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Navy Electricity and Electronics Training Series (NEETS)
Module 12—Modulation Principles
Chapter 3:  Pages 3-31 through 3-35

Module 12—Modulation Principles
Pages i - ix, 1-1 to 1-10, 1-11 to 1-201-21 to 1-30, 1-31 to 1-40,
1-41 to 1-50, 1-51 to 1-60, 1-61 to 1-70, 1-71 to 1-75, 2-1 to 2-10,
2-11 to 2-20, 2-21 to 2-30, 2-31 to 2-40, 2-41 to 2-50, 2-51 to 2-60,
2-61 to 2-64, 3-1 to 3-10, 3-11 to 3-20, 3-21 to 3-30, 3-31 to 3-35,
AI-1 to AI-6, Index-1 to 2, Assignment 1 , 2

COMMON-EMITTER DETECTOR


The COMMON-BASE DETECTOR is an amplifying detector that is used in portable receivers.
 

COMMON-BASE DETECTOR


 
The SLOPE DETECTOR is the simplest form of frequency detector. It is essentially a tank circuit tuned slightly away from the desired fm carrier.
The FOSTER-SEELEY DISCRIMINATOR uses a double tuned RF transformer to convert frequency changes of the received fm signal into amplitude variations of the RF wave.
 
 

FOSTER-SEELEY DISCRIMINATOR


 
The RATIO DETECTOR uses a double-tuned transformer connected so that the instantaneous frequency variations of the fm input signal are converted into instantaneous amplitude variations.


3-31


 


RATIO DETECTOR

 


The GATED-BEAM DETECTOR uses a specially-designed tube to limit, detect, and amplify the received fm signal.
 

GATED-BEAM DETECTOR


 
PHASE DEMODULATION may be accomplished using a frequency discriminator or a quadrature detector.
 

PHASE DEMODULATION



3-32



 


PEAK DETECTION uses the amplitude, or duration, of a pulse to charge a holding capacitor and restore the modulating waveform.
 

PEAK DETECTION


 
A LOW-PASS FILTER is used to demodulate DM by averaging the pulse amplitude over the entire period between pulses.
PULSE CONVERSION is used to convert PPM, PDM, or PCM to PDM or PAM for demodulation.



ANSWERS TO QUESTIONS Q1. THROUGH Q40.
 
A-1. Re-creating original modulating frequencies (intelligence) from radio frequencies.
 
A-2. Circuit in which intelligence restoration is achieved.

A-3. A circuit that can detect the presence or absence of RF energy.

A-4. An antenna, tank circuit for tuning, rectifier for detection, filter to give constant output, and an indicator device.

A-5. Heterodyning.
A-6. By giving a different beat frequency for each signal.

A-7. Regenerative detector.

A-8. Oscillator, mixer, and detector.

A-9. (1) Sensitive to the type of modulation applied, (2) nonlinear, and (3) provide filtering.

A-10. The modulation envelope.

A-11. Rectifies the RF pulses in the received signal.


3-33




A-12. To filter the RF pulses and develop the modulating wave (intelligence) from the modulation envelope.

A-13. The current-diode detector is in parallel with the input and load.

A-14. When the input voltage variations are too small to give a usable output from a series detector.

A-15. Emitter-base junction.

A-16. R1.

A-17. By the collector current flow through R4.

A-18. Emitter-base junction.

A-19. A diode detector followed by a stage of audio amplification.

A-20. C1 and R1.

A-21. Slope detector.

A-22. Converting frequency variations of received fm signals to amplitude variations.

A-23. A double-tuned tank circuit.

A-24. Rectify the RF voltage from the discriminator.

A-25. Inductive.

A-26. Suppresses amplitude noise without limiter stages.

A-27. It helps to maintain a constant circuit voltage to prevent noise fluctuations from interfering with the output.

A-28. Limits, detects, and amplifies.
A-29. Both grids must be positively biased.

A-30. Extreme simplicity, few components, and ease of adjustment.

A-31. In the amount and rate of phase shift of the carrier wave.

A-32. Because of the incidental frequency shift that is caused while phase-shifting a carrier wave that is similar to fm modulation.

A-33. The quadrature grid signal is excited by a reference from the transmitter.

A-34. Detecting the presence of RF energy.

A-35. Pulse amplitude or pulse duration.

A-36. At least 10 times the interpulse period.

A-37. By making the time constant for charging the capacitor at least 10 times the maximum received pulse width.


3-34




A-38. By averaging the value of the pulses over the period of the pulse-repetition rate.
 
A-39. PPM, PFM, and PCM are converted to either PDM or PAM for demodulation.
 
A-40. It will discharge to one-half its value between pulses.























3-35



Introduction to Matter, Energy, and Direct Current, Introduction to Alternating Current and Transformers, Introduction to Circuit Protection, Control, and Measurement, Introduction to Electrical Conductors, Wiring Techniques, and Schematic Reading, Introduction to Generators and Motors, Introduction to Electronic Emission, Tubes, and Power Supplies, Introduction to Solid-State Devices and Power Supplies, Introduction to Amplifiers, Introduction to Wave-Generation and Wave-Shaping Circuits, Introduction to Wave Propagation, Transmission Lines, and Antennas, Microwave Principles, Modulation Principles, Introduction to Number Systems and Logic Circuits, Introduction to Microelectronics, Principles of Synchros, Servos, and Gyros, Introduction to Test Equipment, Radio-Frequency Communications Principles, Radar Principles, The Technician's Handbook, Master Glossary, Test Methods and Practices, Introduction to Digital Computers, Magnetic Recording, Introduction to Fiber Optics

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