Amateur Extra License Class

Amateur Extra License Class

Chapter 7

Radio Signals and Measurements

Types of Waveforms

• Sine Waves• Most basic type of waveform.• Occur often in nature.

• Pendulum.• Weight on spring.• Point on rim of wheel.

Types of Waveforms

• Sine waves• Contains only one frequency.• Cycle = One complete set of values

before they repeat.• Cycle = One complete rotation of

vector (360°).• Frequency = Number of cycles per

second.• Period = Time to complete one

cycle.

Types of Waveforms

• Complex Waveforms• Waveforms that contain more than one frequency.• Regular waves.

• More properly called “periodic” waves.• Repeat at a regular interval.

• Made up of a fundamental & its harmonics.

• Irregular waves.• Non-periodic.

• Human speech.

• Easily visualized in frequency domain.

Types of Waveforms

• Sawtooth Wave• Fundamental and all harmonics.• Amplitude of harmonics decrease with increasing

frequency.f1 + f2/2 + f3/3 + f4/4 + f5/5 + ………..

Types of Waveforms

• Square Wave• Fundamental and all odd harmonics.• Amplitude of harmonics decrease with increasing

frequency.f1 + f3/3 + f5/5 + f7/7 + f9/9 + ………..

Types of Waveforms

• Rectangular Wave• Square wave where on & off times are not equal.

• Pulse Wave• Rectangular wave where position, width, and/or

amplitude of pulses varies.• In radio communications, often narrow pulses with

wide gaps between pulses.

E8A01 -- What type of wave is made up of a sine wave plus all of its odd harmonics?

A. A square waveB. A sine waveC. A cosine waveD. A tangent wave

E8A02 -- What type of wave has a rise time significantly faster than its fall time (or vice versa)?

A. A cosine waveB. A square waveC. A sawtooth waveD. A sine wave

E8A03 -- What type of wave is made up of sine waves of a given fundamental frequency plus all its harmonics?

A. A sawtooth waveB. A square waveC. A sine waveD. A cosine wave

E8A08 -- What is the period of a wave?

A. The time required to complete one cycleB. The number of degrees in one cycleC. The number of zero crossings in one cycleD. The amplitude of the wave

E8A09 -- What type of waveform is produced by human speech?

A. SinusoidalB. LogarithmicC. IrregularD. Trapezoidal

E8A10 -- Which of the following is a distinguishing characteristic of a pulse waveform?

A. Regular sinusoidal oscillationsB. Narrow bursts of energy separated by periods

of no signalC. A series of tones that vary between two

frequenciesD. A signal that contains three or more discrete

tones

AC Waveforms and Measurements

• AC Measurements• DC voltmeter/ammeter will

read the average voltage/current, which is zero.

• With an oscilloscope, it is easy to read the maximum voltage/current.

1 = Peak2 = Peak-to-Peak3 = Root-Mean-Square (RMS)


• AC Measurements• An AC current will heat up a

resistor.• The amount of DC current that

causes the same amount of heating is the root-mean-square (RMS) value.

• VRMS = 0.707 x VPeak1 = Peak2 = Peak-to-Peak3 = Root-Mean-Square (RMS)


• AC MeasurementsTo Calculate Sine Wave Square Wave

RMS 0.707 x Peak Peak

Peak 1.414 x RMS RMS


• AC Power• Voltage & Current In-Phase

• PAVG = PRMS = VRMS x IRMS

• PPeak = VPeak x IPeak = 2 x PRMS

E8A04 -- What is equivalent to the root-mean-square value of an AC voltage?

A. The AC voltage found by taking the square of the average value of the peak AC voltage

B. The DC voltage causing the same amount of heating in a given resistor as the corresponding peak AC voltage

C. The DC voltage causing the same amount of heating in a resistor as the corresponding RMS AC voltage

D. The AC voltage found by taking the square root of the average AC value

E8A05 -- What would be the most accurate way of measuring the RMS voltage of a complex waveform?

