1D Flashcards
Modern wave generators produce outputs that are:
sinusoidal, square, rectangular, or sawtooth.
___ ___ are used extensively in the field of electronics and especially in the RF career field.
Wave generators
Wave generators are usually called ___.
oscillators
Oscillators are classified in two categories:
Sinusoidal and Non-sinusoidal
A ___ oscillator produces a sine wave output signal while ____ oscillators generate complex waveforms such as square waves, rectangular waves, trigger wave, and sawtooth waves.
sinusoidal
non-sinusoidal
A non-sinusoidal oscillator is often referred to as a ____ oscillator.
relaxation
An oscillator is a device that converts ___ from a power supply into an ___ signal.
DC
AC
The primary purpose of an oscillator is to generate a ___ ___ at a constant amplitude (peak-to-peak) and at a specific frequency while maintaining this waveform within certain limits.
repetitive waveform
Almost every piece of electronic equipment that uses an oscillator has two stability requirements:
amplitude (voltage) stability and frequency stability.
Amplitude stability refers to an oscillator’s ability to maintain a constant amplitude output waveform under normal circumstances. The more ____ the amplitude output waveform, the better the oscillator. Oscillators must have good amplitude stability to prevent voltage or current spikes that could damage equipment.
constant
Frequency stability refers to the oscillator’s ability to generate a signal at a ___ ___ with minimal frequency fluctuation.
constant frequency
The basic requirements to sustain oscillation at a constant amplitude and at a predetermined frequency are a:
DC Power Supply
Frequency Determining Device (FDD)
Amplifier
Regenerative Feedback
The following describes which of the four requirements for oscillation?
Oscillators operate at specific frequencies and require a ____ to create that frequency. ____ can be crystals, tank circuits (made up of inductors and capacitors), or RC (resistor and capacitor) networks. Another circuit, called a phase lock loop, is used in some modern oscillators to ensure frequency stability.
Frequency Determining Device (FDD)
Another circuit, called a ___ ___ ___, is used in some modern oscillators to ensure frequency stability.
phase lock loop
The following describes which of the four requirements for oscillation?
The ____ is necessary to provide voltage gain. The gain must be large enough to provide for the load device and supply a signal for regenerative feedback. The ____ uses a transistor, or other non-linear devices, to split the power requirement.
Amplifier
The following describes which of the four requirements for oscillation?
Returns the signal from the FDD to its proper amplitude. It provides the oscillator with amplitude stability and compensates for damping effects. Damping is the steady decrease in oscillation amplitude caused by internal resistance.
Regenerative Feedback
The following describes which of the four requirements for oscillation?
Provides the electrical power to the amplifier
DC Power Supply
Tank circuits are created by placing a capacitor and an inductor in ____.
parallel
A ___ ___, a type of crystal oscillator, is the most widely used oscillator.
quartz oscillator
The quartz crystal in the oscillator is a ___ ___ and must be excited and measured for proper operation.
mechanical resonator
Taking advantage of the ___ ___, which is the generation of a charge across the crystal or by mechanical compression, capitalizes on this phenomenon.
piezoelectric effect
When dealing with any crystal, ____ and ____ are two factors that influence its performance.
temperature and aging
Two solutions for the temperature issue are enclosing the crystal in an electronically regulated ___ or using a temperature-compensated crystal oscillator.
oven
Aging is the second factor affecting all quartz oscillators. These effects provide a near linear (uniform) change in resonant frequency
with time. We can’t ____ the deterioration of the oscillator as it ages, but good manufacturing designs can limit the deterioration, and we can observe and account for it.
prevent
As illustrated in Figure 1-147, crystals are mounted in holders which ____ support the crystals, ____ them from the elements, and provide the electrical ____. The holder must allow the crystal the freedom to vibrate.
physically
protect
connection
The crystal oscillator, shown in Figure 1-148 has an obvious identifying feature, being ___, the crystal.
Y1
The crystal (Y1) determines the oscillator’s output frequency, so it is the ___ of the oscillator.
FDD
___ ___ are used along with a crystal. The transistor, Q1, helps to guide the regenerative feedback back to the FDD in order to help maintain steady oscillation, while transistor Q2 is where the output waveform is generated.
Two transistors
Three of the four requirements of an oscillator are clearly seen in Figure1-148. ____, located at the top of the figure, is the power source, the ____ is the FDD, and the amplifier ___ provides
the output (a common base amplifier is used). The regenerative feedback, not clearly shown in Figure 1-148, consists of the output from Q2, from the tie point going left to the base of Q1. Q1 is a common collector amplifier that creates a lot of current through R1, which in turn creates a substantial voltage feeding back to crystal Y1 to keep Y1 energized and prevent the damping effect.
VCC
crystal
Q2
A good timing source is an oscillator that provides an ___ ___ when synchronizing a two- way communications network.
accurate clock
Accuracy is affected by several factors. One factor is the oscillator’s ____. A 10MHz oscillator is more accurate than a 5KHz oscillator because it breaks down each second of time into 10 million equal parts or cycles. The 5KHz oscillator breaks down each second into only 5,000 cycles. Another factor that can limit clock accuracy is an
increase in the amount of ____ in the output frequency.
frequency
drift
A timing oscillator is classified as either a ____ frequency standard or a ____ frequency standard.
primary
secondary
Any frequency source, regardless of its accuracy or stability, can be a primary frequency standard if it is used as the ___ ___ reference for other frequency sources.
sole calibration
A secondary frequency standard is a device that is calibrated
___ a primary frequency standard, and then used to calibrate other frequency sources.
against
For example, if you calibrate your watch to the clock in your work center, the work center clock becomes a ____ frequency standard, and your watch is a ____ frequency standard.
primary
secondary
Two kinds of oscillators commonly used as frequency sources are
____ oscillators and ____ oscillators.
quartz
atomic
___ ___ is considered the most accurate timing source because it generates more highly stable clocks than Mean Solar Time does.
