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Amateur Extra License Class

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Title: Amateur Extra License Class


1
Amateur Extra License Class
  • Chapter 6
  • Electronic Circuits

2
Amplifiers
  • Any circuit that increases the strength of a
    signal voltage, current, or power.
  • Input voltages from microvolts to hundreds of
    volts.
  • Output powers from billionths of a watt to
    thousands of watts.

R
3
Amplifiers
  • Definitions.
  • Driver Circuit that supplies the input signal
    to the amplifier.
  • Load Circuit that receives the amplifiers
    output signal.
  • Final Amplifier Last amplifier stage in a
    transmitter.

R
4
Amplifiers
  • Amplifier Gain.
  • Ratio of output signal to input signal.
  • Voltage gain VOUT / VIN
  • Current gain IOUT / IIN
  • Power gain POUT / PIN
  • Can be expressed as simple ratio.
  • e.g. Voltage gain 10
  • Can be expressed in decibels.
  • e.g. Power gain 10 dB

R
5
Amplifiers
  • Input and Output Impedances.
  • Input impedance is load seen by driver.
  • Output Impedance is source impedance.
  • Maximum power transfer occurs when source load
    impedances are equal.

R
6
Amplifiers
  • Discrete Device Amplifiers
  • Common emitter.
  • Most common amplifier type.
  • Provides both voltage gain and current gain.
  • Input output voltages 180 out of phase.
  • Fairly high input impedance.
  • Output impedance depends on RL.

R
7
Amplifiers
  • Discrete Device Amplifiers
  • Common emitter.
  • R1 R2 provide fixed bias.
  • RE provides bias point stability.
  • a.k.a. Self-bias.
  • Prevents thermal runaway.
  • C2 allows maximum AC signal gain.
  • Emitter bypass.

R
8
Amplifiers
  • Discrete Device Amplifiers
  • Common base.
  • Provides voltage gain.
  • Current gain lt 1.
  • Input output
  • voltages in phase.
  • Low input impedance.
  • High output impedance.

R
9
Amplifiers
  • Discrete Device Amplifiers
  • Common collector.
  • a.k.a. - Emitter follower.
  • Provides current gain.
  • Voltage gain lt 1.
  • Input output voltages in phase.
  • Fairly high input impedance.
  • Low output impedance.
  • Linear voltage regulator.

R
10
Amplifiers
  • Vacuum Tube Amplifiers
  • Each type of transistor amplifier circuit has a
    corresponding vacuum tube amplifier circuit.
  • Common-Emitter ?? Common-Cathode.
  • Common-Base ?? Grounded-Grid.
  • Common-Collector ?? Common-Anode.
  • Emitter Follower ?? Cathode Follower.

R
11
Amplifiers
  • Vacuum Tube Amplifiers.
  • Grounded-Grid Amplifiers.
  • Most common RF power amplifier configuration.
  • Stable.
  • Easier to neutralize.
  • Low input impedance.
  • Little or no input impedance matching required.

R
12
Amplifiers
  • Op Amp Amplifiers
  • High-gain, direct-coupled, differential
    amplifier.
  • Differential input ? Input signal is difference
    between inverting non-inverting inputs.
  • Direct-coupled ? Will amplify DC.
  • Ideal operational amplifier
  • Infinite input impedance.
  • Zero output impedance.
  • Infinite gain.
  • Flat frequency response.
  • Zero offset voltage.
  • 0 VIN ? 0 VOUT

A
13
Amplifiers
A
14
Amplifiers
A
15
Amplifiers
  • Op Amp Amplifiers
  • Circuit characteristics totally determined by
    external components.
  • In closed-loop configuration
  • Input voltage 0.
  • Input current 0.

A
16
Amplifiers
  • Op Amp Amplifiers
  • Operational amplifier specifications.
  • Open-loop gain.
  • Gain-Bandwidth.
  • Slew rate.
  • Input offset voltage.
  • Input voltage in closed-loop.
  • Input impedance.
  • Output impedance.

A
17
Amplifiers
  • Op Amp Amplifiers
  • Practical operational amplifier.
  • Differential input.
  • Direct-coupled.
  • Very high input impedance.
  • Very low output impedance.
  • Very high voltage gain.
  • Up to 120 dB.
  • Wide bandwidth.

A
18
Amplifiers
LM741
A
19
Amplifiers
  • Op Amp Amplifiers
  • Inverting Amplifier.

Gain RF / RIN
A
20
Amplifiers
  • Operational Amplifiers (Op-Amps).
  • Non-inverting Amplifier.

Gain (RF R2) / R2
A
21
Amplifiers
  • Operational Amplifiers (Op-Amps).
  • Differential Amplifier.

Gain (R3 R1) / R1 or Gain (R4 R2) /
R2 where R1 R2 and R3 R4
A
22
Amplifiers
  • Operational Amplifiers (Op-Amps).
  • Summing Amplifier.
  • Vout - ((V1 x RF /Rin) (V2 x RF /Rin) (V3
    x RF /Rin))
  • Vout - (V1 V2 V3) x RF /Rin

A
23
Amplifiers
  • Amplifier Classes.
  • Class A
  • On for 360
  • Best linearity.
  • Least efficient.
  • Class B
  • On for 180
  • Non-linear.
  • 2 devices in push-pull configuration is linear.
  • More efficient.

A
24
Amplifiers
  • Amplifier Classes.
  • Class AB
  • On for gt180 but lt 360
  • Non-linear.
  • 2 devices in push-pull configuration is linear.
  • Compromise between classes A B
  • Class C
  • On for lt180
  • Highly non-linear.
  • Most efficient.

