is precipitation static caused

Answer 21

It is caused by aircraft in flight coming in contact with uncharged particles

• the positive element of the particle is reflected away from the aircraft and the negative particle adheres to the skin
• If aircraft does not have sufficient static dischargers, it may go into “CORONA”

Question 22

List problems associated with p-static

Answer 22

• erratic instrument readouts
• erroneous magnetic compass readings
• complete loss of VHF communications
• weak transmissions and poor receptivity of radios
• VHF navigation system inoperative most of the time
• loss of all avionics in clouds