1. How is aliasing prevented?
a) Sampling at the same frequency of the original signal
b) Sampling at double the frequency of the original signal
c) Sampling at less than double the frequency of the original signal
d) Sampling at more than double the frequency of the original signal
Explanation: Aliasing occurs when the sampling rate is lower than the frequency of the original signal. The Nyquist theorem states that the sampling rate should be more than twice the frequency of the original signal to avoid aliasing
2. How is data staleness overcome?
a) Time synchronisation
b) Down conversion
c) Up conversion
d) Using multiple channels
Explanation: Data staleness problem it is necessary to have some form of time synchronisation of the computer iteration periods. This iteration period synchronisation is generally implemented through software.
3. Which of the following is not an advantage of using a digital data bus
a) Self test
b) Multiplexing
c) less weight
d) Not affected by electromagnetic interference
Explanation: Very large reductions in the weight of cabling are achieved by the use of multiplexed data transmission and data bus networks. High integrity data transmission can be achieved with very comprehensive self checking and data validation capabilities. However, they are heavily affected by electromagnetic interference.
4. What happens when the output of one channel is delayed by one iteration period before comparing with other channels in a quadruplex system?
a) Latency
b) Staleness
c) Aliasing
d) High noise
Explanation: Data staleness occurs when a channel is delayed by, say, one iteration, before comparison with others. To overcome this problem it is necessary to have some form of time synchronisation of the computer iteration periods.
5. Which of the following is true with respect to the passive optical sensor?
a) Not affected by EMI
b) Does not require an electrical supply
c) Output from the sensor is an optical signal
d) Processing this signal does not require any electrical device
Explanation: Passive optical sensors offers particular advantages as these sensors are not affected by EMI. Passive optical sensors are defined as sensors which do not require electrical supplies or any electronic processing at the sensor, the output of the sensor being an optical signal which is modulated by the quantity being measured. The processing of this optical signal is carried out by a separate electronic unit which is fully screened from EMI, the only connection between the sensor and the electronic unit being an optical fibre cable.
6. Which of the following affects the Fly-By-Wire system?
a) EMI
b) Lightning strikes
c) Flying in powerful Radio/Radar region
d) Bad weather
Explanation: One of the common modes of failure in the Fly-By-Wire system is EMI. Since the whole aircraft runs on electricity, Electromagnetic Interference heavily affects the FBW system. It is caused by lightning strikes and in regions of high power radio or radar.
7. What is EMP?
a) Electromagnetic pulse
b) Electromagnetic Power
c) Electromagnetic protection
d) Electrically Matched power line
Explanation: An EMP, abbreviated as Electromagnetic pulse is a sudden change in the magnitude of an electrical field(a pulse) with strengths of hundreds of volts per meter. It occurs in a very wide range of electromagnetic radiation spectrum and can damage any electrical equipment in its vicinity.
8. What is EMC?
a) Electromagnetic capture
b) Electromagnetic compatibility
c) Electromagnetic combat
d) Electromagnetic course
Explanation: EMC or Electromagnetic compatibility is the ability of the aircraft equipment to withstand high levels of EMI. This is a necessary condition as many cases have occurred of aircraft experiencing severe transients in the automatic flight control system placing the aircraft temporarily out of control whilst overflying high power radar/radio transmitters. This has been due to the susceptibility of the flight control system analogue electronics to EMI because of inadequate electro-magnetic screening.
9. What is nuclear hardness?
a) Ability to survive a nuclear explosion
b) Ability to survive in the vicinity of nuclear explosion
c) Ability to defend nuclear weapons
d) Ability to drop nuclear weapons with precision
Explanation: Vicinity to a nuclear explosion and consequent emission of gamma radiation and an EMP of very high electric field strength. Military avionic equipment is specially designed to survive up to a certain (classified) level of these effects. This attribute is referred to as ‘nuclear hardness’ and is achieved by the design of the circuits, use of nuclear hard components, circumvention techniques and very efficient electromagnetic screening.
10. Where is an EMC vault used?
a) Housing of FBW computer
b) Housing of all electronics
c) Screened enclosure around the connector
d) Shield for wires
Explanation: The wires from the cable connectors and the EM filters are housed within a screened enclosure around the connector known as an ‘EMC vault’ so that there is no aperture for EMI radiation to enter the box. The wires connecting different electrical equipment are the most affected by EMI.