A
25
Amplifiers
  • Amplifier Classes.
  • Class D
  • Used for audio amplifiers.
  • Uses switching techniques to achieve high
    efficiency.
  • Switching speed well above highest frequency to
    be amplified.
  • Efficiency gt90.

A
26
Amplifiers
  • Distortion and Intermodulation.
  • Distortion
  • Non-linearity results in distortion.
  • ALL physical components have some non-linearity.
  • Distortion results in harmonics.
  • Can have low distortion or high efficiency, but
    not both.

A
27
Amplifiers
  • Distortion and Intermodulation.
  • Intermodulation.
  • 2 or more signals mixing together to produce
    other frequencies.
  • FIMD (A x F1) (B x F2).
  • If AB is odd, then odd-order intermodulation
    product.
  • Fimd is near fundamental or odd harmonics of F1
    F2.
  • If AB is even then even-order intermodulation
    product.
  • Fimd is near even harmonics of F1 F2.
  • Since odd-order IMD products are close to desired
    frequency, spurious signals can be transmitted.

A
28
Amplifiers
  • Distortion and Intermodulation.
  • Tuned amplifiers.
  • Power amplifiers are a compromise between
    linearity efficiency.
  • Tuned output circuit acts like a flywheel,
    minimizing effects of distortion.

A
29
Amplifiers
  • Distortion and Intermodulation.
  • Selecting amplifier class.
  • For audio, AM or SSB, a linear amplifier is
    required.
  • For CW or FM, a non-linear amplifier may be used.

A
30
Amplifiers
  • Distortion and Intermodulation.
  • Selecting amplifier class.
  • For best linearity lowest efficiency, use Class
    A.
  • Low-level stages.
  • Audio power amplifiers.
  • For a good compromise between linearity
    efficiency, use Class AB.
  • RF Power amplifiers.

A
31
Amplifiers
  • Distortion and Intermodulation.
  • Selecting amplifier class.
  • For highest efficiency or intentional harmonics,
    use Class C.
  • Frequency multiplier stages.
  • CW transmitters.
  • FM transmitters receivers.

A
32
Amplifiers
  • Distortion and Intermodulation.
  • Selecting amplifier class.
  • Class B push-pull circuits.
  • Audio power amplifiers.
  • Even harmonics are reduced.

A
33
Amplifiers
  • Instability and Parasitic Oscillation.
  • Amplifier stability.
  • Excessive gain or undesired positive feedback can
    cause an amplifier to oscillate.
  • Can occur in any amplifier stage, not just power
    amplifiers.
  • Can result in
  • Increased noise figure in receiver.
  • Spurious radiations.
  • Excessive heating.

R
34
Amplifiers
  • Instability and Parasitic Oscillation.
  • Neutralization.
  • Inter-electrode capacitances in amplifying device
    and/or stray capacitances in associated circuitry
    can cause an amplifier to oscillate at the
    frequency of operation.
  • Oscillation can be prevented by neutralizing the
    amplifier.
  • Feed small amount of signal back to input
    out-of-phase.

R
35
Amplifiers
  • Instability and Parasitic Oscillation.
  • Neutralization.

R
36
Amplifiers
  • Instability and Parasitic Oscillation.
  • Parasitic oscillation.
  • Not related to operating frequency.
  • Caused by resonances in surrounding circuitry.
  • Typically at VHF or UHF frequencies.
  • Parasitic oscillations in HF vacuum tube
    amplifiers are eliminated by adding parasitic
    suppressors to the plate or grid leads.
  • Coil in parallel with resistor.

R
37
Amplifiers
  • Instability and Parasitic Oscillation.
  • Parasitic suppressor.

R
38
Amplifiers
  • Instability and Parasitic Oscillation.
  • Parasitic suppressor.

R
39
Amplifiers
  • VHF, UHF, and Microwave Amplifiers.
  • At VHF higher frequencies, special techniques
    devices are required to design construct
    amplifiers.
  • Short wavelengths mean component leads can have
    significant inductance.
  • Due to internal capacitances, ordinary tubes
    transistors lose ability to amplify.
  • The following slides describe only some of the
    devices techniques used.

R
40
Amplifiers
  • VHF, UHF, and Microwave Amplifiers.
  • Klystrons.
  • Velocity modulation.

R
41
Amplifiers
  • VHF, UHF, and Microwave Amplifiers.
  • Parametric amplifiers.
  • Invented by amateur radio operators.
  • Uses variable reactance (varactor diode) to
    pump input signal.
  • Used for very low noise receive pre-amplifiers at
    microwave frequencies above.

R
42
Amplifiers
  • VHF, UHF, and Microwave Amplifiers.
  • Parametric amplifiers.

R
43
Amplifiers
  • VHF, UHF, and Microwave Amplifiers.
  • Microwave semiconductor amplifiers.
  • Geometry of junction transistors limits upper
    frequency limit to a few GHz.
  • Gallium-Arsenide FETs can operate up to 20-30
    GHz.

