Ppm can be converted to pdm by using a flip-flop circuit. (Flip flops were discussed in NEETS, Module 9, Introduction to Wave-Generation and Wave-Shaping Circuits.) Figure 3-22 shows the waveforms for conversion of ppm to pdm. View (A) is the pulse-modulated pulse train and view (B) is a series of reset trigger pulses. The trigger pulses must be synchronized with the unmodulated position of the ppm pulses, but with a fixed time delay from these pulses. As the position-modulated pulse is applied to the flip-flop, the output is driven positive, as shown in view (C). After a period of time, the trigger pulse is again generated and drives the flip-flop output negative and the pulse ends. Because the ppm pulses are constantly varying in position with reference to the unmodulated pulses, the output of the flip- flop also varies in duration or width. This pdm signal can now be applied to one of the circuits that has already been discussed for demodulation.
Pulse-frequency modulation is a variation of ppm and may be converted by the same method.
3-26
Pulse-code modulation can easily be decoded, provided the pulse-code groups have been transmitted in reverse order; that is, if the pulse with the lowest value is transmitted first, the pulse with the highest value is transmitted last. A circuit that will provide a constant value of current without regard to its load is known as a current source. A current source is used to apply the pcm pulses to an RC circuit, such as that shown in figure 3-23, view (A). The current source must be capable of supplying a linear charge to C1 that will increase each time a pulse is applied if C1 is not allowed to discharge between pulses. In other words, if C1 charges to 16 volts during the period of one pulse, then each additional pulse increases the charge by 16 volts. Thus, the cumulative value increases by 16 volts for each received pulse. This does not provide a usable output unless a resistor is chosen that allows C1 to discharge to one-half its value between pulses. If only one pulse is received at T1, C1 charges to 16 volts and then begins to discharge. At T2 the charge has decayed to 8 volts and continues to decay unless another pulse is received. At T3 it has a 4-volt charge and at T4 it only has a 2-volt charge. At the sampling time, a 1-volt charge remains; this charge corresponds to the binary-weighted pulse train of 0001. Now we will apply a pcm signal which corresponds to the binary-coded equivalent of 7 volts (0111) in figure 3-23, view (A). View (B) is the pulse code that is received. Remember that the pulses are transmitted in reverse order. View (C) is the response curve of the circuit. At T1 the pulse corresponding to the least significant digit is applied and C1 charges to 16 volts. C1 discharges between pulses until it reaches 8 volts at T2. At T2 another pulse charges it to 24 volts. At T3, C1 has discharged through R1 to a value of 12 volts. The pulse at T3 increases the charge on C1 by 16 volts to a total charge of 28 volts. At T4, C1 has discharged to one-half its value and is at 14 volts. No pulse is present at T4 so C1 will not receive an additional charge. C1 continues to discharge until T5 when it has reached 7 volts and is sampled to provide a pam pulse which can be peak detected. This sampled output corresponds to the original sampling of the analog voltage in the modulation.
3-27
When the pcm demodulator recognizes the presence or absence of pulses in each position, it reproduces the correct standard amplitude represented by the pulse code group. For this reason, noise introduces no error if the largest peaks of noise are not mistaken for pulses. The pcm signal can be retransmitted as many times as desired without the introduction of additional noise effects so long as the signal-to-noise ratio is maintained at a level where noise pulses are not mistaken for a signal pulse. This is not the only method for demodulating pcm, but it is one of the simplest.
This completes your study of demodulation. You should remember that this module has been a basic introduction to the principles of modulation and demodulation. With the advent of solid-state electronics, integrated circuits have replaced discrete components. Although you cannot trace the signal flow through
3-28
these circuits, the end result of the electronic action within the integrated circuit is the same as it would be with discrete components.
Q-38. How does a low-pass filter detect pdm? Q-39. How is conversion used in pulse demodulation? Q-40. What is the discharge rate for the capacitor in a pcm converter?
Now that you have completed this chapter, a short review of what you have learned is in order. The following summary will refresh your memory of demodulation, its basic principles, and typical circuitry required to accomplish this task.
DEMODULATION, also called DETECTION, is the process of re-creating original modulating frequencies (intelligence) from radio frequencies.
The DEMODULATOR, or DETECTOR, is the circuit in which the original modulating frequencies are restored.
A CW DEMODULATOR is a circuit that is capable of detecting the presence of rf energy.
HETERODYNE DETECTION uses a locally generated frequency to beat with the cw carrier frequency to provide an audio output.
3-29
The REGENERATIVE DETECTOR produces its own oscillations, heterodynes them with an incoming signal, and detects them.
The SERIES- (VOLTAGE-) DIODE DETECTOR has a rectifier diode that is in series with the input voltage and the load impedance.
3-30
SHUNT- (CURRENT-) DIODE DETECTOR is characterized by a rectifier diode in parallel with the input and load impedance.
The COMMON-EMITTER DETECTOR is usually used in receivers to supply a detected and amplified output.
3-31
The COMMON-BASE DETECTOR is an amplifying detector that is used in portable receivers.
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.
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.
3-32
The GATED-BEAM DETECTOR uses a specially-designed tube to limit, detect, and amplify the received fm signal.
PHASE DEMODULATION may be accomplished using a frequency discriminator or a quadrature detector.
3-33
PEAK DETECTION uses the amplitude, or duration, of a pulse to charge a holding capacitor and restore the modulating waveform.
A LOW-PASS FILTER is used to demodulate pdm 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.
3-34
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.  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.
3-35
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.
AI-1
AMPLITUDE—Used to represent values of electrical current or voltage. The greater its height, the greater the value it represents.
ANGLE MODULATION—Modulation in which the angle of a sine-wave carrier is varied by a modulating wave.
AVERAGE POWER—The peak power value averaged over the pulse-repetition time.
BANDWIDTH—The section of the frequency spectrum that specific signals occupy.
BASE-INJECTION MODULATOR—Similar to control-grid modulator. Gain of a transistor is varied by changing the bias on its base.
BLOCKED-GRID KEYING—A method of keying in which the bias is varied to turn plate current on and off.
BUFFER—A voltage amplifier used between the oscillator and power amplifier.
CARBON MICROPHONE—Microphone in which sound waves vary the resistance of a pile of carbon granules. May be single-button or double-button.
CARRIER FREQUENCY—The assigned transmitter frequency. CARRIER—Radio-frequency sine wave.
CATHODE KEYING—A system in which the cathode circuit is interrupted so that neither grid current nor plate current can flow.
CATHODE MODULATOR—Voltage on the cathode is varied to produce the modulation envelope.
CHANNEL—Carrier frequency assignment usually with a fixed bandwidth.
COLLECTOR-INJECTION MODULATOR—Transistor equivalent of plate modulator. Modulating voltage is applied to collector circuit.
COMMON-BASE DETECTOR—An amplifying detector where detection occurs in emitter-base junction and amplification occurs at the output of the collector junction.
COMMON-EMITTER DETECTOR—Often used in receivers to supply detected and amplified output. The emitter-base junction acts as the detector.
COMPLEX WAVE—A wave composed of two or more parts.
CONTINUOUS-WAVE KEYING—The "on-off" keying of a carrier.
AI-2
CONTROL-GRID MODULATOR—Uses a variation of grid bias to vary the instantaneous plate voltage and current. The modulating signal is applied to the control grid.
CONVERSION—The process of changing ppm or pcm to pdm or pam to make them easier to demodulate.
CRYSTAL MICROPHONE—Uses the piezo-electric effect of crystalline materials to generate a voltage from sound waves.
CUSPS—Sharp phase reversals.
CW DEMODULATOR—A circuit that detects the presence of rf oscillations and converts them into a useful form.
CYCLE—360 degree rotation of a vector generating a sine wave.
DEMODULATION—The removal of intelligence from a transmission medium.
DEMODULATION or DETECTION—The process of re-creating original modulating- frequency intelligence from the rf carrier.
DEMODULATOR or DETECTOR—A circuit in which demodulation or restoration of the original intelligence is achieved.
DIODE DETECTOR—A simple type of crystal receiver.
DUTY CYCLE—The ratio of working time to total time for intermittently operated devices.
DYNAMIC MICROPHONE—A device in which sound waves move a coil of fine wire that is mounted on the back of a diaphragm and located in the magnetic field of a permanent magnet.
EMITTER-INJECTION MODULATOR—The transistor equivalent of the cathode modulator. The gain is varied by changing the voltage on the emitter.
FIDELITY—The ability to faithfully re-produce the input in the output.
FINAL POWER AMPLIFIER (fpa)—The final stage of amplification in a transmitter. FIXED SPARK GAP—A device used to discharge the pulse-forming network. A trigger pulse
ionizes the air between two contacts to initiate the discharge.
FOSTER-SEELEY DISCRIMINATOR—A circuit that uses a double-tuned rf transformer to convert frequency variations in the received fm signal to amplitude variations. Also known as a phase-shift discriminator.
FREQUENCY DEVIATION—The amount the frequency departs from the carrier frequency. FREQUENCY MODULATION (fm)—Angle modulation in which the modulating signal
causes the carrier frequency to vary. The amplitude of the modulating signal determines how far the frequency changes and the frequency of the modulating signal determines how fast the frequency changes.
FREQUENCY MULTIPLIERS—Special rf power amplifiers that multiply the input frequency.
AI-3
FREQUENCY—The rate at which the vector that generates a sine wave rotates. FREQUENCY-SHIFT KEYING (fsk)—Frequency modulation somewhat similar to
continuous-wave (cw) keying in AM transmitters. The carrier is shifted between two differing frequencies by opening and closing a key.
GATED-BEAM DETECTOR—An fm demodulator that uses a special gated-beam tube to limit, detect, and amplify the received fm signal. Also known as a quadrature detector.
signals. The incoming cw signal is mixed with locally generated oscillations to give an af output.
HETERODYNING—Mixing two frequencies across a nonlinear impedance.
HIGH-LEVEL MODULATION—Modulation produced in the plate circuit of the last radio stage of the system.
INSTANTANEOUS AMPLITUDE—The amplitude at any given point along a sine wave at a specific instant in time.
INTERMEDIATE POWER AMPLIFIER (ipa)—The amplifier between the oscillator and final power amplifier.
KEY CLICKS—Interference in the form of "clicks" or "thumps" caused by the sudden application or removal of power.
KEY-CLICK FILTERS—Filters used in keying systems to prevent key-click interference.
KEYING RELAYS—Relays used in high- power transmitters where the ordinary hand key cannot accommodate the plate current without excessive arcing.
LINEAR IMPEDANCE—An impedance in which a change in current through a device changes in direct proportion to the voltage applied to the device.
