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The correct answer is (c) Crystal CONTROLLED

To explain I WOULD say: 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.

The correct OPTION is (c) HANGING tower

The best I can explain: 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.

Correct answer is (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.

Correct ANSWER is (b) Continuous wave

For EXPLANATION I would say: 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.

Correct CHOICE is (a) Reduce INTERFERENCE from other frequencies

To explain I would say: 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.

The correct option is (a) True

For 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.

Right answer is (a) PATCO

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.

The correct option is (a) 2

For 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.

The correct choice is (a) Millington’s method

Best 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.

Correct choice is (b) No seasonal ERRORS

For EXPLANATION I would say: 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.

The correct choice is (b) Rho-Rho-Rho

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.

Correct choice is (c) Cost efficient

The explanation is: 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.

The correct ANSWER is (b) Blink

The explanation is: 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.

Correct answer is (a) Composite Omega

For explanation I would say: The composite Omega TECHNIQUE reduces the diurnal variation but does LITTLE to reduce the WIDE variation in phase behaviour EXHIBITED by paths of equal length over SUBSTANTIALLY electromagnetic/geophysical environments.

Right choice is (b) Acts as relays

The explanation: Each station has a signal MONITORING facility that is situated 20 to 50km away from the antenna. These stations perform FUNCTIONS such as MONITOR signal performance, provide the required data to phase synchronize the stations, and detecting solar terrestrial events that cause shifts in the PROPAGATED signal phase.

Right answer is (a) PGTR identification

The best explanation: PGTR or Pulse GROUP time reference identification is the process of ensuring that the RECEIVER is operating on the ground wave of the signal. The basic principle behind it is that ground WAVES travel FASTER than sky WAYS.

The CORRECT OPTION is (c) Diurnal

Explanation: The diurnal variations are short term propagation EFFECTS caused primarily by local weather changes and day/night transitions along the signal PATH. Variations in a refractive index of the ATMOSPHERE versus height from the ground contribute to the short term propagation errors.

The CORRECT answer is (a) Pulse trailing edge

To elaborate: The pulse trailing edge is defined as that portion of the Loran-C pulse following the peak of the pulse or 65μsec after the pulse is INITIATED. The pulse trailing edge is controlled in order to maintain SPECTRUM requirements.

The correct answer is (B) Blanking

Explanation: The LORAN signal FORMAT can be modified to accommodate a SINGLE transmitter station in two chains. This is ACCOMPLISHED by permitting transmission for one of the chains to take precedence over the other when the signal format calls for simultaneous transmission in both chains. This function is called blanking.

The correct option is (C) 100kHz

To elaborate: Each STATION transmits signals that have standard pulse leading edge characteristics. Each pulse CONSISTS of a 100kHz that rapidly increases in amplitude in a prescribed manner and then decays at a rate that depends on the PARTICULAR transmitter.

The CORRECT option is (a) 3

Best explanation: LORAN consists of transmitter stations in groups forming chains. At least three transmitter stations make up a chain. One station is DESIGNATED as the MASTER while the other is called secondaries.

The correct option is (d) Subjected to site errors

Easy explanation: The Loran stands for Long range navigation and USES GROUND waves with pulsed technique to avoid sky WAVE contamination. Being a HYPERBOLIC system, it is not subjected to the site errors of point source systems.

Right choice is (b) False

The best EXPLANATION: Loran is a hyperbolic navigational system that came into usage right before the outbreak of WORLD war II. The Loran-C uses ground WAVES at low frequencies, thereby securing an operating range of over 1000miles, independent of line of SIGHT.

Correct ANSWER is (a) Both measure the phase difference

The explanation: OMEGA and Decca measure the phase differences between the signals transmitted from PAIRS of stations while the Loran-C and Chayka measure the TIME difference between the SIGNAL from two or more transmitting stations.

Correct option is (d) 63Mhz above or below the received FREQUENCY

To elaborate: The Ground beacon in the DME RECEIVES the airborne pulses, and after a 50μs delay, retransmits them BACK to the aircraft on a frequency 63Mhz above or below the airborne TRANSMITTING frequency. Here the frequency received by the DME is the Airborne transmitting frequency.