R
44
  • E7B12 -- What type of circuit is shown in Figure
    E7-1?
  1. Switching voltage regulator
  2. Linear voltage regulator
  3. Common emitter amplifier
  4. Emitter follower amplifier

45
  • E7B10 -- In Figure E7-1, what is the purpose of
    R1 and R2?
  1. Load resistors
  2. Fixed bias
  3. Self bias
  4. Feedback

46
  • E7B11 -- In Figure E7-1, what is the purpose of
    R3?
  1. Fixed bias
  2. Emitter bypass
  3. Output load resistor
  4. Self bias

47
  • E7B15 -- What is one way to prevent thermal
    runaway in a bipolar transistor amplifier?
  1. Neutralization
  2. Select transistors with high beta
  3. Use a resistor in series with the emitter
  4. All of these choices are correct

48
  • E7B13 -- In Figure E7-2, what is the purpose of R?
  1. Emitter load
  2. Fixed bias
  3. Collector load
  4. Voltage regulation

49
  • E7B18 What is a characteristic of a
    grounded-grid amplifier?
  1. High power gain
  2. High filament voltage
  3. Low input impedance
  4. Low bandwidth

50
  • E7G12 -- What is an integrated circuit
    operational amplifier?
  1. A high-gain, direct-coupled differential
    amplifier with very high input and very low
    output impedance
  2. A digital audio amplifier whose characteristics
    are determined by components external to the
    amplifier
  3. An amplifier used to increase the average output
    of frequency modulated amateur signals to the
    legal limit
  4. An RF amplifier used in the UHF and microwave
    regions

51
  • E7G01 What is the typical output impedance of
    an integrated circuit op-amp?
  1. Very low
  2. Very high
  3. 100 ohms
  4. 1000 ohms

52
  • E7G03 What is typical input impedance of an
    integrated circuit op-amp?
  1. 100 ohms
  2. 1000 ohms
  3. Very low
  4. Very high

53
  • E7G08 -- How does the gain of an ideal
    operational amplifier vary with frequency?
  1. It increases linearly with increasing frequency
  2. It decreases linearly with increasing frequency
  3. It decreases logarithmically with increasing
    frequency
  4. It does not vary with frequency

54
  • E7G04 What is meant by the term op-amp input
    offset voltage?
  1. The output voltage of the op-amp minus its input
    voltage
  2. The difference between the output voltage of the
    op-amp and the input voltage required in the
    immediately following stages
  3. The differential input voltage needed to bring
    the open loop output voltage to zero
  4. The potential between the amplifier input
    terminal of the op-amp in an open loop condition

55
  • E7G10 -- What absolute voltage gain can be
    expected from the circuit in Figure E7-4 when R1
    is 1800 ohms and RF is 68 kilohms?
  1. 1
  2. 0.03
  3. 38
  4. 76

56
  • E7G07 -- What magnitude of voltage gain can be
    expected from the circuit in Figure E7-4 when R1
    is 10 ohms and RF is 470 ohms?
  1. 0.21
  2. 94
  3. 47
  4. 24

57
  • E7G11 -- What absolute voltage gain can be
    expected from the circuit in Figure E7-4 when R1
    is 3300 ohms and RF is 47 kilohms?
  1. 28
  2. 14
  3. 7
  4. 0.07

58
  • E7G09 -- What will be the output voltage of the
    circuit shown in Figure E7-4 if R1 is 1000 ohms,
    RF is 10,000 ohms, and 0.23 volts dc is applied
    to the input?
  1. 0.23 volts
  2. 2.3 volts
  3. -0.23 volts
  4. -2.3 volts

59
  • E6C02 What happens when the level of a
    comparators input signal crosses the threshold?
  1. The IC input can be damaged
  2. The comparator changes its output state
  3. The comparator enters latch-up
  4. The feedback loop becomes unstable

60
  • E6C01 What is the function of hysteresis in a
    comparator?
  1. To prevent input noise from causing unstable
    output signals
  2. To allow the comparator to be used with AC input
    signals
  3. To cause the output to change states continually
  4. To increase the sensistivity

61
  • E7B04 -- Where on the load line of a Class A
    common emitter amplifier would bias normally be
    set?
  1. Approximately half-way between saturation and
    cutoff
  2. Where the load line intersects the voltage axis
  3. At a point where the bias resistor equals the
    load resistor
  4. At a point where the load line intersects the
    zero bias current curve

62
  • E7B06 -- Which of the following amplifier types
    reduces or eliminates even-order harmonics?
  1. Push-push
  2. Push-pull
  3. Class C
  4. Class AB

63
  • E7B01 -- For what portion of a signal cycle does
    a Class AB amplifier operate?
  1. More than 180 degrees but less than 360 degrees
  2. Exactly 180 degrees
  3. The entire cycle
  4. Less than 180 degrees

64
  • E7B07 -- Which of the following is a likely
    result when a Class C amplifier is used to
    amplify a single-sideband phone signal?
  1. Reduced intermodulation products
  2. Increased overall intelligibility
  3. Signal inversion
  4. Signal distortion and excessive bandwidth

65
  • E7B14 Why are switching amplifiers more
    efficient than linear amplifiers?
  1. Switching amplifiers operate at higher voltages
  2. The power transistor is at saturation or cut off
    most of the time, resulting in low power
    dissipation
  3. Linear amplifiers have high gain resulting in
    higher harmonic content
  4. Switching amplifiers use push-pull circuits

66
  • E7B02 -- What is a Class D amplifier?
  1. A type of amplifier that uses switching
    technology to achieve high efficiency
  2. A low power amplifier using a differential
    amplifier for improved linearity
  3. An amplifier using drift-mode FETs for high
    efficiency
  4. A frequency doubling amplifier

67
  • E7B03 -- Which of the following forms the output
    of a class D amplifier circuit?
  1. A low-pass filter to remove switching signal
    components
  2. A high-pass filter to compensate for low gain at
    low frequencies
  3. A matched load resistor to prevent damage by
    switching transients
  4. A temperature-compensated load resistor to
    improve linearity

68
  • E7B16 -- What is the effect of intermodulation
    products in a linear power amplifier?
  1. Transmission of spurious signals
  2. Creation of parasitic oscillations
  3. Low efficiency
  4. All of these choices are correct