LOW-LEVEL MODULATION—Modulation produced in an earlier stage than the final.
LOW-PASS FILTER—A method of demodulating pdm by averaging the voltage over pulse and no-pulse time.
LOWER SIDEBAND—All difference frequencies below that of the carrier.
MACHINE KEYING—A method of cw keying using punched tape or other mechanical means to key a transmitter.
MAGNETIC MICROPHONE—A microphone in which the sound waves vibrate a moving armature. The armature consists of a coil wound on the armature and located between the pole pieces of a permanent magnet. The armature is mechanically linked to the diaphragm.
MARK—An interval during which a signal is present. Also the presence of an rf signal in cw keying. The key-closed condition (presence of data) in communications systems.
AI-4
MASTER OSCILLATOR POWER AMPLIFIER (MOPA)—A transmitter in which the oscillator is isolated from the antenna by a power amplifier.
MICROPHONE—An energy converter that changes sound energy into electrical energy.
MODULATED WAVE—A complex wave consisting of a carrier and a modulating wave that is transmitted through space.
MODULATING WAVE—An information wave representing intelligence.
MODULATION FACTOR (M)—An indication of relative magnitudes of the rf carrier and the audio-modulating signal.
MODULATION INDEX—The ratio of frequency deviation to the frequency of the modulating signal.
MODULATION—The ability to impress intelligence upon a transmission medium, such as radio waves.
MODULATOR—The last audio stage in which intelligence is applied to the rf stage to modulate the carrier.
MULTIPLICATION FACTOR—The number of times an input frequency is multiplied.
MULTIVIBRATOR MODULATOR—An astable multivibrator used to provide frequency modulation by inserting the modulating af voltage in series with the base-return of the multivibrator transistors.
NEGATIVE ALTERNATION—That part of a sine wave that is below the reference level.
NONLINEAR DEVICE—A device in which the output does not rise and fall directly with the input.
NONLINEAR IMPEDANCE—An impedance in which the resulting current through the device is not proportional to the applied voltage.
OVERMODULATION—A condition that exists when the peaks of the modulating signal are limited.
PEAK AMPLITUDE—The maximum value above or below the reference line.
PEAK DETECTION—Detection that uses the amplitude of pam or the duration of pdm to charge a holding capacitor and restore the original waveform.
PEAK POWER—The maximum value of the transmitted pulse.
PERCENT OF MODULATION—The degree of modulation defined in terms of the maximum permissible amount of modulation.
PERIOD—The duration of a waveform.
PHASE MODULATION (pm)—Angle modulation in which the phase of the carrier is controlled by the modulating waveform. The amplitude of the modulating wave determines the amount of phase shift and the frequency of the modulation determines how often the phase shifts.
AI-5
PHASE or PHASE ANGLE—The angle that exists between the starting point of a vector and its position at that instant. An indication of how much of a cycle has been completed at any given instant in time.
PHASE-SHIFT DISCRIMINATOR—See Foster-Seeley discriminator.
PHASE-SHIFT KEYING—Similar to ON-OFF cw keying in AM systems and frequency-shift keying in fm systems. Each time a mark is received, the phase is reversed. No phase reversal takes place when a space is received.
PLATE KEYING—A keying system in which the plate supply is interrupted.
PLATE MODULATOR—An electron-tube modulator in which the modulating voltage is applied to the plate circuit of the tube.
POSITIVE ALTERNATION—That part of a sine wave that is above the reference line.
PULSE DURATION (pd)—The period of time during which a pulse is present. PULSE MODULATION—A form of modulation in which one of the characteristics of a pulse
train is varied.
PULSE WIDTH (pw)—The period of time during which a pulse occurs. PULSE—A surge of plate current that occurs when a tube is momentarily saturated.
PULSE-AMPLITUDE MODULATION (pam)—Pulse modulation in which the amplitude of the pulses is varied by the modulating signal.
PULSE-CODE MODULATION (pcm)—A modulation system in which the standard values of a quantized wave are indicated by a series of coded pulses.
PULSE-DURATION MODULATION (pdm)—Pulse modulation in which the time duration of the pulses is changed by the modulating signal.
PULSE-FORMING NETWORK (pfn)—A circuit used for storing energy. Essentially a short section of artificial transmission line.
PULSE-FREQUENCY MODULATION (pfm)—Pulse modulation in which the modulating voltage varies the repetition rate of a pulse train.
PULSE-POSITION MODULATION (ppm)—Pulse modulation in which the position of the pulses is varied by the modulating voltage.
PULSE-REPETITION FREQUENCY—The rate, in pulses per second, at which the pulses occur.
PULSE-REPETITION TIME (prt)—The total time for one complete pulse cycle of operation (rest time plus pulse width).
PULSE-TIME MODULATION (ptm)—Pulse modulation that varies one of the time characteristics of a pulse train (pwm, pdm, ppm, and pfm).
PULSE-WIDTH MODULATION (pwm)—Pulse modulation in which the duration of the pulses is varied by the modulating voltage.
AI-6
PULSING—Allowing oscillations to occur for a specific period of time only during selected intervals.
QUANTIZED WAVE—A wave created by arbitrarily dividing the entire range of amplitude (or frequency, or phase) values of an analog wave into a series of standard values. Each sample takes the standard value nearest its actual value when modulated.
QUANTIZING NOISE—A distortion introduced by quantizing the signal. RADAR DETECTOR—A detector which, in its simplest form, only needs to be capable of
producing an output when rf energy (reflected from a target) is present at its input. RATIO DETECTOR—A detector that uses a double-tuned transformer to convert the
instantaneous frequency variations of the fm input signal to instantaneous amplitude variations.
RATIO OF TRANSMITTED POWERS—The power ratio (fsk verses AM) that expresses the overall improvement of fsk transmission when compared to AM under rapid-fading and high-noise conditions.
REACTANCE TUBE—A tube connected in parallel with the tank circuit of an oscillator. Provides a signal that will either lag or lead the signal produced by the tank.
REACTANCE-TUBE MODULATOR—An fm modulator that uses a reactance tube in parallel with the oscillator tank circuit.
REGENERATIVE DETECTOR—A detector circuit that produces its own oscillations, heterodynes them with an incoming signal, and detects them.
REST FREQUENCY—The carrier frequency during the constant-amplitude portions of a phase modulation signal.
REST TIME (rt)—The time when there is no pulse or nonpulse. ROTARY GAP—Similar to a mechanically driven switch. Used to discharge a pulse-forming
network.
SENSITIVITY OF A MICROPHONE—Efficiency of a microphone. Describes micro- phone power delivered to a matched-impedance load as compared to the sound level being converted. Usually expressed in terms of the electrical power level.
SERIES-DIODE DETECTOR—The semiconductor diode in series with the input voltage and the load impedance. Sometimes called a voltage-diode detector.
SHUNT—Means the same as parallel or to place in parallel with other components.
SHUNT-DIODE DETECTOR—A diode detector in which the diode is in parallel with the input voltage and the load impedance. Also known as a current detector because it operates with smaller input levels.
SIGNAL DISTORTION—Any unwanted change to the signal.
SIGNIFICANT SIDEBANDS—Those sidebands with significantly large amplitude.
AI-7
SINE WAVE—The basic synchronous alternating waveform for all complex waveforms.
SLOPE DETECTOR—A tank circuit tuned to a frequency, either slightly above or below an fm carrier frequency, that is used to detect intelligence.
SPACE—Absence of an rf signal in cw keying. Key-open condition or lack of data in communications systems. Also a period of no signal.
SPARK-GAP MODULATOR—Modulator consists of a circuit for storing energy, a circuit for rapidly discharging the storage circuit (spark gap), a pulse transformer, and a power source.
SPECTRUM ANALYSIS—The display of electromagnetic energy arranged according to wavelength or frequency.
SPLATTER—Unwanted sideband frequencies that are generated from overmodulation.
THYRATRON MODULATOR—An electronic switch that requires a low potential to turn it on.
TRANSMISSION MEDIUM—A means of transferring intelligence from point to point. Can be described as light, smoke, sound, wirelines, or radio-frequency waves.
UPPER SIDEBAND—All of the sum frequencies above the carrier.
VARACTOR—A diode, or pn junction, that is designed to have a certain amount of capacitance between junctions.
VARACTOR FM MODULATOR—An fm modulator which uses avoltage-variable capacitordiode (varactor).
VOLTAGE-DIODE DETECTOR—Series detector in which the crystal is in series with the input voltage and the load impedance.
VECTOR—Mathematical method of showing both magnitude and direction.
WAVELENGTH—The physical dimension of a sine wave.
INDEX-1
INDEX-2
Information: The text pages that you are to study are provided at the beginning of the assignment questions.
1
Textbook assignment: Chapter 1, “Amplitude Modulation,” pages 1-1 through 1-75. _________________________________________________________________________________
1-1. The action of impressing intelligence upon a transmission medium is referred to as
1. modulating 2. demodulating 3. heterodyning 4. wave generating
1-2. You can communicate with others using which of the following transmissions mediums?
1. Light 2. Wire lines 3. Radio waves 4. Each of the above
1-3. When you use a vector to indicate force in a diagram, what do (a) length and (b) arrowhead position indicate?
1. (a) Magnitude (b) direction 2. (a) Magnitude (b) frequency 3. (a) Phase (b) frequency 4. (a) Phase (b) direction
1-4. Vectors are used to show which of the following characteristics of a sine wave?
1. Fidelity 2. Amplitude 3. Resonance 4. Distortion
1-5. A rotating coil in the uniform magnetic field between two magnets produces a sine wave. It is called a sine wave because the voltage depends on which of the following factors?
1. The number of turns in the coil 2. The speed at which the coil is rotating 3. The angular position of the coil in the
magnetic field 4. Each of the above
1-6. The trigonometric relationship for the sine of an angle in a right triangle is figured using which of the following ratios?
1. Opposite side ÷ hypotenuse 2. Adjacent side ÷ hypotenuse 3. Hypotenuse ÷ opposite side 4. Hypotenuse ÷ adjacent side
1-7. The part of a sine wave that is above the voltage reference line is referred to as the
1. peak amplitude 2. positive alternation 3. negative alternation 4. instantaneous amplitude
1-8. The degree to which a cycle has been completed at any given instant is referred to as the
1. phase 2. period 3. frequency 4. amplitude
2
1-9. The frequency of the sine wave is determined by which of the following sine-wave factors?
1. The maximum voltage 2. The rate at which the vector rotates 3. The number of degrees of vector
rotation 4. Each of the above
1-10. Which of the following mathematical relationships do you use to figure the period of a sine wave?
