BASIC THEORY.
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C. RADAR MAINTENANCE.
44. Function of Radar as a navigational aid.
Fundamental Principles of Radar.
(1) Measurement of range interval as time interval. Accuracy of measur ment, measurement of time by C.R. Tube. Pulse transmission, bearing by beam- ing the transmission, minimum range, range discrimination, bearing discrimination. affect of pulse length. Peak power and average power. Effect of "beam width" on (4) bearing discrimination, (8) field strength at the target.
Radar mupo equation.
(2) Serles L.R. Circuits, growth and decay of current, lime constant. Series CR circuits, exponential charge and discharge curves, Ume constant numerical examples. Coupling circuit, differentiating circuit, integrating circuit. Ourpet from "CR circuit with square wave input graphs.
(3) Cathode biassing. H.T. potentiometer biassing. Grid return to H.T. grid current timiting. Series and Parallel limiting using diodes. DC restorer. Squaring circuits. Peaking circuits, trigger circuits. Paraphase amplifiers. Interelectrode capacitance of triode valve. Input impedance of triode with E. load, with reactive load. Negative feedback, Cathode followers.
(4) Phase shifting circuits. Phase shift oscillator. Blocking oscillator, R.C. transitron oscillator. Multivibrator:
free running, triggered, electron coupled.
Symmetrical and Asymmetrical.
Synchronization of multivibrator. Waveforms, frequency and period of multi- vibrators and oscillators. Production of variable length square pulse from trigger pulse.
(5) Cathode ray tubes, construction and action. Screen types, Electrostatic focus and deflection, shift, deflection distortion. Electromagnetic focus afþd declaration, shift. Use us a P.P.L. Cathode ray oscilloscope and its use lo waveform monitoring.
(6) Time Base requirements. Voltage waveform required for E.S. defect- tion. Simple sawtooth generator, pentode charging circuit, hand valve, time base. müller time base.
Current waveform required for E.M. daffection, voltage waveform required trapezoidal generator, power amplifiers, time base requirements for P.P.I. display. Rotating radial trace." Rotating deflector coils and driving systems. Rotating field, selsyn system. Power supply circuits, EHT from voltage multiplier rectifier systems using metal rectifiers. Need for voltage regulated HLT. (to time base and other circdits) Voltage regulator circuits.
(7) Need for brightening pulse. Brightening pulse circuits. Ringing oscil tator, use as a dolay circuit, use in calibraton circuits. Variable range marker. simple range marker circuit.
(8) Radar receivers. Signal to morse ratio, bank with requirements, wide bank IF. amplifiers, video amplifiers, series and shunt compensation of video amplifiers.
Need for synchronization of operations, Block diagram of synchronizing systenta. Delay circuits. Transmission lines. D.C. applied to transmission line, infinite line, shorted Lias, open line. Characteristic impedance, propagation time. A.C applied to a transmission line, infinite line, open line, shorted line. Reflection at mismatch, standing waves, standing wave ratio. Resonant line sections. Quarter wave and half wave open and shorted stubs. Duplexing by transmission line section. Transmission line as a delay circuit.
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(9) Transmission of Power at U.H.F. losses on transmission lines at U.H.F. waveguides, propagation in a waveguide. Rectangular and circular guides. Simple modes. Impedance matching. Irises, screws, stubs. Choke joints. Rotating joints.
Screw couplings, contact shims Waveguide attenuator. Waveguide duplexing system. Typical waveguide system. TŘ and TB hom radiator.
(30) Cavity resonators. Simple half wave cavity resonator. Types of cavity resonators. Methods of tuning. Limitations of valve oscillators at U.HF.. transit time, stray reactances. Performance monitors. Reflex klystron, methods of tuning, modes of oscillation and power output limitations. Resonant cavity magnetron.
Modulators, thyratron and irigatron, need for square pulse to magnetron. Artificial lines, as a pulse forming network, as a delay network. Artificial line charging circuits.
Pulse transformer.
(11) Double and single mixer systems. Crystal diodes. Automatic frequency control, basic principles, discriminator circuits. Control circuits. Concept of operating error of AFX system.
(12) Aerial arrays, polar diagrams, parabolic reflector, beam width. Side lobes. Lobes due to ground reflections.
(13) Sea clutter and anti-clutter devices. Fake and multiple echoes, blind sectors. Raccas, chart comparison units.
Anomalous propagation, Ramarks and
Written Examination.
45. This will be a 24 hours paper with a choice of questions.
(1) Questions set on the subject matter of the syllabus will ask for basic principles of the various operations in a radar set.
2) Descriptive treatment of the action of circuils and components with
the aid of diagrams, simple circuits and waveforms.
) Graphical treatment of charge and discharge of C through R and of pulse shapes concerned with differentiating and integrating circuits.
(4) Quantitative treatment of RC and LR time constants and differentiating and integrating circuits.
(5) Quantitative treatment of range measurement, minimum range, range discrimination, bearing discrimination, peak power and average power.
(6) Application of basic theory to the set with which the candidate is familiar with the aid of block schematic diagrams and waveforms.
TECHNICAL/PRACTICAL.
46. (1) (a) Block diagram of the installation.
Power supply circuits, motor alternator, starter and voltage regulator circuits.
(b) Location of parts.
Starting procedure. Routine maintenance.
(2)(a) The display unit Power supplies.
Circuits associated with the display:-time base circuits.
Calibration and/or variable range marker circuits.
Brightening pulse circuits.
Receiver, main IF. and video amplifiers.
Swept gain.
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