69
  • E7B17 -- Why are odd-order rather than even-order
    intermodulation distortion products of particular
    concern in linear power amplifiers?
  1. Because they are relatively close in frequency to
    the desired signal
  2. Because they are relatively far in frequency from
    the desired signal
  3. Because they invert the sidebands causing
    distortion
  4. Because they maintain the sidebands, thus causing
    multiple duplicate signals

70
  • E7B05 -- What can be done to prevent unwanted
    oscillations in an RF power amplifier?
  1. Tune the stage for maximum SWR
  2. Tune both the input and output for maximum power
  3. Install parasitic suppressors and/or neutralize
    the stage
  4. Use a phase inverter in the output filter

71
  • E7B08 -- How can an RF power amplifier be
    neutralized?
  1. By increasing the driving power
  2. By reducing the driving power
  3. By feeding a 180-degree out-of-phase portion of
    the output back to the input
  4. By feeding an in-phase component of the output
    back to the input

72
Break
73
Signal Processing
  • Oscillator Circuits Characteristics.
  • Generates sine wave.
  • Amplifier with positive feedback.
  • AV Amplifier gain.
  • ß Feedback ratio.
  • Loop Gain AV x ß
  • If loop gain gt 1 and in phase, circuit will
    oscillate.

A
74
Signal Processing
  • Oscillator Circuits Characteristics.
  • Colpitts oscillator.
  • Tapped capacitance.
  • Hartley oscillator.
  • Tapped inductance.

A
75
Signal Processing
  • Oscillator Circuits Characteristics.
  • Pierce oscillator.
  • Tuned circuit replaced
  • with a crystal.

A
76
Signal Processing
  • Oscillator Circuits Characteristics.
  • Crystals.
  • Usually small wafer of quartz with precise
    dimensions.
  • Piezoelectric effect.
  • Crystal deforms mechanically when voltage
    applied.
  • Voltage generated when crystal deformed.

A
77
Signal Processing
  • Oscillator Circuits Characteristics.
  • Crystals.
  • Equivalent circuit.
  • C1 Motional capacitance
  • L1 Motional inductance
  • R1 Loss resistance
  • C0 Electrode stray capacitance

A
78
Signal Processing
  • Oscillator Circuits Characteristics.
  • Crystals.
  • Frequency is accurate when connected to a
    specified parallel capacitance.

A
79
Signal Processing
  • Oscillator Circuits Characteristics.
  • Variable-frequency oscillator.
  • Make either L or C adjustable.
  • Not as stable.

A
80
Signal Processing
  • Oscillator Circuits Characteristics.
  • Microwave oscillators.
  • Magnetron.
  • Diode tube with a resonant cavity surrounded by
    external magnet.
  • Magnetic field causes electrons to spiral,
    generating RF energy at a frequency determined by
    the dimensions of the cavity.

A
81
Signal Processing
  • Oscillator Circuits Characteristics.
  • Microwave oscillators.
  • Gunn diode oscillators.
  • Diode.
  • Similar to tunnel diode.
  • Negative resistance.
  • Resonant cavity

A
82
Signal Processing
  • Digital Signal Processing (DSP)
  • Part of practically all modern transceivers.
  • Allows signal processing difficult to obtain by
    analog methods.
  • Procedure
  • Convert analog signal to series of numbers.
  • Process series of numbers mathematically.
  • Convert resulting series of numbers back to
    analog signal.

R
83
Signal Processing
  • Digital Signal Processing (DSP)
  • Analog-to-digital conversion.
  • Sequential sampling.
  • Sample signal at regular intervals (sequential
    sampling).
  • Convert signal value to a number.
  • Higher sampling rates yields higher accuracy.
  • More bits in the number yields higher accuracy

R
84
Signal Processing
  • Digital Signal Processing (DSP)
  • Sine wave, alias sine wave, harmonic sampling.
  • If sample rate is less than frequency of signal
    being sampled, result does not match input
    signal.
  • Retains general shape of sine wave but at lower
    frequency.
  • Downward frequency translation can be useful.
  • Longer time between samples provides more
    processing time.

R
85
Signal Processing
  • Digital Signal Processing (DSP)
  • Sine wave, alias sine wave, harmonic sampling.
  • Harmonic sampling.
  • If frequency of signal being sampled is about
    twice the sampling rate, result is exactly same
    as if frequency is equal to sampling rate.
  • Must limit bandwidth of signal being sampled.

R
86
Signal Processing
  • Digital Signal Processing (DSP)
  • Sine wave, alias sine wave, harmonic sampling.
  • Aliasing.
  • Nyquist sampling theorem.
  • To avoid aliasing, sampling rate must be 2x
    highest frequency being sampled.

R
87
Signal Processing
  • Digital Signal Processing (DSP)
  • Data converters.
  • Analog-to-digital converter (ADC).
  • Device that performs analog-to-digital
    conversion.
  • Produces a binary number that is directly
    proportional to value of the input voltage.
  • More bits in binary number ? higher resolution.
  • 8 bits ? 256 steps.
  • 16 bits ? 65,536 steps.
  • 24 bits ? 16,777,216 steps.

R
88
Signal Processing
  • Digital Signal Processing (DSP)
  • Data converters.
  • Digital-to-analog converter (DAC).
  • Device that performs digital-to-analog
    conversion.
  • Produces an output voltage that is directly
    proportional to value of a binary number.
  • More bits in binary number ? higher resolution.
  • 8 bits ? 256 steps.
  • 16 bits ? 65,536 steps.
  • 24 bits ? 16,777,216 steps.

R
89
Signal Processing
  • Digital Signal Processing (DSP)
  • Representation of Numbers.
  • Floating Point
  • Similar to scientific notation.
  • Greater range of numbers can be handled.
  • Not necessary for DSP since range of numbers
    limited by precision of ADC.
  • Used in PCs.
  • Fixed Point
  • Fraction lt1.
  • Used for most DSP in amateur equipment.