1.
3.
2.
4.
1-11. Which of the following Greek letters is
the symbol for wavelength?
1. θ 2. ϑ 3. λ 4. ω
1-12. Which of the following waveform characteristics determines the wavelength of a sine wave?
1. Phase 2. Period 3. Amplitude 4. Phase Angle
1-13. An electromagnetic wavefront moves through free space at approximately what speed in meters per second?
1. 3,000,000 2. 30,000,000 3. 300,000,000 4. 3,000,000,000
1-14. What is the wavelength of a 1.5 MHz frequency?
1. 100 meters 2. 200 meters 3. 300 meters 4. 400 meters
1-15. As the frequency of a signal is increased, what change can be noted about its wavelength?
1. It decreases 2. It increases 3. It remains the same
1-16. The ability of a circuit to faithfully reproduce the input signal in the output is known by what term?
1. Fidelity 2. Fluctuation 3. Directivity 4. Discrimination
1-17. In rf communications, modulation impresses information on which of the following types of waves?
1. Carrier wave 2. Complex wave 3. Modulated wave 4. Modulating wave
1-18. Which of the following types of modulation is a form of amplitude modulation?
1. Angle 2. Phase 3. Frequency 4. Continuous-wave
3
1-19. With a sine-wave input, how will the output compare to the input in (a) a linear circuit and (b) a nonlinear circuit?
1. (a) Proportional
2. (a) Proportional (b) not proportional
3. (a) Not proportional (b) not proportional
4. (a) Not proportional (b) proportional
1-20. What effect, if any, does a nonlinear
device have on a sine wave?
1. It amplifies without distortion 2. It attenuates without distortion 3. It generates harmonic frequencies 4. None
1-21. For the heterodyning action to occur in a circuit, (a) what number of frequencies must be present and (b) to what type of circuit must they be applied?
1. (a) Two (b) linear 2. (a) Two (b) nonlinear 3. (a) Three (b) nonlinear 4. (a) Three (b) linear
1-22. Spectrum analysis is used to view which of the following characteristics of an rf signal?
1. Phase 2. Bandwidth 3. Modulating wave 4. Modulation envelope
1-23. The method of rf communication that uses either the presence or absence of a carrier in a prearranged code is what type of modulation?
1. Pulse modulation 2. Amplitude modulation 3. Continuous-wave modulation 4. Pulse-time modulation
1-24. What is the purpose of the key in a cw transmitter?
1. It generates the rf oscillations 2. It heterodynes the rf oscillations 3. It controls the rf output 4. It amplifies the rf signal
1-25. To ensure frequency stability in a cw transmitter, you should NOT key what circuit?
1. The mixer 2. The detector 3. The oscillator 4. The rf amplifier
1-26. When keying a high-power transmitter, what component should you use to reduce the shock hazard?
1. A coil 2. A relay 3. A resistor 4. A capacitor
1-27. Interference detected by a receiver is often caused by the application and removal of power in nearby transmitters. This interference can be prevented by using what type of circuit in such transmitters?
1. Power filter 2. On-off filter 3. Key-click filter 4. Rf detector filter
1-28. Transmitter machine keying was developed for which of the following purposes?
1. To increase the speed of
communications 2. To make communications more
intelligible 3. To reduce interference 4. Each of the above
4
1-29. Which of the following advantages is a benefit of cw communications?
1. Wide bandwidth 2. Fast transmission 3. Long-range operation 4. Each of the above
1-30. To prevent a transmitter from being loaded unnecessarily, where should you connect the antenna?
1. At the oscillator input 2. At the oscillator output 3. At the power-amplifier input 4. At the power-amplifier output
1-31. Amplifier tubes are added to the output of a transmitter for which of the following reasons?
1. To increase power 2. To increase frequency 3. To increase stability 4. To increase selectivity
1-32. Which of the following combinations of frequency multiplier stages will produce a total multiplication factor of 72?
1. 36, 36 2. 4, 3, 3, 2 3. 4, 4, 3, 2 4. 18, 18, 18, 18
1-33. To change sound energy into electrical energy, which of the following devices should you use?
1. A speaker 2. A microphone 3. An amplifier 4. An oscillator
1-34. Which of the following is the schematic symbol for a microphone?
1.
3.
2.
4.
1-35. What component in a carbon microphone converts a dc voltage into a varying current?
1. Button 2. Diaphragm 3. Transformer 4. Carbon granules
1-36. The action of the double-button carbon microphone is similar to which of the following electronic circuits?
1. A limiter 2. An oscillator 3. A voltage doulber 4. A push-pull amlifier
1-37. A carbon microphone has which of the following advantages over other types of microphones?
1. Ruggedness 2. Sensitivity 3. Low output voltage 4. Frequency response
1-38. The voltage produced by mechanical stress placed on certain crystals is a result of which of the following effects?
1. Hall 2. Acoustic 3. Electrostatic 4. Piezoelectric
5
1-39. If you require a microphone that is lightweight, has high sensitivity, is rugged, requires no external voltage, can withstand temperature, vibration, and moisture extremes, and has a uniform frequency response of 40 to 15,000 hertz, which of the following types of microphones should you select?
1. Carbon 2. Crystal 3. Dynamic 4. Electrostatic
1-40. What component in a magnetic microphone causes the lines of flux to alternate?
1. The coil 2. The magnet 3. The diaphragm 4. The armature
1-41. What are the two major sections of an AM transmitter?
1. Audio frequency unit and radio
frequency unit 2. Audio frequency unit and master
oscillator 3. Audio frequency unit and final power
amplifier 4. Audio frequency unit and
1-42. The intermediate power amplifier serves what function in a transmitter?
1. It generates the carrier 2. It modulates the carrier 3. It increases the frequency of the
signal 4. It increases the power level of the
1-43. The final audio stage in an AM transmitter is the
1. mixer 2. modulator 3. multipler 4. multiplexer
1-44. The vertical axis on a frequency- spectrum graph represents which of the following waveform characteristics?
1. Phase 2. Duration 3. Frequency 4. Amplitude
1-45. When a 500-hertz signal modulates a 1-megahertz carrier, the 1-megahertz carrier and what two other frequencies are transmitted?
1. 500 and 999,500 hertz 2. 500 and 1,000,500 hertz 3. 999,500 and 1,500,000 hertz 4. 999,500 and 1,000,500 hertz
1-46. If 750 hertz modulates a 100-kilohertz carrier, what would the upper-sideband frequency be?
1. 99,250 hertz 2. 100,000 hertz 3. 100,500 hertz 4. 100,750 hertz
1-47. In an AM wave, where is the audio intelligence located?
1. In the carrier frequency 2. In the spacing between the sideband
frequencies 3. In the spacing between the carrier and
sideband frequencies 4. In the sideband frequencies
6
1-48. What determines the bandwidth of an AM wave?
1. The carrier frequency 2. The number of sideband frequencies 3. The lowest modulating frequency 4. The highest modulating frequency
1-49. If an 860-kilohertz AM signal is modulated by frequencies of 5 and 10 kilohertz, what is the bandwidth?
1. 5 kilohertz 2. 10 kilohertz 3. 15 kilohertz 4. 20 kilohertz
1-50. If a 1-megahertz signal is modulated by frequencies of 50 and 75 kilohertz, what is the resulting maximum frequency range?
1. 925,000 to 1,000,000 hertz 2. 925,000 to 1,075,000 hertz 3. 975,000 to 1,025,000 hertz 4. 1,000,000 to 1,075,000 hertz
1-51. If an rf carrier is 100 percent AM- modulated, what will be the rf output when the modulating signal is (a) at its negative peak and (b) at its positive peak?
(a) 0 1. (b) 2 times the amplitude of the
unmodulated carrier 2. (a) 0
3.
4.
1-52. In an AM signal that is 100 percent modulated, what maximum voltage value is present in each sideband?
1. 1/4 the carrier voltage 2. 1/2 the carrier voltage 3. 3/4 the carrier voltage 4. Same as the carrier voltage
1-53. Overmodulation of an AM signal will have which, if any, of the following effects on the bandwidth?
1. It will increase 2. It will decrease 3. It will remain the same
1-54. In a carrier wave with a peak amplitude of 400 volts and a peak modulating voltage of 100 volts, what is the modulation factor?
1. 0.15 2. 0.25 3. 0.45 4. 0.55
1-55. The percent of modulation for a modulated carrier wave is figured using which of the following formulas?
1.
3.
2.
4.
1-56. Modulation produced in the plate circuit of the last radio stage of a system is known by what term?
1. Low-level modulation 2. High-level modulation 3. Final-amplifier modulation 4. Radio frequency modulation
7
1-57. Which, if any, of the following advantages is a primary benefit of plate modulation?
1. It operates at low efficiency 2. It operates at low power levels 3. It operates with high efficiency 4. None of the above
1-58. A final rf power amplifier biased for plate modulation operates in what class of operation?
1. A 2. B 3. AB 4. C
1-59. Heterodyning action in a plate modulator takes place in what circuit?
1. Grid 2. Plate 3. Screen 4. Cathode
1-60. A plate modulator produces a modulated rf output by controlling which of the following voltages?
1. Plate voltage 2. Cathode voltage 3. Grid-bias voltage 4. Grid-input voltage
1-61. To achieve 100-percent modulation in a plate modulator, what maximum voltage must the modulator tube be capable of providing to the final power amplifier (fpa)?
1. Twice the fpa plate voltage 2. The same as the fpa plate voltage 3. Three times the fpa plate voltage 4. Half the fpa plate voltage
1-62. In a plate modulator, with no modulation, how will the plate current of the final rf amplifier appear on a scope?
1. A series of pulses at the carrier
frequency 2. A series of pulses at twice the carrier
frequency 3. A series of pulses at 1/4 the carrier
frequency 4. A series of pulses at 1/2 the carrier
1-63. In the collector-injection modulator, af and rf are heterodyned by injecting the rf into (a) what circuit and the af into (b) what circuit?
1. (a) Base (b) collector 2. (a) Base (b) emitter 3. (a) Emitter (b) collector 4. (a) Emitter (b) base
1-64. Plate- and collector-injection modulators are the most commonly used modulators for which of the following reasons?
1. The rf amplifier stages can be
operated class C for linearity 2. The rf amplifier stages can be
3. They require small amounts of audio power
4. They require large amounts of audio power
1-65. A control-grid modulator would be used
in which of the following situations?
1. In extremely high-power, wideband equipment where high-level modulation is difficult to achieve
2. In cases where the use of a minimum of audio power is desired
3. In portable and mobile equipment to reduce size and power requirements
4. Each of the above
8
1-66. Which of the following inputs is/are applied to the grid of a control-grid modulator?
