Amateur Extra License Class

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Amateur Extra License Class

• Chapter 6
• Electronic Circuits

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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.

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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.

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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

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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.

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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.

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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.

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Amplifiers

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

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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.

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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.

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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.

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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

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Amplifiers
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Amplifiers
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Amplifiers

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

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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.

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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.

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Amplifiers
LM741
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Amplifiers

• Op Amp Amplifiers
• Inverting Amplifier.

Gain RF / RIN
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Amplifiers

• Operational Amplifiers (Op-Amps).
• Non-inverting Amplifier.

Gain (RF R2) / R2
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Amplifiers

• Operational Amplifiers (Op-Amps).
• Differential Amplifier.

Gain (R3 R1) / R1 or Gain (R4 R2) /
R2 where R1 R2 and R3 R4
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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

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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Amplifiers

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

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Amplifiers

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

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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.

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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.

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Amplifiers

• Instability and Parasitic Oscillation.
• Neutralization.

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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.

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Amplifiers

• Instability and Parasitic Oscillation.
• Parasitic suppressor.

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Amplifiers

• Instability and Parasitic Oscillation.
• Parasitic suppressor.

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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.

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Amplifiers

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

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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.

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Amplifiers

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

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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.

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• 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

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• E7B10 -- In Figure E7-1, what is the purpose of
  R1 and R2?

1. Load resistors
2. Fixed bias
3. Self bias
4. Feedback

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• E7B11 -- In Figure E7-1, what is the purpose of
  R3?

1. Fixed bias
2. Emitter bypass
3. Output load resistor
4. Self bias

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• 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

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• E7B13 -- In Figure E7-2, what is the purpose of R?

1. Emitter load
2. Fixed bias
3. Collector load
4. Voltage regulation

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• 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

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• 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

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• 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

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• E7G03 What is typical input impedance of an
  integrated circuit op-amp?

1. 100 ohms
2. 1000 ohms
3. Very low
4. Very high

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• 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

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• 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

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• 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

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• 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

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• 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

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• 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

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• 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

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• 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

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• 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

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• 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

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• 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

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• 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

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• 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

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• 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

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• 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

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• 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

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• 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

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• 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

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• 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

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Break
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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.

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Signal Processing

• Oscillator Circuits Characteristics.
• Colpitts oscillator.
• Tapped capacitance.
• Hartley oscillator.
• Tapped inductance.

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Signal Processing

• Oscillator Circuits Characteristics.
• Pierce oscillator.
• Tuned circuit replaced
• with a crystal.

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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.

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Signal Processing

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

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Signal Processing

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

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Signal Processing

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

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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.

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Signal Processing

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

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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.

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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

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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

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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.

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Signal Processing

• Mixers

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Signal Processing

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

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Signal Processing

• Mixers
• Single-balanced mixer.

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Signal Processing

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

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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.

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Signal Processing

• Mixers
• Dual-gate MOSFET mixer.

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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.

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Signal Processing

• Modulators
• Amplitude modulation.
• Multiplying (mixing) AF signal carrier produces
  amplitude modulated signal.

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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.

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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.

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Signal Processing

• Modulators
• Single-sideband modulation.
• Phasing (quadrature) method.

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Signal Processing

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

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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.

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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.

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Signal Processing

• Detectors and Demodulators
• Detectors.
• Simplest detector is the diode detector.
• a.k.a. Envelope detector.

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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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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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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