R
90
Signal Processing
  • Digital Signal Processing (DSP)
  • Software-Defined Radio (SDR).
  • A software-defined radio (SDR) system is a radio
    communication system where components that have
    been typically implemented in hardware (e.g.
    mixers, filters, modulators/demodulators,
    detectors, etc.) are instead implemented by means
    of software on a computer or embedded computing
    devices.

R
91
Signal Processing
  • Digital Signal Processing (DSP)
  • Software-Defined Radio (SDR).
  • The ideal SDR receiver would be to attach an
    antenna to an analog-to-digital converter (ADC).
  • Similarly, the ideal SDR transmitter would be to
    attach a digital-to-analog converter (DAC) to an
    antenna.
  • Not feasible with current technology, so some
    compromise is necessary.

R
92
Signal Processing
  • Digital Signal Processing (DSP)
  • Software-Defined Radio (SDR).
  • Some analog processing still required.
  • Future is an all-digital radio.
  • Commercial SDRs now available for amateur use.

R
93
Signal Processing
  • Mixers
  • Used to change the frequency of a signal.
  • Mathematically combine 2 frequencies together,
    generating 4 output frequencies.
  • f1 f2 ? f1, f2, f1f2, f1f2
  • Superheterodyne receiver.
  • fRF fLO ? frf flo

R
94
Signal Processing
  • Mixers
  • Only enough pre-amp gain should be used to
    overcome mixer losses.
  • Excessive input signal can
  • Overload mixer circuit.
  • Distort signal.
  • Generate spurious mixer products.
  • Operation of a mixer is similar to operation of
    product detectors modulators.

R
95
Signal Processing
  • Mixers

R
96
Signal Processing
  • Mixers
  • Passive mixers.
  • Uses passive components such as diodes.
  • No amplification.
  • Some conversion loss.
  • Require strong LO signal.
  • Generate noise.

R
97
Signal Processing
  • Mixers
  • Single-balanced mixer.

R
98
Signal Processing
  • Mixers
  • Double-balanced mixer.
  • fRF fLO are suppressed leaving only sum
    difference frequencies.

R
99
Signal Processing
  • Mixers
  • Active mixers.
  • Uses active components such as transistors or
    FETs.
  • Amplification possible.
  • No conversion loss.
  • Less LO signal needed.
  • Generate less noise.
  • Strong signal handling capability not as good as
    passive mixers.

R
100
Signal Processing
  • Mixers
  • Dual-gate MOSFET mixer.

R
101
Signal Processing
  • Modulation
  • Combining a modulating signal with an RF signal
    resulting in a signal that can be transmitted.
  • Modulating signal also known as the baseband
    signal.

R
102
Signal Processing
  • Modulators
  • Amplitude modulation.
  • Multiplying (mixing) AF signal carrier produces
    amplitude modulated signal.

R
103
Signal Processing
  • Modulators
  • Single-sideband modulation.
  • Filter method.
  • Start with AM double-sideband signal use
    filters to remove one sideband the carrier.
  • Better idea use a balanced modulator (mixer) to
    generate a double-sideband suppressed carrier
    signal. Then all you have to filter out is the
    unwanted sideband.

R
104
Signal Processing
  • Modulators
  • Single-sideband modulation.
  • Phasing (quadrature) method.
  • Generate 2 identical carrier signals, 90 out of
    phase.
  • Generate 2 identical audio signals, 90 out of
    phase.
  • Mix these together in a pair of balanced
    modulators result is that the carrier one
    sideband are canceled out leaving only one
    sideband.
  • 90 phase shift of band of audio frequencies
    difficult to accomplish in hardware, but easy in
    software.
  • Hilbert-transform filters.
  • Most SDR transmitters use the phasing or
    quadrature method to generate SSB mathematically.

R
105
Signal Processing
  • Modulators
  • Single-sideband modulation.
  • Phasing (quadrature) method.

R
106
Signal Processing
  • Modulators
  • Frequency and phase modulation.
  • Direct FM
  • Frequency deviation constant with
  • modulating frequency.
  • Generated by adding reactance
  • modulator to oscillator circuit.

A
107
Signal Processing
  • Modulators
  • Frequency and phase modulation.
  • Indirect FM (phase modulation).
  • Frequency deviation increases with increasing
    modulating frequency.
  • Generated by adding reactance modulator to any
    stage other than the oscillator.

A
108
Signal Processing
  • Modulators
  • Frequency and phase modulation.
  • Pre-emphasis is amplifying the higher modulating
    frequencies more than the lower frequencies.
  • Adding pre-emphasis to the modulating signal of
    an FM transmitter yields a PM signal.
  • Pre-emphasis yields a better signal-to-noise
    ratio.
  • Corresponding de-emphasis is added to the
    receiver.

A
109
Signal Processing
  • Detectors and Demodulators
  • Detectors.
  • Simplest detector is the diode detector.
  • a.k.a. Envelope detector.

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110
Signal Processing
  • Detectors and Demodulators
  • Product Detectors.
  • Mixes signal with a local oscillator to retrieve
    the modulating signal.
  • fRF x fLO ? fRFfLO ? fAF

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111
Signal Processing
  • Detectors and Demodulators
  • Product Detectors.
  • For AM, local oscillator frequency phase must
    precisely match AM signal carrier.
  • For SSB, local oscillator frequency must match
    carrier frequency of suppressed carrier.
  • For CW, local oscillator frequency is offset from
    signal frequency to produce a sidetone.