1. Rf 2. Af 3. Dc bias 4. Each of the above
1-67. Excessive modulating signal levels have which, if any, of the following effects on a control-grid modulator?
1. They increase output. amplitude 2. They decrease output amplitude 3. They create distortion 4. None
1-68. Compared to a plate modulator, the control-grid modulator has which of the following advantages?
1. It is more efficient 2. It has less distortion 3. It requires less power from the
modulator 4. It requires less power from the
1-69. The control-grid modulator is similar to which of the following modulator circuits?
1. Plate 2. Cathode 3. Base-injection 4. Emitter-injection
Figure 1A.—Modulator circuit.
IN ANSWERING QUESTIONS 1-70 THROUGH 1-72, REFER TO FIGURE 1A.
1-70. What components in the circuit establish
the bias for Q1?
1. R1 and R2 2. R2 and R3 3. R1 and R3
1-71. The rf voltage in the circuit is applied at (a) what points and the af voltage is applied at (b) what points?
1. (a) A and B (b) C and D 2. (a) C and D (b) A and B 3. (a) C and D (b) E and F 4. (a) E and F (b) C and D
1-72. What components develop the rf modulation envelope?
1. C1 and R1 2. C2 and R1 3. C3 and R3 4. C4 and L1
9
1-73. A cathode modulator is used in which of the following situations?
1. When rf power is unlimited and
distortion can be tolerated 2. When rf power is limited and
distortion cannot be tolerated 3. When af power is unlimited and
distortion can be tolerated 4. When af power is limited and
distortion cannot be tolerated 1-74. In a cathode modulator, the modulating
voltage is in series with which of the following voltages?
1. The grid voltage only 2. The plate voltage only 3. Both the grid and plate voltages 4. The cathode voltage only
Figure 1B.—Emitter-injection modulator.
IN ANSWERING QUESTION 1-75, REFER TO FIGURE 1B. 1-75. In the circuit, what components develop
the modulation envelope?
1. Q1 2. C2 and R1 3. C3 and R3 4. C4 and L1
10
ASSIGNMENT 2 Textbook assignment: Chapter 2, “Angle and Pulse Modulation,” pages 2-1 through 2-64.
2-1. Frequency-shift keying resembles what type of AM modulation?
1. CW modulation 2. Analog AM modulation 3. Plate modulation 4. Collector-injection modulation
2-2. Frequency-shift keying is generated using which of the following methods?
1. By shifting the frequency of an oscillator at an af rate
2. By shifting the frequency of an oscillator at an rf rate
3. By keying an af oscillator at an rf rate 4. By keying an af oscillator at an af rate
2-3. In a frequency-shift keyed signal, where is the intelligence contained?
1. In the duration of the rf energy 2. In the frequency of the rf energy 3. In the amplitude of the rf energy 4. In the spacing between bursts of rf
2-4. If an fsk transmitter has a MARK frequency of 49.575 kilohertz and a SPACE frequency of 50.425 kilohertz, what is the assigned channel frequency?
1. 49 kilohertz 2. 49.575 kilohertz 3. 50 kilohertz 4. 50.425 kilohertz
2-5. Fsk is NOT affected by noise interference for which of the following reasons?
1. Noise is outside the bandwidth of an fsk signal
2. Fsk does not rely on the amplitude of the transmitted signal to carry intelligence
3. The wide bandwidth of an fsk signal prevents noise interference
4. Each of the above
2-6. In an fsk transmitter, what stage is keyed?
1. The oscillator 2. The power supply 3. The power amplifier 4. The buffer amplifier
2-7. When the amount of oscillator frequency shift in an fsk transmitter is determined, which of the following factors must be considered?
1. The number of buffer amplifiers 2. The transmitter power output 3. The frequency multiplication factor for
the transmitter amplifiers 4. The oscillator rest frequency
2-8. In an fsk transmitter with a doubler and a tripler stage, the desired frequency shift is 1,200 hertz. To what maximum amount is the oscillator frequency shift limited?
1. 60 hertz 2. 100 hertz 3. 120 hertz 4. 200 hertz
11
2-9. Fsk has which of the following advantages over cw?
1. Fsk has a more stable oscillator 2. Fsk is easier to generate 3. Fsk rejects unwanted weak signals 4. Fsk does not have noise in its output
2-10. The "ratio of transmitted powers" provides what information?
1. Transmitter power out in a cw system 2. Transmitter power out in an fsk system 3. Improvement shown using cw instead
of fsk transmission 4. Improvement shown using fsk instead
2-11. In an fm signal, (a) the RATE of shift is proportional to what characteristic of the modulating signal, and (b) the AMOUNT of shift is proportional to what characteristic?
1. (a) Amplitude (b) amplitude 2. (a) Amplitude (b) frequency 3. (a) Frequency (b) frequency 4. (a) Frequency (b) amplitude
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IN ANSWERING QUESTIONS 2-12 THROUGH 2-14, REFER TO FIGURE 2A.
2-12. When a sound wave strikes the condenser microphone (M), it has which, if any, of the following effects on the oscillator circuit?
1. It changes output phase 2. It changes output voltage 3. It changes output frequency 4. It has no effect
2-13. What is the purpose of capacitor C in the circuit?
1. It helps set the carrier frequency of the oscillator
2. It prevents amplitude variations in the oscillator output
3. It sets the maximum frequency deviation of the oscillator
4. It varies the output frequency in accordance with the modulating voltage
12
2-14. A 1,000-hertz tone of a certain loudness causes the frequency-modulated carrier for the circuit to vary – 1,000 hertz at a rate of 1,000 times per second. If the AMPLITUDE of the modulating tone is doubled, what will be the maximum carrier variation?
1. – 1,000 hertz at 1,000 times per second 2. – 1,000 hertz at 2,000 times per second 3. – 2,000 hertz at 1,000 times per second 4. – 2,000 hertz at 2,000 times per second
2-15. The maximum deviation for a 1.5 MHz carrier is set at – 50 kHz. If the carrier varies between 1.5125 MHz and 1.4875 MHz ( – 12.5 kHz), what is the percentage of modulation?
1. 25 % 2. 50 % 3. 75 % 4. 100 %
2-16. An fm transmitter has a 50-watt carrier with no modulation. What maximum amount of output power will it have when it is 50-percent modulated?
1. 25 watts 2. 50 watts 3. 75 watts 4. 100 watts
2-17. Frequencies that are located between adjacent channels to prevent interference are referred to as
1. sidebands 2. bandwidths 3. guard bands 4. blank channels
2-18. Modulation index may be figured by using which of the following formulas?
1. 2f/fm 2. fm/2f 3. fm/ D f 4. D f/fm
2-19. A 50-megahertz fm carrier varies between 49.925 megahertz and 50.075 megahertz 10,000 times per second. What is its modulation index?
1. 5 2. 10 3. 15 4. 20
IN ANSWERING QUESTIONS 2-20 AND 2-21, REFER TO FIGURE 2B.
2-20. An fm-modulated carrier varies between 925 kilohertz and 1,075 kilohertz 15,000 times per second. What is the bandwidth, in kilohertz, of the transmitted signal? (HINT: You will need to figure MI to be able to find the sidebands.)
1. 340 2. 420 3. 480 4. 560
13
2-21. The spectrum of a 500 kilohertz fm- modulated carrier has a 60-kilohertz bandwidth and contains 12 significant sidebands. How much, in kilohertz, is the carrier deviated?
1. – 5 2. – 7.5 3. – 10 4. – 15
2-22. In a reactance-tube modulator, the reactance tube shunts what part of the oscillator circuitry?
1. The amplifier 2. The tank circuit 3. The biasing network 4. The feedback network
2-23. With no modulating signal applied, a reactance tube has which, if any, of the following effects on the output of an oscillator?
1. It will decrease amplitude 2. It will increase amplitude 3. It will change resonant frequency 4. It will have no effect
2-24. The reactance-tube frequency modulates the oscillator by which of the following actions?
1. By shunting the tank circuit with a variable resistance
2. By shunting the tank circuit with a variable reactance
3. By shunting the tank circuit with a variable capacitance
4. By causing a resultant current flow in the tank circuit which either leads or lags resonant current
IN ANSWERING QUESTIONS 2-25 AND 2-26, REFER TO FIGURE 2C.
2-25. The semiconductor reactance modulator in the circuit is in parallel with a portion of the oscillator tank circuit coil. Modulation results because of interaction with which of the following transistor characteristics?
1. Collector-to-emitter resistance 2. Collector-to-emitter capacitance 3. Base-to-emitter resistance 4. Base-to-emitter capacitance
2-26. With a positive-going modulating signal applied to the base of Q2, (a) what will circuit capacitance do and (b) what will the output frequency do?
1. (a) Decrease (b) decrease 2. (a) Decrease (b) increase 3. (a) Increase (b) increase 4. (a) Increase (a) decrease
14
2-27. What type of circuit is used to remove the AM component in the output of a semiconductor reactance modulator?
1. A mixer 2. A filter 3. A limiter 4. A buffer amplifier
IN ANSWERING QUESTIONS 2-28 AND 2-29, REFER TO FIGURE 2D.
2-28. The multivibrator modulator produces fm modulation by which of the following actions?
1. By modulating the collector voltages 2. By modulating the base-return voltages 3. By modulating the value of the base
value of the base capacitors 4. By modulating the value of the base
2-29. What is the purpose of the filter on the output of the multivibrator modulator?
1. To establish the fundamental operating frequency
2. To eliminate unwanted frequency variations
3. To eliminate unwanted odd harmonics 4. To eliminate unwanted even harmonics
2-30. A multivibrator frequency modulator is limited to frequencies below what maximum frequency?
1. 1 megahertz 2. 2 megahertz 3. 5 megahertz 4. 10 megahertz
2-31. To ensure the frequency stability of an fm transmitter, which, if any, of the following actions could be taken?
1. Modulate a crystal-controlled oscillator at the desired frequency
2. Modulate a low-frequency oscillator, and use frequency multipliers to achieve the operating frequency
3. Modulate a low-frequency oscillator, and heterodyne it with a higher- frequency oscillator to achieve the desired frequency
4. None of the above
2-32. A varactor is a variable device that acts as which of the following components?
1. Resistor 2. Inductor 3. Capacitor 4. Transistor
2-33. As the positive potential is increased on the cathode of a varactor, (a) what happens to reverse bias and (b) how is dielectric width affected?
1. (a) Increases (b) increases 2. (a) Increases (b) decreases 3. (a) Decreases (b) decreases 4. (a) Decreases (b) increases
15
IN ANSWERING QUESTION 2-34, REFER TO FIGURE 2E.