Atomic Time
An atomic oscillator is used to create accurate seconds through the oscillations or vibrations of highly stable ___.
atoms
Two of the most common types of atomic oscillators are the
___ ___ ___ oscillator and the ___ ___ oscillator.
rubidium gas cell
cesium beam
Rubidium Gas only drifts approximately __ ___ in 24 hours.
1 microsecond
Cesium Beam drifts only ___ ___ in 24 hours.
200 nanoseconds
The ___ ___ ___ is an oscillator whose frequency can be varied using a
variable control voltage.
Voltage Control Oscillator (VCO)
As seen in Figure 1-149, ___ can produce several types of waveforms. This is a piece of test equipment used in the Air Force to test radio functions.
VCOs
The following schematic is a symbol for what?
Varactor
Figure 1-150 shows a VCO using a variable DC voltage. When the input voltage is increased, the output frequency is higher. Decreasing the input voltage will cause the opposite to happen. A tank circuit is used to store and transfer energy alternately between an inductor and a capacitor to produce a sinusoidal wave. The operation of this movement is called the ___ ___ since the signal rocks back and forth.
flywheel effect
In the VCO tank circuit, there is an additional component called a ___. A ___ (a variable diode) can be used as a voltage-variable capacitor to change the output frequency of the oscillator and allows it a greater frequency range for the output as well.
varactor
Voltage Controlled Oscillator uses components called ___ ___ and a ____.
tank circuits
varactor
As mentioned in the introduction, a VCO sometimes uses a circuit called a ___ ___ ___ (PLL) to create a more stable signal output.
Phase Lock Loop
In the previous section, we studied circuits that generated a sinusoidal wave. Now, we’ll discuss circuits that generate non-sinusoidal waves. These circuits, called ____, produce either a specific non-sinusoidal wave repeatedly, or they produce one non-sinusoidal wave when pulsed (triggered) while remaining inactive until another pulse is applied.
multivibrators
Circuits of this type are also referred to as relaxation oscillators.
Multivibrators
The output frequency of a multivibrator is a ____ wave or ____ wave.
square
rectangular
Multivibrators use the principle of an on-off switch. Multivibrators are basically two amplifier circuits, transistors, arranged with ___ ___. When an input voltage is large enough it will cause one transistor to act like an open switch and the other to act like a closed switch, producing a square or rectangular wave.
regenerative feedback
A square wave or rectangular wave can be produced by opening and closing the switch S1. This is essentially turning on and turning off the power, generating the highs (1) and lows (0) that create our wave form. If the switch is opened and closed for equal lengths of time, the output voltage will be a ____ wave (Figure 1-154). If the lengths of time are unequal, the output will be a ____ wave (Figure 1-155).
square
rectanglular
There are three basic types of multivibrators:
astable, bistable, and monostable
The following describes what type of waveform?
Two alternation equal in time
Voltage (amplitude) are also equal
Square Wave
The following describes what type of waveform?
Two alternation unequal in time
Voltage (amplitude) may not be equal
Rectangular Waveform
An ____ multivibrator has no stable states, causing its output to continuously oscillate between its two unstable states.
astable
The following describes which type of multivibrator?
No stable state
Free running (constantly switches) relaxation oscillator
Two outputs 180°
Astable
It is classified as a free-running multivibrator.
Astable
As the name ____ implies, this device has one stable state.
Monostable Multivibrator
It is a widely used multivibrator circuit that must always be triggered to generate each output pulse.
Monostable
The following describes which type of multivibrator?
Also referred to as start-stop or one-shot
One stable condition
Requires one trigger for each positive pulse
Output can be square wave or rectangular wave
Monostable
The following describes which type of multivibrator?
Also known as a Flip-Flop
Two stable states
Stays in last state until triggered to change
Requires 2 input triggers for each positive pulse
Bistable
Radar sets, oscilloscopes, and computer circuits all use ___ (voltage or current) waveforms. ___ waveshapes must have linear rise characteristics.
sawtooth
The sawtooth waveform is often used to produce a uniform, progressive movement of an electron beam across the face of the
oscilloscope screen. The movement of the electron beam is called a ____.
sweep
The circuit which provides the sawtooth waveform is called…?
sweep generator, time base generator, or ramp generator
Sawtooth waves can be generated by use of an ___ network in which the transistor operates as a switch.
RC
Output is used as external trigger sources for other circuits
Sawtooth generator
The linearity of the sawtooth is dependent on two variables: the time constant (TC) of the RC circuit and the length of the negative gate applied to the circuit. For the circuit to produce a linear
sawtooth, the components selected should be such that no more than one-tenth of one TC is used. Referring to the Universal Time Constant Chart in Figure 1-160, the most linear part of the curve
is the first __% of the first time constant.
10%
Oscillators require a ___, ___, ___ and ___ to sustain oscillations.
DC power source
amplifier
frequency-determining device (FDD)
regenerative feedback
Crystal Oscillators make use of a ____ as the frequency-determining device for good frequency stability.
crystal
A Voltage Control Oscillator varies frequency using a ____.
varactor
The lesson also covered multivibrators, which produce ___ ___.
non-sinusoidal waveforms
The astable multivibrator is a free-running device that can produce two square or rectangular waveform outputs ___° out of phase.
180 degrees
The monostable multivibrator has one steady state. It is also called a __-__ or __-__ multivibrator. It requires a trigger for each output pulse.
start-stop
one-shot
The bistable multivibrator (__-__) has two stable states and must be triggered to change states.
flip-flop
Sweep generators create a ___ waveform and are used for testing frequency response.
sawtooth