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112
Signal Processing
  • Detectors and Demodulators
  • Direct Conversion.
  • Local oscillator is at the frequency of the
    received signal.
  • Requires very stable local oscillator.
  • Software-defined radios (SDR) typically uses a
    modified direct-conversion technique.
  • Signal is converted to a baseband AF signal for
    A-to-D conversion processing.

R
113
Signal Processing
  • Detectors and Demodulators
  • Detecting FM signals.
  • Frequency discriminator.
  • a.k.a. Foster-Seeley Detector.

R
114
Signal Processing
  • Detectors and Demodulators
  • Detecting FM signals.
  • Ratio detector.

R
115
Signal Processing
  • Detectors and Demodulators
  • Detecting FM signals.
  • Slope detector.
  • Use AM receivers selectivity curve to detect FM.

R
116
Signal Processing
  • Frequency Synthesis
  • Phase-Locked Loop (PLL).

A
117
Signal Processing
  • Frequency Synthesis
  • Phase-Locked Loop (PLL).
  • Servo loop
  • Error-detecting circuit with negative feedback.
  • Allows VFO to have stability of crystal
    oscillator.
  • Can do FM modulation demodulation.
  • Capture range Range of frequencies over which
    PLL can achieve lock.
  • Spectral impurities are mainly broadband phase
    noise.
  • PLL has been replaced in modern designs by direct
    digital synthesis.

A
118
Signal Processing
  • Frequency Synthesis
  • Direct Digital Synthesis (DDS).
  • Generates sine wave by looking up values in a
    table.
  • Changing phase increment changes frequency.
  • Increase tuning range by adding PLL.
  • No phase noise, but spurs at discrete
    frequencies.

A
119
  • E7H04 -- How is positive feedback supplied in a
    Colpitts oscillator?
  1. Through a tapped coil
  2. Through link coupling
  3. Through a capacitive divider
  4. Through a neutralizing capacitor

120
  • E7H03 -- How is positive feedback supplied in a
    Hartley oscillator?
  1. Through a tapped coil
  2. Through a capacitive divider
  3. Through link coupling
  4. Through a neutralizing capacitor

121
  • E7H01 -- What are three oscillator circuits used
    in Amateur Radio equipment?
  1. Taft, Pierce and negative feedback
  2. Pierce, Fenner and Beane
  3. Taft, Hartley and Pierce
  4. Colpitts, Hartley and Pierce

122
  • E7H05 -- How is positive feedback supplied in a
    Pierce oscillator?
  1. Through a tapped coil
  2. Through link coupling
  3. Through a neutralizing capacitor
  4. Through a quartz crystal

123
  • E7H13 Which of the following is a technique for
    providing highly accurate and stable oscillators
    needed for microwave transmission and reception?
  1. Use a GPS signal reference
  2. Use a rubidium stabilized reference oscillator
  3. Use a temperature controlled high Q dielectric
    resonator
  4. All of these choices are correct

124
  • E7H06 -- Which of the following oscillator
    circuits are commonly used in VFOs?
  1. Pierce and Zener
  2. Colpitts and Hartley
  3. Armstrong and deForest
  4. Negative feedback and balanced feedback

125
  • E6D03 Which of the following is an aspect of
    the piezoelectric effect?
  1. Mechanical deformation of material by the
    application of a voltage
  2. Mechanical deformation of material by a magnetic
    field
  3. Generation of electrical energy in the presence
    of light
  4. Increased conductivity in the presence of light

126
  • E6D02 What is the equivalent circuit of a
    crystal quartz?
  1. Motional capacitance, motional inductance, and
    loss resistance in series, all in parallel with a
    shunt capacitor representing electrode and stray
    capacitance.
  2. Motional capacitance, motional inductance, loss
    resistance and a capacitor representing electrode
    and stray capacitance all in parallel.
  3. Motional capacitance, motional inductance, loss
    resistance and a capacitor representing electrode
    and stray capacitance all in series.
  4. Motional inductance and loss resistance in
    series, paralleled with motional capacitance and
    a capacitor representing electrode and stray
    capacitance.

127
  • E7H12 -- Which of the following must be done to
    ensure that a crystal oscillator provides the
    frequency specified by the crystal manufacturer?
  1. Provide the crystal with a specified parallel
    inductance
  2. Provide the crystal with a specified parallel
    capacitance
  3. Bias the crystal at a specified voltage
  4. Bias the crystal at a specified current

128
  • E7H02 -- What describes a microphonic?
  1. An IC used for amplifying microphone signals
  2. Distortion caused by RF pickup on the microphone
    cable
  3. Changes in the oscillator frequency due to
    mechanical vibration
  4. Excess loading of the microphone by an oscillator

129
  • E7H07 How can an oscillators microphonic
    responses be reduced?
  1. Use of NP0 capacitors
  2. Eliminating noise on the oscillators power
    supply
  3. Using the oscillator only for CW and digital
    signals
  4. Mechanically isolating the oscillator circuitry
    from its enclosure

130
  • E7H08 Which of the following components can be
    used to reduce thermal drift in crystal
    oscillators?
  1. Use of NP0 capacitors
  2. Toroidal inductors
  3. Wirewound resistors
  4. Non-inductive resistors

131
  • E7H09 -- What type of frequency synthesizer
    circuit uses a phase accumulator, lookup table,
    digital to analog converter and a low-pass
    anti-alias filter?
  1. A direct digital synthesizer
  2. A hybrid synthesizer
  3. A phase locked loop synthesizer
  4. A diode-switching matrix synthesizer