2-34. In the figure, (a) waveform X has what phase relationship to waveform Y, and (b) waveform Y has what relationship to waveform Z?
1. (a) Lags (b) leads 2. (a) Lags (b) lags 3. (a) Leads (b) lags 4. (a) Leads (b) leads
2-35. A 10 kilohertz, 10-volt square wave is applied as the phase-modulating signal to a transmitter with a carrier frequency of 60 megahertz. What is the output frequency during the constant-amplitude portions of the modulating signal?
1. 10 kilohertz 2. 59,990 kilohertz 3. 60,000 kilohertz 4. 60,010 kilohertz
2-36. In a phase modulator, the frequency during the constant-amplitude portion of the modulating wave is the
1. peak frequency 2. rest frequency 3. deviation frequency 4. modulating frequency
2-37. In phase modulation, (a) the AMPLITUDE of the modulating signal determines what characteristic of the phase shift, and (b) the FREQUENCY of the modulating signal determines what characteristic of the phase shift?
1. (a) Rate (b) rate 2. (a) Rate (b) amount 3. (a) Amount (b) amount 4. (a) Amount (b) rate
2-38. The frequency spectrums of a phase- modulated signal resemble the spectrum of which, if any, of the following types of modulation?
1. Amplitude modulated 2. Frequency modulated 3. Continuous-wave modulated 4. None of the above
2-39. Compared to fm, increasing the modulating frequency in phase modulation has what effect, if any, on the bandwidth of the phase-modulated signal?
1. It increases 2. It decreases 3. None
2-40. A simple phase modulator consists of a capacitor in series with a variable resistance. What total amount of carrier shift will occur when X
C is 10 times the resistance?
1. 0 degrees 2. 45 degrees 3. 60 degrees 4. 90 degrees
2-41. The primary advantage of phase modulation over frequency modulation is that phase modulation has better carrier
1. power stability 2. amplitude stability 3. frequency stability 4. directional stability
16
2-42. Phase-shift keying is most useful under which of the following code element conditions?
1. When mark elements are longer than space elements
2. When mark elements are shorter than space elements
3. When mark and space elements are the same length
4. When mark and space elements are longer than synchronizing elements
2-43. When a carrier is phase-shift keying modulated, (a) a data bit ONE will normally cause the carrier to shift its phase what total number of degrees, and (b) a data bit ZERO will cause the carrier to shift its phase what total number of degrees?
1. (a) 60 (b) 0 2. (a) 0 (b) 180 3. (a) 180 (b) 180 4. (a) 180 (b) 0
2-44. Which of the following circuits is used to generate a phase-shift keyed signal?
1. Logic circuit 2. Phasor circuit 3. Phasitron circuit 4. Longitudinal circuit
2-45. When a carrier is modulated by a square wave, what maximum number of sideband pairs will be generated?
1. 1 2. 9 3. 3 4. An infinite number
2-46. As the square wave modulating voltage is increased to the same amplitude as that of the carrier, what will be the effect on (a) the carrier amplitude and (b) amplitude of the sidebands?
1. (a) Remains constant (b) Increases
2. (a) Decreases (b) Increases
3. (a) Increases (b) Remains constant
4. (a) Increases (b) Decreases
2-47. In a square-wave modulated signal, total sideband power is what percentage of the total power?
1. 0 percent 2. 25 percent 3. 33 percent 4. 50 percent
IN ANSWERING QUESTIONS 2-48 THROUGH 2-51, REFER TO FIGURE 2F. SELECT THE FIGURE LETTER THAT CORRESPONDS WITH THE WAVEFORM LISTED IN THE QUESTIONS. LETTERS MAY BE USED ONCE, MORE THAN ONCE, OR NOT AT ALL.
2-48. Pulse width.
1. A 2. B 3. C 4. D
17
2-49. Rest time.
1. B 2. C 3. D 4. E
2-50. Pulse duration.
1. A 2. B 3. D 4. E
2-51. Pulse-repetition time.
1. B 2. C 3. D 4. E
2-52. Which of the following ratios is used to determine pulse-repetition frequency (prf)?
1. 3.
2. 4.
2-53. Average power in a pulse-modulation system is defined as the
1. power during rest time 2. power during each pulse 3. power during each pulse averaged over
rest time 4. power during each pulse averaged over
2-54. In pulse modulation, what term is used to indicate the ratio of time the system is actually producing rf?
1. Rest cycle 2. Duty cycle 3. Average cycle 4. Transmit cycle
2-55. In a pulse-modulation system, which of the following formulas is used to figure the percentage of transmitting time?
1. 3.
2. 4.
2-56. When pulse modulation is used for range finding in a radar application, which of the following types of pulse information is used?
1. Reflected pulse return interval 2. Reflected pulse duration 3. Reflected pulse amplitude 4. Reflected pulse frequency
2-57. In a spark-gap modulator, what is the function of the pulse-forming network?
1. To store energy 2. To increase the level of stored energy 3. To act as a power bleeder 4. To rapidly discharge stored energy
2-58. The damping diode in a thyratron modulator serves which of the following purposes?
1. It discharges the pulse-forming network
2. It limits the input signal 3. It prevents the breakdown of the
thyratron by reverse-voltage transients 4. It rectifies the input signal
2-59. Compared to a spark-gap modulator, the thyratron modulator exhibits which of the following advantages?
1. Improved timing 2. Higher output pulses 3. Higher trigger voltage 4. Operates over a narrower range of
18
2-60. To transmit intelligence using pulse modulation, which of the following pulse characteristics may be varied?
1. Pulse duration 2. Pulse amplitude 3. Pulse-repetition time 4. Each of the above
2-61. To accurately reproduce a modulating signal in a pulse-modulated system, what minimum number of samples must be taken per cycle?
1. One 2. Two 3. Three 4. Four
2-62. What is the simplest form of pulse modulation?
1. Pulse-code modulation 2. Pulse-duration modulation 3. Pulse-frequency modulation 4. Pulse-amplitude modulation
2-63. The same pulse characteristic is varied in which of the following types of pulse modulations?
1. Pam and pdm 2. Pdm and pwm 3. Pwm and ppm 4. Ppm and pam
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IN ANSWERING QUESTION 2-64, REFER TO FIGURE 2G.
2-64. Which of the points shown in the waveform may be varied in pulse-duration modulation?
1. A only 2. B only 3. C only 4. A and/or C
2-65. Which, if any, of the following is the primary disadvantage of pulse-position modulation?
1. It depends on transmitter-receiver synchronization
2. It is susceptible to noise interference 3. Transmitter power varies 4. None of the above
2-66. A pfm transmitter transmits 10,000 pulses per second without a modulating signal applied. How, if at all, will a modulating signal affect the transmitted pulse rate?
1. It will decrease the transmitted pulse rate
2. It will increase the transmitted pulse rate
3. Both 1 and 2 above 4. It will not affect the transmitted pulse
19
2-67. The process of arbitrarily dividing a wave into a series of standard values is referred to as
1. arbitration 2. quantization 3. interposition 4. approximation
2-68. A pcm system is capable of transmitting 32 standard levels that ate sampled 2.5 times per cycle of a 3-kilohertz modulating signal. What maximum number of bits per second are transmitted?
1. 18,750 2. 37,500 3. 75,000 4. 240,000
2-69. Which of the following is a characteristic of a pcm system that makes it advantageous for use in multiple-relay link systems?
1. Average power is constant 2. Average power decreases with each
relay 3. Noise is not cumulative at relay
stations 4. Quantization noise decreases with each
20
Textbook assignment: Chapter 3, “Demodulation,” pages 3-1 through 3-35. _________________________________________________________________________________
3-1. The process of recreating the original modulating frequencies (intelligence) from an rf carrier is known by which of the following terms?
1. Detection 2. Demodulation 3. Both 1 and 2 above 4. Distribution
3-2. When a demodulator fails to accurately recover intelligence from a modulated carrier, which of the following types of distortion result?
1. Phase 2. Frequency 3. Amplitude 4. Each of the above
3-3. In a demodulator circuit, which of the following components is required for demodulation to occur?
1. A linear device 2. A nonlinear device 3. A variable resistor
3-4. In cw demodulation, the first requirement of the circuit is the ability to detect
1. the presence or absence of the carrier 2. amplitude variations in the carrier 3. frequency variations in the carrier 4. phase variations in the carrier
Figure 3A.—Cw demodulation.
IN ANSWERING QUESTION 3-5, REFER TO FIGURE 3A.
3-5. In the figure, L and C1 form a frequency- selective network that serves what purpose?
1. It removes the carrier 2. It rectifies the oscillations 3. It tunes the circuit to the desired rf
carrier 4. It provides filtering to maintain a
3-6. To aid in distinguishing between two or more cw signals that are close to the same frequency, which of the following detectors is used?
1. Diode 2. Crystal 3. Heterodyne 4. Transistor
21
3-7. Assume that two signals are received, one at 500 kHz and the other at 501 kHz. What frequency, in kHz, should be mixed with them to distinguish the 501 kHz signal by producing a 1 kHz output?
1. 499 2. 500 3. 501 4. 502
3-8. The detector circuit in the figure uses the heterodyning principle to detect the incoming signal. What type of detector is it?
1. Hartley 2. Colpitts 3. Armstrong 4. Regenerative
3-9. What component controls the operating frequency of the detector?
1. C1 2. C2 3. L2 4. R1
3-10. What component provides the feedback necessary for oscillations to occur?
1. R1 2. C2 3. C3 4. L2
3-11. Which of the following circuit functions
does Q1 perform?
1. Mixer 2. Detector 3. Oscillator 4. Each of the above
3-12. A circuit that is nonlinear, provides filtering, and is sensitive to the type of modulation applied to it fulfills the requirements of which, if any, of the following circuits?
1. Mixer 2. Modulator 3. Demodulator 4. None of the above
3-13. A detector uses which of the following signals to approximate the original waveform?
1. The sum frequency 2. The carrier frequency 3. The modulation envelope
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22
Figure 3C.—Detector.
IN ANSWERING QUESTIONS 3-14 THROUGH 3-16, REFER TO FIGURE 3C. 3-14. What type of detector is shown in the
figure?
1. Series-diode 2. Parallel-diode 3. Inductive-diode 4. Capacitive-diode
3-15. What is the purpose of C1 and L?
1. To smooth the incoming rf 2. To select the desired af signal 3. To select the desired rf signal 4. To smooth the detected af signal
3-16. What is the purpose of C2?
1. To smooth the incoming rf signal 2. To select the desired af signal 3. To select the desired rf signal 4. To smooth the detected af signal
3-17. A shunt diode circuit is used as a detector in which of the following instances?