Right ANSWER is (a) 12μsec

Easy explanation: The interrogation pulses are in pairs. Each PULSE is placed 12μsec apart with each pulse lasting 3.5μsec. The pulse pair repetition rate RANGES between 5 pulse pairs per sec to a maximum of 150 pulse pairs per sec.

Right option is (c) Alford loop

Explanation: Each radiator in the GROUND station transmitter is an Alford loop. The Alford loop GENERATES a horizontal polarized signal having the same FIELD PATTERN as a vertical DIPOLE.

Correct CHOICE is (c) 30rps

The explanation: The VOR sends out TWO signals. One is a HIGHLY directional signal that ROTATES at a frequency of 30 rps and an omnidirectional signal. The omnidirectional signal is pulsed every time the directional signal coincides with north.

The CORRECT answer is (d) 75MHz

The best I can explain: MARKER beacons were developed for better FIXES ALONG the airways in addition to directional information. They operate at 75MHz and RADIATE a narrow pattern upward from the ground.

The CORRECT answer is (d) No mountain and night effect

Easiest EXPLANATION: NDB uses ground waves which follow the curvature of earth. They are inexpensive and independent of accuracy issues but suffer from night effect and mountain effect. Mountain effect is the distortion of ground wave in terrain of NONUNIFORM CHARACTER.

Right choice is (c) Sense antenna

To explain: The HORIZONTAL pattern of the loop antenna is a figure of eight which has TWO null POSITIONS 180° apart. This ambiguity will cause the system to give the same indication whether it is pointing toward a station or AWAY from it. A sense antenna can be added when the signal ambiguity MUST be resolved.

Right OPTION is (d) GONIOMETER

Explanation: The goniometer has two sets of FIXED windings at right angles to each other, each set connected to one loop. It combines the OUTPUT from the loop antenna into miniature a MAGNETIC field in which a rotor can operate.

The correct option is (a) Horizontal polarization is ASSUMED

For explanation I would say: The loop antenna is a rectangular loop of wire whose inductance is RESONATED by a variable capacitor. The signal is assumed to be VERTICALLY polarized and the horizontal antenna PATTERN is a figure of eight. When the loop is 90° with respect to the TRANSMITTED signal the currents induced are of same amplitude and phase.

The correct choice is (c) Rotating loop

Best explanation: The rotating loop is driven by a motor and forming PART of a servo system that rotates the loop until a null is found and then stops. They are sometimes REFERRED to as the RADIO compass and are housed INSIDE plastic STRUCTURES that do not reflect radio waves.

The CORRECT ANSWER is (C) Very low error

The best explanation: Airborne direction FINDER or homing adapters take bearing from ground transmitters. These direction finders typically can AFFORD only the simplest of systems and must, therefore, tolerate large errors.

Correct option is (a) Ground based

To elaborate: Ground based direction FINDERS take bearings on AIRBORNE TRANSMITTERS and advice the aircraft of its bearing from the ground station. Such stations can afford the necessary complex equipment, but the operation is cumbersome and time CONSUMING, and requires airborne TRANSMITTER and communication link.

Correct option is (B) Pseudoranging

Easiest explanation: In this method, the user’s receiver and the reference STATION are assumed not to be synchronized in TIME. By measuring several such pseudoranges, the user’s three DIMENSIONAL position and its time offset can be DETERMINED.

Right choice is (a) True

The best EXPLANATION: A characteristic of GROUND WAVES is that their PROPAGATION velocity is not entirely constant. While the variation is quite small, it is sufficient to limit the ability to obtain fixes at EXTREME ranges as good as the instrumentation might otherwise permit.

The correct answer is (a) MULTIPATH effects

Best explanation: Serious distortion of signal modulation may occur due to DIFFERENT PATHS SIMULTANEOUSLY travelled by the signal between transmitter and receiver. These are called multipath effects.

Correct answer is (d) Day/night changes

Explanation: Propagation of ground waves depends on several additional factors. Some of which are conductivity and dielectric constant of earth. WEATHER changes like thunderstorms and LIGHTNING strikes also CREATE extra atmospheric noise and DEGRADE signal.