132
  • E7H10 -- What information is contained in the
    lookup table of a direct digital frequency
    synthesizer?
  1. The phase relationship between a reference
    oscillator and the output waveform
  2. The amplitude values that represent a sine-wave
    output
  3. The phase relationship between a
    voltage-controlled oscillator and the output
    waveform
  4. The synthesizer frequency limits and frequency
    values stored in the radio memories

133
  • E7H11 -- What are the major spectral impurity
    components of direct digital synthesizers?
  1. Broadband noise
  2. Digital conversion noise
  3. Spurious signals at discrete frequencies
  4. Nyquist limit noise

134
  • E7H14 -- What is a phase-locked loop circuit?
  1. An electronic servo loop consisting of a ratio
    detector, reactance modulator, and
    voltage-controlled oscillator
  2. An electronic circuit also known as a monostable
    multivibrator
  3. An electronic servo loop consisting of a phase
    detector, a low-pass filter, a voltage-controlled
    oscillator, and a stable reference oscillator
  4. An electronic circuit consisting of a precision
    push-pull amplifier with a differential input

135
  • E7H15 -- Which of these functions can be
    performed by a phase-locked loop?
  1. Wide-band AF and RF power amplification
  2. Comparison of two digital input signals, digital
    pulse counter
  3. Photovoltaic conversion, optical coupling
  4. Frequency synthesis, FM demodulation

136
  • E7E08 -- What are the principal frequencies that
    appear at the output of a mixer circuit?
  1. Two and four times the original frequency
  2. The sum, difference and square root of the input
    frequencies
  3. The two input frequencies along with their sum
    and difference frequencies
  4. 1.414 and 0.707 times the input frequency

137
  • E7E09 -- What occurs when an excessive amount of
    signal energy reaches a mixer circuit?
  1. Spurious mixer products are generated
  2. Mixer blanking occurs
  3. Automatic limiting occurs
  4. A beat frequency is generated

138
  • E7E07 -- What is meant by the term baseband in
    radio communications?
  1. The lowest frequency band that the transmitter or
    receiver covers
  2. The frequency components present in the
    modulating signal
  3. The unmodulated bandwidth of the transmitted
    signal
  4. The basic oscillator frequency in an FM
    transmitter that is multiplied to increase the
    deviation and carrier frequency

139
  • E7E01 -- Which of the following can be used to
    generate FM phone emissions?
  1. A balanced modulator on the audio amplifier
  2. A reactance modulator on the oscillator
  3. A reactance modulator on the final amplifier
  4. A balanced modulator on the oscillator

140
  • E7E02 -- What is the function of a reactance
    modulator?
  1. To produce PM signals by using an electrically
    variable resistance
  2. To produce AM signals by using an electrically
    variable inductance or capacitance
  3. To produce AM signals by using an electrically
    variable resistance
  4. To produce PM signals by using an electrically
    variable inductance or capacitance

141
  • E7E03 -- How does an analog phase modulator
    function?
  1. By varying the tuning of a microphone
    preamplifier to produce PM signals
  2. By varying the tuning of an amplifier tank
    circuit to produce AM signals
  3. By varying the tuning of an amplifier tank
    circuit to produce PM signals
  4. By varying the tuning of a microphone
    preamplifier to produce AM signals

142
  • E7E05 -- What circuit is added to an FM
    transmitter to boost the higher audio
    frequencies?
  1. A de-emphasis network
  2. A heterodyne suppressor
  3. An audio prescaler
  4. A pre-emphasis network

143
  • E7E06 -- Why is de-emphasis commonly used in FM
    communications receivers?
  1. For compatibility with transmitters using phase
    modulation
  2. To reduce impulse noise reception
  3. For higher efficiency
  4. To remove third-order distortion products

144
  • E7E10 -- How does a diode detector function?
  1. By rectification and filtering of RF signals
  2. By breakdown of the Zener voltage
  3. By mixing signals with noise in the transition
    region of the diode
  4. By sensing the change of reactance in the diode
    with respect to frequency

145
  • E7E11 -- Which of the following types of detector
    is well suited for demodulating SSB signals?
  1. Discriminator
  2. Phase detector
  3. Product detector
  4. Phase comparator

146
  • E7E12 -- What is a frequency discriminator stage
    in a FM receiver?
  1. An FM generator circuit
  2. A circuit for filtering two closely adjacent
    signals
  3. An automatic band-switching circuit
  4. A circuit for detecting FM signals

147
Digital Signal Processing and Software Defined
Radio
  • Some modern radios modulate and demodulate
    signals entirely in software.
  • This type of radio is called a software-defined
    radio, or SDR.
  • One type of SDR uses a process called direct
    digital conversion to convert
  • the analog radio signal into a series of numbers.
  • As applied to software defined radios, direct
    digital conversion means
  • incoming RF is digitized by an analog-to-digital
    converter without
  • being mixed with a local oscillator signal.

R
148
Digital Signal Processing and Software Defined
Radio
  • Analog-to-digital converter specifications are
    crucial for a software-defined radio.
  • For example, sample rate is the aspect of
    receiver analog-to-digital conversion that
    determines the maximum receive bandwidth of a
    Direct Digital Conversion SDR.
  • An analog signal must be sampled at twice the
    rate of the highest frequency component of the
    signal by an analog-to-digital converter so that
    the signal can be accurately reproduced.

R
149
Digital Signal Processing and Software Defined
Radio
  • Voltage resolution is also important.
  • The reference voltage level and sample width in
    bits sets the minimum detectable signal level for
    an SDR in the absence of atmospheric or thermal
    noise.
  • The minimum number of bits required for an
    analog-to-digital converter to sample a signal
    with a range of 1 volt at a resolution of 1
    millivolt is 10 bits.