1. When a large input signal is supplied 2. When a large output current is
required 3. When the input signal variations
overdrive the audio amplifier stages 4. When the input signal variations are
Figure 3D.—Detector.
IN ANSWERING QUESTIONS 3-18 THROUGH 3-21, REFER TO FIGURE 3D. 3-18. What type of detector is shown in the
figure?
1. Ratio 2. Common-base 3. Regenerative 4. Common-emitter
3-19. What circuit component acts as the load for the detected audio?
1. R1 2. R2 3. R3 4. R4
3-20. What is the purpose of C4?
1. Tp bypass af 2. To bypass rf 3. To remove power supply voltage
variations 4. To determine the operating frequency
3-21. This detector circuit is used under which of the following circuit conditions?
1. When higher frequencies are used 2. When the best possible frequency
selection is required 3. When weak signals need to be
detected 4. When strong signals need to be
23
Figure 3E.—Circuit.
IN ANSWERING QUESTIONS 3-22 THROUGH 3-24, REFER TO FIGURE 3E. 3-22. What type of Circuits is/are shown in the
figure?
1. A detector 2. An amplifier 3. Both 1 and 2 above 4. An oscillator
3-23. What is the purpose of T2?
1. To filter rf 2. To filter af 3. To couple the af output 4. To couple the rf output
3-24. What is the function of C1 and R1?
1. To act as an integrator 2. To act as a frequency-selective
network 3. To act as a filter network 4. To act as a differentiator
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24
Figure 3F.—Foster-Seeley discriminator.
IN ANSWERING QUESTIONS 3-25 THROUGH 3-30, REFER TO FIGURE 3F. 3-25. In the figure, what is the purpose of Q1?
1. To act as a limiter only 2. To act as an amplifier only 3. To act as a limiter and an amplifier 4. To act as an oscillator
3-26. To what frequency are C1/L1 and C2/L2 tuned?
1. The af input 2. The center frequency of fm signal 3. The lowest fm deviation frequency 4. The highest fm deviation frequency
3-27. What is the function of L3?
1. To couple af to the output 2. To couple rf from the tank circuits to
CR1 and CR2 3. To prevent af from being coupled to
the power supply 4. To provide the dc return path for CR1
3-28. At resonance, what is the amplitude of e3 compared to e4?
1. e3 is less than e4 2. e3 is equal to e4 3. e3 is greater than e4
25
3-29. When the circuit is operating ABOVE resonance, (a) does inductive reactance increase or decrease, and (b) does capacitive reactance increase or decrease?
1. (a) Increases (b) increases 2. (a) Increases (b) decreases 3. (a) Decreases (b) decreases 4. (a) Decreases (b) increases
3-30. Circuit operation BELOW resonance is represented by which of the following vector diagrams?
1.
2.
3.
THIS SPACE LEFT BLANK INTENTIONALLY.
26
Figure 3G.—Ratio detector.
IN ANSWERING QUESTIONS 3-31 THROUGH 3-40, REFER TO FIGURE 3G. 3-31. To what frequency(ies) are (a) L1 and C1
and (b) L2 and C2 tuned?
1. (a) Center frequency (b) lower frequency limit
2. (a) Center frequency (b) center frequency
3. (a) Lower frequency limit (b) center frequency
4. (a) Lower frequency limit (b) lower frequency limit
3-32. What circuit filtering function do R5, C6,
and C7 provide?
1. Low-pass 2. High-pass 3. Band-pass 4. Band-reject
3-33. At resonance, what type of circuit does the tank circuit appear to be?
1. Reactive 2. Resistive 3. Inductive 4. Capacitive
3-34. At resonance, what is the phase relationship between tank current and primary voltage?
1. Tank current leads primary voltage by
90 degrees 2. Tank current lags primary voltage by
90 degrees 3. Tank current and primary voltage are
in phase 4. Tank current and primary voltage are
3-35. At resonance, what relative amount of conduction takes place through CR1 compared to that for CR2?
1. CR1 conducts more than CR2 2. CR1 conducts less than CR2 3. CR1 and CR2 conduct the same
3-36. At resonance, (a) will the charges on C3 and C4 be equal or unequal, and (b) will their polarities be the same or opposite? 1. (a) Equal (b) same 2. (a) Equal (b) opposite 3. (a) Unequal (b) opposite 4. (a) Unequal (b) same
3-37. ABOVE resonance, both voltages e1 and
e 2 have specific phase shift relationships to voltage e in that they either shift nearer to or farther from the phase of ep. What are the phase relationships between (a) e1 and ep and (b) e2 and ep?
1. (a) e1 is nearer to ep
(b) e2 is nearer to ep 2. (a) e1 is nearer to ep
(b) e2 is farther from ep 3. (a) e1 is farther from ep
(b) e2 is nearer to ep 4. (a) e1 is farther from ep
27
3-38. If C3 is charged to 6 volts and C4 is charged to 4 volts, what is the output voltage? 1. 1 volt 2. 2 volts 3. 3 volts 4. 4 volts
3-39. When operating BELOW resonance, what is the relationship of the vector sum of e 1 and ep to the vector sum of e2 and ep?
1. The sum of e1 and ep is larger than the
sum of e2 and ep 2. The sum of e1 and ep is smaller than
the sum of e2 and ep 3. The slam of e1 and ep is equal to the
3-40. What components help to reduce the effects of amplitude variations at the input of the circuit?
1. R1, R2, and C5 2. R5, C6, and C7 3. R1, R2, C3, and C4 4. L1, L2, L3, and C2
3-41. What is the minimum input voltage, in millivolts, required for a ratio detector?
1. 100 2. 200 3. 300 4. 400
3-42. Which of the following circuit functions is performed by the gated-beam detector?
1. Limiter 2. Detector 3. Amplifier 4. Each of the above
THIS SPACE LEFT BLANK INTENTIONALLY.
28
Figure 3H.—Gated-beam detector.
IN ANSWERING QUESTIONS 3-43 THROUGH 3-47, REFER TO FIGURE 3H. 3-43. What components in the circuit are used
to set the reference frequency for a gated- beam detector?
1. C1 and L1 2. C2 and L2 3. C3 and L3 4. C4 and R1
3-44. What tube pins connect to elements that perform in a manner similar to an AND gate in a digital device?
1. Pins 1 and 3 2. Pins 3 and 4 3. Pins 3 and 5 4. Pins 4 and 5
3-45. What type of tank circuit is the quadrature tank (L3 and C3)?
1. Low-Q 2. High-Q 3. Nonresonant 4. Series-resonant
3-46. For plate current to flow, what must be the polarities of (a) the quadrature grid and (b) the limiter grid?
1. (a) Negative (b) negative 2. (a) Negative (b) positive 3. (a) Positive (b) positive 4. (a) Positive (b) negative
3-47. ABOVE the center frequency of the received fm signal, (a) will the tank appear capacitive or inductive, and (b) will the average plate current increase or decrease?
1. (a) Inductive (b) increase 2. (a) Inductive (b) decrease 3. (a) Capacitive (b) decrease 4. (a) Capacitive (b) increase
3-48. To demodulate a phase-modulated signal, which, if any, of the following types of demodulators may be used?
1. Peak 2. Quadrature 3. Series-diode 4. None of the above
3-49. Which of the following circuits can be used as a communications pulse demodulator?
1. Conversion 2. Peak detector 3. Low-pass filter 4. Each of the above
THIS SPACE LEFT BLANK INTENTIONALLY.
29
Figure 3I.—Detector.
IN ANSWERING QUESTIONS 3-50 THROUGH 3-52, REFER TO FIGURE 3I. 3-50. To detect pulse-amplitude modulation,
what value must the RC time constant of R1 and C1 in the circuit be?
1. Five times the pulse width 2. Ten times the pulse width 3. Five times the interpulse period 4. Ten times the interpulse period
3-51. Which, if any, of the following functions is the purpose of CR2? 1. To quickly discharge C1 between
received pulses 2. To rectify input pulses 3. To clamp the output to a positive
level 4. None of the above
3-52. What change must be made to the circuit to detect pulse-duration modulation?
1. Remove R1 2. Increase the value of R1 3. Decrease the value of R1 4. Add a resistor in series with CR1
3-53. When a pulse-duration modulated signal is determined by using a low-pass filter, what characteristic of the signal is used?
1. Width 2. Amplitude 3. Frequency 4. Pulse position
3-54. To detect pulse-duration modulation, the
1. carrier frequency 2. intermediate frequency 3. pulse-repetition frequency 4. desired modulating frequency
3-55. What type(s) of modulation is/are normally detected by first converting it/them to another type of modulation?
1. Ppm only 2. Pfm only 3. Pcm only 4. Ppm, pfm, and pcm
3-56. What type of circuit can be used to convert from ppm to pdm for demodulation?
1. An amplifier 2. A flip-flop 3. An oscillator 4. A transformer
THIS SPACE LEFT BLANK INTENTIONALLY.
30
Figure 3J.—Pcm conversion.
IN ANSWERING QUESTIONS 3-57 THROUGH 3-59, REFER TO FIGURE 3J. 3-57. To convert from pcm to pam, what type
of circuit is used to apply the pcm to the input of the circuit shown?
1. A constant-current source 2. A constant-voltage source 3. A limiter-amplifier source 4. An oscillator-amplifier source
3-58. If C1 is allowed to charge 16 volts during the period of one pulse, each additional pulse increases the charge by 16 volts. With the binary-coded equivalent of an analog 12 applied to the input, what will be the output of the circuit at sampling time?
1. 10 volts 2. 12 volts 3. 14 volts 4. 16 volts
3-59. Between pulses, R1 must allow C1 to
discharge to what voltage?
1. 0 volts 2. One fourth of the charge on C1 3. One half of the charge on C1 4. Three fourths of the charge on C1


--- title: "PLANNING AND PLANTING YOUR GARDEN FROM SEED" date: "2000-01-01 20:12:17 -06:00" categories: - adult subtitle: "" layout: "events" event-image: "Sprouts.jpg" event-dates: "THURSDAY, DECEMBER 17" event-location: "Online via Zoom" button-type: "register" tickets-link: "https://55218.blackbaudhosting.com/55218/Planning-and-Planting-Your-Garden-with-Seeds" registration-info: "" instructor-info: "Red Butte Garden Greenhouse Grower, Kara Hastings" member-cost: "$30" public-cost: "$35" event-notes: "online" tickets-button: "" published: false ---
THURSDAY, DECEMBER 17
6-7:30PM
REGISTRATION REQUIRED
Online class registration includes one free admission pass to Red Butte Garden.
