This set of Avionics Multiple Choice Questions & Answers focuses on “Hyperbolic Radio Systems – 2”.

1. What is used to indicate that a baseline is not usable?
a) Blank
c) Pulse
d) Continuous wave

Explanation: The secondary stations blink to notify the user that a master secondary pair is unusable. Blink is repetitive on/off pattern of the first two pulses of the secondary signal.

2. Which mode of Loran-C requires a minimum of 3 transmitters with iterative computation to obtain a fix?
a) Hyperbolic mode
b) Rho-Rho-Rho
c) Rho-Rho-Theta
d) Rho-Theta-Zulu

Explanation: There are some Loran-C users who do not employ Loran-C in a hyperbolic mode but rather in the direct range rho-rho-rho mode. The rho-rho-rho process involves a minimum of three transmitter stations and the use of an iterative computation to obtain fix.

3. Which of the following is false about Direct ranging in Loran-C?
a) Uses Rho-Rho mode
b) Requires minimum 2 stations
c) Cost efficient
d) High stable user frequency standard

Explanation: Direct ranging Rho-Rho mode requires a minimum of two stations, a highly stable user frequency standard and precise knowledge of the time of transmission of the signal. The use of this mode is limited by the high cost of stable frequency standard.

4. Which of the following advantages does the differential Loran-C provide?
a) Stable user frequency
b) No seasonal errors
c) Cost efficient
d) Very high range of 500miles

Explanation: The corrections using differential Loran-C are generally valid for the co-relation distance of approximately 100 miles from the reference station. Real time co-relations remove both seasonal and diurnal errors can be broadcast.

5. Which of the following methods breaks the signal into finite segments to find the ASF?
a) Millington’s method
b) Bill’s method
c) Differential method
d) Table look up process

Explanation: In Millington’s method, the signal between the transmitter and the receiver is broken down into finite segments of different conductivity levels, based on conductivity maps. The incremental phase delay is then computed as a function of range and conductivity for each path segment summed and averaged to provide an estimate of ASF.

6. What is the number of systems used for redundancy in a transmitting station?
a) 2
b) 1
c) 5
d) 3

Explanation: Each transmitter station is physically divided into two groups of units to provide system redundancy. At the appropriate interfaces switching units are provided between them.

7. Which of the following derives all the signals needed by the transmitter from the timer?
a) PATCO
b) ECD
c) HCG
d) TOPCO

Explanation: Dual redundant pulse amplitude and timing controllers or PATCO accept timing signals from the timer and derive from this all the signals needed by the transmitter. Signals generated by the PATCO include start triggers, charging triggers, digital amplitude reference signals, amplitude compensation signals, and megatron reference trigger.

8. In Omega system, a given frequency is transmitted by only one station at any given time.
a) True
b) False

Explanation: In the Omega system, each station transmits continuous wave signals on four common frequencies and one station unique frequency. The signal frequencies are time shared among the stations so that a given frequency is transmitted by only one station at any given time.

9. HCGs are the power generators of the Loran-C transmitter stations.
a) True
b) False

Explanation: Each HCG or half-cycle generators contributes to the power contained in the Loran-C pulse. 32 HCGs comprises the standard set. The basic set can be expanded in multiples of eight HCGs.

10. What is the use of notch filters in Loran-C receivers?
a) Reduce interference from other frequencies
b) Reduce interference from other stations
c) Reduce interference from sky waves
d) Reduce atmospheric noise

Explanation: Loran-C signal reception can be impaired by interference from other signal broadcast on slightly different frequencies. To avoid degradation of S/N associated with these interfering sources, Loran -C sets are equipped with notch filters.

11. What type of transmission is used in Omega system?
a) Amplitude modulated wave
b) Continuous wave
c) Phase modulated wave
d) Frequency modulated wave

Explanation: At each Omega station, continuous wave signals on four common frequencies and one station unique frequency. The signal frequencies are time shared among the stations so that a given frequency is transmitted by only one station at any given time.

12. Which of the following type is not used in an Omega system?
a) Grounded tower
b) Insulated tower
c) Hanging tower
d) Valley span

Explanation: Since the Omega stations transmit in very low frequencies, the antennas are the largest physical structures in the stations. Three types of antennas are employed in the Omega system: grounded tower, insulated tower, and the valley span.

13. _____ acts as a coarse tuning device for the antenna?
a) Loop
b) Helix
c) Amplifiers
d) Filters

Explanation: The RF signal that is to be transmitted is transferred to the ‘Helix,’ a large helical coil that acts as a coarse tuning device for the antenna. The helix is equipped with separate taps for each signal frequency transmitted.

14. What type of transmitter is used in a Decca system?
a) Frequency synthesizer
b) Local oscillator
c) Crystal controlled
d) Digital

Explanation: A typical Decca chain consists of a master station and three slave stations. A station has a 2kW crystal controlled transmitter feeding a 300ft antenna.

15. What is the approximate range of Chayka system?
a) 200mi
b) 100mi
c) 300mi
d) 1000mi

Explanation: Chayka is a pulse phase radio navigation system similar to the Loran-C system. By using ground waves at low frequencies, the operating range is 1000mi and by using pulse techniques, sky wave contamination can be avoided.

Sanfoundry Global Education & Learning Series – Avionics.

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