R
150
Digital Signal Processing and Software Defined
Radio
  • Modern software defined radios convert an
    incoming signal into two data streams I and Q.
  • The letters I and Q in I/Q modulation (and
    demodulation) represent In-phase and Quadrature.
  • The I and Q data streams are 90 degrees out of
    phase with one another, and as a result, the two
    data streams not only show how the amplitude of a
    signal is changing, but how the phase of a signal
    is changing.
  • The digital process that is applied to I and Q
    signals in order to recover the baseband
    modulation information is the Fast Fourier
    Transform.
  • Converting digital signals from the time domain
    to the frequency domain is the function that a
    Fast Fourier Transform performs.

R
151
Digital Signal Processing and Software Defined
Radio
  • Once a signal has been digitized, or converted
    into a series of numbers, it can be digitally
    filtered.
  • The kind of digital signal processing audio
    filter used to remove unwanted noise from a
    received SSB signal is an adaptive filter.
  • Another type of digital filter, one that is
    often used in a direct digital conversion
    receiver, is the finite impulse, or FIR, filter.
  • An advantage of a Finite Impulse Response (FIR)
    filter vs an Infinite Impulse Response (IIR)
    digital filter is that FIR filters delay all
    frequency components of the signal by the same
    amount.

R
152
Digital Signal Processing and Software Defined
Radio
  • The FIR filter in a software defined radio might
    also be a decimating filter.
  • The decimation function reduces the effective
    sample rate by removing samples when using a
    digital filter.
  • SDRs perform decimation because the signal of
    interest will usually have a significantly lower
    bandwidth than the digitized signal, and reducing
    the sample rate allows SDRs to use less-powerful
    processors.
  • One way the sampling rate of an existing digital
    signal might be adjusted by a factor of 3/4 is to
    interpolate by a factor of three, then decimate
    by a factor of four.

R
153
Digital Signal Processing and Software Defined
Radio
  • An anti-aliasing digital filter is required in a
    digital decimator because it removes
    high-frequency signal components which would
    otherwise be reproduced as lower frequency
    components.
  • Taps in a digital signal processing filter
    provide incremental signal delays for filter
    algorithms. (More taps would allow a digital
    signal processing filter to create a sharper
    filter response.
  • Signals can also be generated using SDR
    techniques. A common method of generating an SSB
    signal using digital signal processing is to
    combine signals with a quadrature phase
    relationship.
  • The type of digital signal processing filter used
    to generate an SSB signal is a Hilbert-transform
    filter.

R
154
So, what is SDR?
  • Software-defined not software-controlled radio
  • Most of the complex signal handling using DSP
  • RF Spectrum and waterfall displays using FFT
  • User interface through computer

R
155
Software Defined Radio
  • Usually some form of direct conversion
  • RF to baseband with no IF
  • RF band pass filtering is required to avoid
    images and birdies
  • IF band pass filtering equivalent, demodulation,
    amplification, detectors, noise reduction, noise
    blanking, etc. are all done in software
  • Usually requires a PC to run software and control
    the receiver/transmitter

R
156
Software Defined Radio
R
157
Software Defined Radio
R
158
  • E8A11 What type of information can be conveyed
    using digital waveforms?
  1. Human speech
  2. Video signals
  3. Data
  4. All of these choices are correct

159
  • E8A12 What is an advantage of using digital
    signals instead of analog signals to convey the
    same information?
  1. Less complex circuitry is required for digital
    signal generation and detection
  2. Digital signals always occupy a narrower
    bandwidth
  3. Digital signals can be regenerated multiple times
    without error
  4. All of these choices are correct

160
  • E8A13 Which of these methods is commonly used
    to convert analog signals to digital signals?
  1. Sequential sampling
  2. Harmonic regeneration
  3. Level shifting
  4. Phase reversal

161
  • E7F05 How frequently must an analog signal be
    sampled by an analog-to-digital converted so that
    the signal can be accurately reproduced?
  1. At half the rate of the highest frequency
    component of the signal
  2. At twice the rate of highest frequency component
    of the signal
  3. At the same rate as the highest frequency
    component of the signal
  4. At four times the rate of the highest frequency
    component of the signal

162
  • E8A09 How many levels can an analog-to-digital
    converter with 8 bit resolution encode?
  1. 8
  2. 8 multiplied by the gain of the input amplifier
  3. 256 divided by the gain of the input amplifier
  4. 256

163
  • E8A04 -- What is dither with respect to digital
    to analog converters?
  1. An abnormal condition where the converter cannot
    settle on a value to represent the signal
  2. A small amount of noise added to the input signal
    to allow more precise representation of a signal
    over time
  3. An error caused by irregular quantization step
    size
  4. A method of decimation by randomly skipping
    samples

164
  • E7F11 -- What sets the minimum detectable signal
    level for an SDR in the absence of atmospheric or
    thermal noise?
  1. Sample clock phase noise
  2. Reference voltage level and sample width in bits
  3. Data storage transfer rates
  4. Missing codes and jitter

165
  • E8A10 What is the purpose of a low pass filter
    used in conjunction with a digital-to-analog
    converter?
  1. Lower the input bandwidth to increase the
    effective resolution
  2. Improve accuracy by removing out of sequence
    codes from the input
  3. Remove harmonics from the output caused by the
    discrete analog levels generated
  4. All of these choices are correct

166
  • E8A01 -- What is the name of the process that
    shows that a square wave is made up of a sine
    wave plus all of its odd harmonics its odd
    harmonics?
  1. Fourier analysis
  2. Vector analysis
  3. Numerical analysis
  4. Differential analysis

167
  • E7F07 -- What function can a Fast Fourier
    Transform perform?
  1. Converting analog signals to digital form
  2. Converting digital signals to analog form
  3. Converting digital signals
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