Are you thinking about starting a vegetable garden but don't know where to begin? Start right here! RBG greenhouse Grower, Kara Hastings, will walk you through the steps from layout to seeding. Learn the basics of how to choose the right plants for you (and Utah!), maximize your garden space, and get your veggies started.


# Copyright 2017-2022 John Snow Labs
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""Contains classes concerning ViTForImageClassification."""
from sparknlp.common import *
[docs]class ViTForImageClassification(AnnotatorModel,
HasBatchedAnnotateImage,
HasImageFeatureProperties,
HasEngine):
"""Vision Transformer (ViT) for image classification.
ViT is a transformer based alternative to the convolutional neural networks usually
used for image recognition tasks.
Pretrained models can be loaded with ``pretrained`` of the companion object:
.. code-block:: python
imageClassifier = ViTForImageClassification.pretrained() \\
.setInputCols(["image_assembler"]) \\
.setOutputCol("class")
The default model is ``"image_classifier_vit_base_patch16_224"``, if no name is
provided.
For available pretrained models please see the
`Models Hub <https://sparknlp.org/models?task=Image+Classification>`__.
Models from the HuggingFace 🤗 Transformers library are also compatible with Spark
NLP 🚀. To see which models are compatible and how to import them see
https://github.com/JohnSnowLabs/spark-nlp/discussions/5669 and to see more extended
examples, see
`ViTImageClassificationTestSpec <https://github.com/JohnSnowLabs/spark-nlp/blob/master/src/test/scala/com/johnsnowlabs/nlp/annotators/cv/ViTImageClassificationTestSpec.scala>`__.
**Paper Abstract:**
*While the Transformer architecture has become the de-facto standard for natural
language processing tasks, its applications to computer vision remain limited. In
vision, attention is either applied in conjunction with convolutional networks, or
used to replace certain components of convolutional networks while keeping their
overall structure in place. We show that this reliance on CNNs is not necessary and
a pure transformer applied directly to sequences of image patches can perform very
well on image classification tasks. When pre-trained on large amounts of data and
transferred to multiple mid-sized or small image recognition benchmarks (ImageNet,
CIFAR-100, VTAB, etc.), Vision Transformer (ViT) attains excellent results compared
to state-of-the-art convolutional networks while requiring substantially fewer
computational resources to train.*
====================== ======================
Input Annotation types Output Annotation type
====================== ======================
``IMAGE`` ``CATEGORY``
====================== ======================
References
----------
`An Image is Worth 16x16 Words: Transformers for Image Recognition at Scale
<https://arxiv.org/abs/2010.11929>`__
Parameters
----------
doResize
Whether to resize the input to a certain size
doNormalize
Whether to normalize the input with mean and standard deviation
featureExtractorType
Name of model's architecture for feature extraction
imageMean
The sequence of means for each channel, to be used when normalizing images
imageStd
The sequence of standard deviations for each channel, to be used when normalizing images
resample
An optional resampling filter. This can be one of `PIL.Image.NEAREST`, `PIL.Image.BILINEAR` or
`PIL.Image.BICUBIC`. Only has an effect if do_resize is set to True.
size
Resize the input to the given size. If a tuple is provided, it should be (width, height). If only an integer is
provided, then the input will be resized to (size, size). Only has an effect if do_resize is set to True.
configProtoBytes
ConfigProto from tensorflow, serialized into byte array.
Examples
--------
>>> import sparknlp
>>> from sparknlp.base import *
>>> from sparknlp.annotator import *
>>> from pyspark.ml import Pipeline
>>> imageDF: DataFrame = spark.read \\
... .format("image") \\
... .option("dropInvalid", value = True) \\
... .load("src/test/resources/image/")
>>> imageAssembler = ImageAssembler() \\
... .setInputCol("image") \\
... .setOutputCol("image_assembler")
>>> imageClassifier = ViTForImageClassification \\
... .pretrained() \\
... .setInputCols(["image_assembler"]) \\
... .setOutputCol("class")
>>> pipeline = Pipeline().setStages([imageAssembler, imageClassifier])
>>> pipelineDF = pipeline.fit(imageDF).transform(imageDF)
>>> pipelineDF \\
... .selectExpr("reverse(split(image.origin, '/'))[0] as image_name", "class.result") \\
... .show(truncate=False)
+-----------------+----------------------------------------------------------+
|image_name |result |
+-----------------+----------------------------------------------------------+
|palace.JPEG |[palace] |
|egyptian_cat.jpeg|[Egyptian cat] |
|hippopotamus.JPEG|[hippopotamus, hippo, river horse, Hippopotamus amphibius]|
|hen.JPEG |[hen] |
|ostrich.JPEG |[ostrich, Struthio camelus] |
|junco.JPEG |[junco, snowbird] |
|bluetick.jpg |[bluetick] |
|chihuahua.jpg |[Chihuahua] |
|tractor.JPEG |[tractor] |
|ox.JPEG |[ox] |
+-----------------+----------------------------------------------------------+
"""
name = "ViTForImageClassification"
inputAnnotatorTypes = [AnnotatorType.IMAGE]
outputAnnotatorType = AnnotatorType.CATEGORY
configProtoBytes = Param(Params._dummy(),
"configProtoBytes",
"ConfigProto from tensorflow, serialized into byte array. Get with "
"config_proto.SerializeToString()",
TypeConverters.toListInt)
[docs] def getClasses(self):
"""
Returns labels used to train this model
"""
return self._call_java("getClasses")
[docs] def setConfigProtoBytes(self, b):
"""Sets configProto from tensorflow, serialized into byte array.
Parameters
----------
b : List[int]
ConfigProto from tensorflow, serialized into byte array
"""
return self._set(configProtoBytes=b)
@keyword_only
def __init__(self, classname="com.johnsnowlabs.nlp.annotators.cv.ViTForImageClassification",
java_model=None):
super(ViTForImageClassification, self).__init__(
classname=classname,
java_model=java_model
)
self._setDefault(
batchSize=2
)
@staticmethod
[docs] def loadSavedModel(folder, spark_session):
"""Loads a locally saved model.
Parameters
----------
folder : str
Folder of the saved model
spark_session : pyspark.sql.SparkSession
The current SparkSession
Returns
-------
ViTForImageClassification
The restored model
"""
from sparknlp.internal import _ViTForImageClassification
jModel = _ViTForImageClassification(folder, spark_session._jsparkSession)._java_obj
return ViTForImageClassification(java_model=jModel)
@staticmethod
[docs] def pretrained(name="image_classifier_vit_base_patch16_224", lang="en", remote_loc=None):
"""Downloads and loads a pretrained model.
Parameters
----------
name : str, optional
Name of the pretrained model, by default
"image_classifier_vit_base_patch16_224"
lang : str, optional
Language of the pretrained model, by default "en"
remote_loc : str, optional
Optional remote address of the resource, by default None. Will use
Spark NLPs repositories otherwise.
Returns
-------
ViTForImageClassification
The restored model
"""
from sparknlp.pretrained import ResourceDownloader
return ResourceDownloader.downloadModel(ViTForImageClassification, name, lang, remote_loc)


Jekyll is a static site generator used to design and develop static website that is simple, secure, flexible and powerful.
Static sites offer tons of advantages than dynamic websites. Static site generators such as Jekyll offers way more features than WordPress. Some of the cool advantages are
- Simple: There is no need of server-side programming. No backend. No server. Basic knowledge on front-end components such as HTML, CSS and JavaScript is enough to build a website.
- Security: As there is no server or database interaction involved, there is no possibility of attacks. In fact, you can see the entire code of your website rendered through Jekyll.
- Flexible: As you create your own website, you will have full control over it. Unlike Wordpress which has limited customization options, Jekyll offers full customization. You can add unlimited CSS classes or JavaScript files and even use a CSS preprocessor such as Sass which is highly helpful!
- Powerful: Your website will behave much faster as there is no server interaction involved.
- Hosting: After creating your Jekyll website, GitHub pages offer free hosting of Jekyll sites using GitHub. You just need a GitHub account and a repository to make your site live!
In this tutorial, we will create our first awesome website using Jekyll, host it in GitHub for free and get our free domain name similar to https://gogul09.github.io in 15 minutes.
Install Ruby in Windows
First, you need to install Ruby which is available here for Windows. Simply download the installer and complete the setup. After that, open up a command prompt and type gem -v. You should get something like this.
1 | 2.5.2 |
Also, you can type ruby -v and should get something like this to proceed.
1 | ruby 2.3.3p222 (2016-11-21 revision 56859) [i386-mingw32] |
Now, install bundler which provides a consistent environment for Ruby projects by tracking and installing the exact gems and versions that are needed.
1 | gem install bundler |
Install Github pages gem
After installing ruby, you need to install a gem called github-pages that includes all the dependencies and jekyll too.
1 | gem install github-pages |
Verify you have installed Jekyll by typing jekyll -v in the command prompt.
1 | jekyll 3.4.3 |
That’s it! You have installed all the dependencies to create your first awesome website.
Creating a new jekyll site
Before creating your first website, you need to follow a folder structure to keep everything organized. In case if you wish to create multiple sites, proper folder structure reduces so much stress in future while maintaining it. I follow the one below inside which all my websites are kept inside its own folder.
1 2 3 4 5 6 | g:\workspace\web g:\workspace\web (root-folder) -- first_awesome_website (sub-folder) -- second_cool_website (sub-folder) -- third_amazing_website (sub-folder) |
To create your first website, open up a command prompt, get into the above folder structure and type in the first Jekyll command jekyll new site_name. For this tutorial, I will keep the name of the website as first_awesome_website. You can keep any name as you like.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 | Running bundle install in g:/workspace/web/first_awesome_website... Bundler: Fetching gem metadata from https://rubygems.org/........... Bundler: Fetching version metadata from https://rubygems.org/.. Bundler: Fetching dependency metadata from https://rubygems.org/. Bundler: Resolving dependencies... Bundler: Installing public_suffix 3.0.2 Bundler: Using colorator 1.1.0 Bundler: Installing ffi 1.9.25 (x86-mingw32) Bundler: Using forwardable-extended 2.6.0 Bundler: Installing rb-fsevent 0.10.3 Bundler: Installing ruby_dep 1.5.0 Bundler: Installing kramdown 1.17.0 Bundler: Using liquid 3.0.6 Bundler: Using mercenary 0.3.6 Bundler: Using rouge 1.11.1 Bundler: Using safe_yaml 1.0.4 Bundler: Installing thread_safe 0.3.6 Bundler: Using bundler 1.14.0 Bundler: Installing addressable 2.5.2 Bundler: Installing rb-inotify 0.9.10 Bundler: Installing pathutil 0.16.1 Bundler: Installing tzinfo 1.2.5 Bundler: Installing sass-listen 4.0.0 Bundler: Installing listen 3.1.5 Bundler: Installing tzinfo-data 1.2018.5 Bundler: Installing sass 3.5.6 Bundler: Installing jekyll-watch 1.5.1 Bundler: Installing jekyll-sass-converter 1.5.2 Bundler: Using jekyll 3.4.3 Bundler: Installing jekyll-feed 0.10.0 Bundler: Using minima 2.1.1 Bundler: Bundle complete! 4 Gemfile dependencies, 26 gems now installed. Bundler: Use `bundle show [gemname]` to see where a bundled gem is installed. New jekyll site installed in g:/workspace/web/first_awesome_website. |
After executing the above command, Jekyll creates your website with default settings. You can go into the below path to check the contents that Jekyll has created.
1 2 3 4 5 6 | _posts _config.yml about.md Gemfile Gemfile.lock index.md |
We will look into all the above contents in a while. But before that, let’s see your website locally.
Get into the folder that we created first_awesome_website and execute the following two commands.
1 2 | jekyll build jekyll serve |
Above two commands should return results similar to the one shown below.
1 2 3 4 5 6 7 8 9 10 11 12 | WARN: Unresolved specs during Gem::Specification.reset: rb-fsevent (>= 0.9.4, ~> 0.9) rb-inotify (>= 0.9.7, ~> 0.9) WARN: Clearing out unresolved specs. Please report a bug if this causes problems. Configuration file: g:/workspace/web/first_awesome_website/_config.yml Source: g:/workspace/web/first_awesome_website Destination: g:/workspace/web/first_awesome_website/_site Incremental build: disabled. Enable with --incremental Generating... done in 0.588 seconds. Auto-regeneration: disabled. Use --watch to enable. |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 | WARN: Unresolved specs during Gem::Specification.reset: rb-fsevent (>= 0.9.4, ~> 0.9) rb-inotify (>= 0.9.7, ~> 0.9) WARN: Clearing out unresolved specs. Please report a bug if this causes problems. Configuration file: g:/workspace/web/first_awesome_website/_config.yml Configuration file: g:/workspace/web/first_awesome_website/_config.yml Source: g:/workspace/web/first_awesome_website Destination: g:/workspace/web/first_awesome_website/_site Incremental build: disabled. Enable with --incremental Generating... done in 0.378 seconds. Please add the following to your Gemfile to avoid polling for changes: gem 'wdm', '>= 0.1.0' if Gem.win_platform? Auto-regeneration: enabled for 'g:/workspace/web/first_awesome_website' Configuration file: g:/workspace/web/first_awesome_website/_config.yml Server address: http://<IP_ADDRESS>:4000/ Server running... press ctrl-c to stop. |
Now, you can visit our website locally at http://localhost:4000/. You should get something similar to the one shown below.
Awesome! You have made your own website using Jekyll in minutes. To quit the running procees, you can press CTRL + C in the command prompt. To view the site again locally, just type the command jekyll serve and view it in the browser at the same address http://localhost:4000/.
Keep in mind that you haven’t yet hosted your website. Hosting the website means you need a dedicated space in the internet for people to view your website if given a URL. GitHub Pages provides free web hosting for sites made from Jekyll. We will discuss it soon.
Running a jekyll site locally provides the following advantages.
- You can tweak/edit the site multiple times before making changes to the live website.
- You can use your favorite text editor to write your posts in Markdown and view the changes instantly in the browser locally.
- Only after making all the necessary changes, you can push it to GitHub and see it live.
Basic files & folders
Now, we will look into all the default files and folders created by Jekyll inside your master folder.
- _posts: This is the folder inside which all your blog posts will be kept. Whatever you write in this folder will be converted to html and corresponding styles will be applied automatically. All files must strictly follow the naming convention for proper parsing and display.
1 | yyyy-mm-dd-<post_name>.md |
- _site: This is the folder generated by Jekyll which will be used for distributing your website. All content inside this folder is what makes your site live. This folder gets updated automatically as you make changes. Do not update or delete or add anything inside this folder.
- config.yml: This is the YAML configuration file or shortly, the settings file for your site. It looks like the one shown below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 | # Welcome to Jekyll! # # This config file is meant for settings that affect your whole blog, values # which you are expected to set up once and rarely edit after that. If you find # yourself editing this file very often, consider using Jekyll's data files # feature for the data you need to update frequently. # # For technical reasons, this file is *NOT* reloaded automatically when you use # 'bundle exec jekyll serve'. If you change this file, please restart the server process. # Site settings # These are used to personalize your new site. If you look in the HTML files, # you will see them accessed via , , and so on. # You can create any custom variable you would like, and they will be accessible # in the templates via . title: Your awesome title email<EMAIL_ADDRESS>description: > # this means to ignore newlines until "baseurl:" Write an awesome description for your new site here. You can edit this line in _config.yml. It will appear in your document head meta (for Google search results) and in your feed.xml site description. baseurl: "" # the subpath of your site, e.g. /blog url: "" # the base hostname & protocol for your site, e.g. http://example.com twitter_username: jekyllrb github_username: jekyll # Build settings markdown: kramdown theme: minima gems: - jekyll-feed exclude: - Gemfile - Gemfile.lock |
This is basically a key-value file which is used to store important configurations for your website. Any changes made to this file requires terminating your local server process and restarting it. You can now modify the keys present in this file with your own values.
Hosting in GitHub Pages
Before jumping into the concepts of Jekyll, let’s first host your website in GitHub pages for free so that you will get your unique URL with which you can see your website live in the internet.
To host a Jekyll site in GitHub, you need a GitHub account. Make sure you follow that link to create a github account.
Now, you need to create a repository that acts as a container or master folder for your website. The name of your repository must be unique and this name is what you will be using to generate your unique GitHub URL. GitHub offers a free domain name for your website which comes like
1 | https://yourusername.github.io |
Follow this link to create a repository with the exact name as your GitHub account name with .github.io appended.
For example, my github account name is Gogul09 and so, I created a repository with the name Gogul09.github.io.
Execute the following git commands one by one to take your website to the GitHub repository that you created. Make sure you are still in the master folder first_awesome_website that you created in the command prompt at the beginning of this post and then execute these commands.
1 2 3 4 5 | git init git add . git commit -m "first commit" git remote add origin https://github.com/yourusername/yourrepo.git git push origin master -f |
After 5-10 minutes, you will be seeing your website using the below link.
1 | https://yourusername.github.io |
Congratulations! You have created your first website using Jekyll and hosted it for free using GitHub pages.
Powerful Sass Integration
If you don’t know the capabilities of a CSS preprocessor such as Sass, I highly encourage you to learn it. Using sass, you can make your CSS more structured, elegant and easier to modify.
When you develop websites, there comes a time when your single CSS file goes out of hands and its difficult to update a CSS class or modify a layout. In such situations, Sass is highly useful.
Jekyll has powerful integration for Sass. In fact, Jekyll comes with its own Sass compiler. Here are the steps to make use of Sass for your website.
- Create a folder named _sass in the root directory which is first_awesome_website for this tutorial.
- Create a file named style.scss in the root directory.
- Append the below lines in your _config.yml file.
1 2 | sass: style: compressed |
- First two lines of your style.scss should include triple dashes like the one shown below. After that you can use this file as the master Sass file for your website. You can also import Sass files residing inside _sass folder as shown below.
1 2 3 4 5 6 7 8 9 10 | --- --- @import "typography"; @import "colors"; // start writing after this div { width: 100%; } |
Note: Any file inside _sass folder must have _ appended to its name. For example, this is a Sass partial file - _typography.scss.
Customizing layout and style
The default theme provided by Jekyll is awesome and responsive. If you wish to override the default theme, carry on. For the rest of this tutorial, follow the below steps to modify the layout of your website and include custom styling.
- Create two folders in the root directory. _includes and _layouts.
- _includes folder will include all the pieces that comes repeatedly in your website such as header, footer, meta etc. We will create three files inside this folder for now.
- meta.html will hold all the meta tags inside head tag.
- header.html will hold all the header related elements such as logo, navigation bar etc.,
- footer.html will hold all the footer related elements such as copyrights etc.,
- _includes folder will include all the pieces that comes repeatedly in your website such as header, footer, meta etc. We will create three files inside this folder for now.
1 2 3 4 5 6 7 8 | <meta charset="utf-8"> <meta http-equiv="x-ua-compatible" content="ie=edge"> <meta name="viewport" content="width=device-width, initial-scale=1"> <title> "{% if page.title %}{{ page.title }}{% else %}{{ site.title }}{% endif %} </title> <link rel="stylesheet" type="text/css" href="/style.css" /> <link href='https://fonts.googleapis.com/css?family=Nunito' rel='stylesheet' type='text/css'> |
1 2 3 |
{{ site.name }}
  |
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Made with the awesome Jekyll
  |
Now, create a file named default.html inside _layouts directory. This will act as the blueprint for your website.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | <!DOCTYPE html>   {% include meta.html %}   {% include header.html %}

 {{ content }}

 {% include footer.html %}   |
Cool! Open up index.md and replace it with the following content.
1 2 3 4 5 6 7 8 9 10 11 12 13 | --- layout: default ---
Welcome to my Blog

 {% for post in site.posts %}

{{ post.title }}

 {% endfor %}
 |
Awesome! Open up style.scss and replace it with the following content.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 | --- --- body { background-color: #ffffff !important; margin: 0px; padding: 0px; font-family: "Nunito", sans-serif; } header { padding: 20px; background-color: rebeccapurple; text-align: center; h2 { color: white; font-weight: 100; } } footer { position: fixed; bottom: 0; right: 0; height: 60px; background-color: black; text-align: center; width: 100%; p { color: white; height: 60px; margin-top: 20px; font-size: 13px; } } .container { display: flex; margin-bottom: 100px; div { flex: 1; } article { flex: 1; } } article { background-color: #eaeaea; height: 100%; padding: 20px; h3 { text-align: center; } } .post-header { background-color: #252525 !important; border-radius: 10px; box-shadow: inset 0 3px 30px black; h1, p { color: white; font-weight: 100; } } |
Now, if you see your website locally http://localhost:4000, it will look like the one shown below.
Start exploring what we did above and your imagination is all that is needed to beautify layouts and styles.
References
In case if you found something useful to add to this article or you found a bug in the code or would like to improve some points mentioned, feel free to write it down in the comments. Hope you found something useful here.
Happy learning!