A. By using a grid dip meterB. By measuring the voltage with a D'Arsonval

meterC. By using an absorption wavemeterD. By measuring the heating effect in a known

resistor

E8D02 -- What is the relationship between the peak-to-peak voltage and the peak voltage amplitude of a symmetrical waveform?

A. 0.707:1B. 2:1C. 1.414:1D. 4:1

E8D03 -- What input-amplitude parameter is valuable in evaluating the signal-handling capability of a Class A amplifier?

A. Peak voltageB. RMS voltageC. Average powerD. Resting voltage

E8D05 -- If an RMS-reading AC voltmeter reads 65 volts on a sinusoidal waveform, what is the peak-to-peak voltage?

A. 46 voltsB. 92 voltsC. 130 voltsD. 184 volts

E8D12 -- What is the peak voltage of a sinusoidal waveform if an RMS-reading voltmeter reads 34 volts?


E8D13 -- Which of the following is a typical value for the peak voltage at a standard U.S. household electrical outlet?


E8D14 -- Which of the following is a typical value for the peak-to-peak voltage at a standard U.S. household electrical outlet?


E8D15 -- Which of the following is a typical value for the RMS voltage at a standard U.S. household electrical power outlet?

A. 120V ACB. 340V ACC. 85V ACD. 170V AC

E8D16 -- What is the RMS value of a 340-volt peak-to-peak pure sine wave?

A. 120V ACB. 170V ACC. 240V ACD. 300V AC


• Power of Modulated RF Signals• In an unmodulated RF signal, the average power

can be calculated from:• PAVG = VRMS

2 / Z


• Power of Modulated RF Signals• If the signal is modulated, the situation is more

complex.• CW, FM, & some digital modes have a constant

amplitude & the average power is the same as if the carrier was not modulated.

• For other modes, it is more useful to use the peak envelope power (PEP) of the signal.


• Power of Modulated RF Signals• Modulated RF signals.

• Peak-Envelope-Power (PEP).• Measure peak voltage.• PPEP = (0.707 x VPeak)2 / RL

• Average Power.• Long term average of power output.

• Crest Factor.• Ratio of PEP to average power.• SSB typically 2.5:1.

• 40%

E8A06 -- What is the approximate ratio of PEP-to-average power in a typical single-sideband phone signal?

A. 2.5 to 1B. 25 to 1C. 1 to 1D. 100 to 1

E8A07 -- What determines the PEP-to-average power ratio of a single-sideband phone signal?

A. The frequency of the modulating signalB. The characteristics of the modulating signalC. The degree of carrier suppressionD. The amplifier gain

E8D04 -- What is the PEP output of a transmitter that develops a peak voltage of 30 volts into a 50-ohm load?

A. 4.5 wattsB. 9 wattsC. 16 wattsD. 18 watts

E8D06 -- What is the advantage of using a peak-reading wattmeter to monitor the output of a SSB phone transmitter?

A. It is easier to determine the correct tuning of the output circuit

B. It gives a more accurate display of the PEP output when modulation is present

C. It makes it easier to detect high SWR on the feed line

D. It can determine if any flat-topping is present during modulation peaks

E8D10 -- What type of meter should be used to monitor the output signal of a voice-modulated single-sideband transmitter to ensure you do not exceed the maximum allowable power?

A. An SWR meter reading in the forward direction

B. A modulation meterC. An average reading wattmeterD. A peak-reading wattmeter

E8D11 -- What is the average power dissipated by a 50-ohm resistive load during one complete RF cycle having a peak voltage of 35 volts?

A. 12.2 wattsB. 9.9 wattsC. 24.5 wattsD. 16 watts


• Electromagnetic Fields• Electric field & magnetic

field oscillating at right angles to each other.

• Travels through free space at the speed of light.

• 186,000 miles/second.• 300 million meters/second.


• Electromagnetic Fields• Polarization.

• Defined by direction of electric field.• Horizontal polarization Horizontal electric field.• Vertical polarization Vertical electric field.• Circular polarization Rotating electric field.

E8D07 -- What is an electromagnetic wave?

A. Alternating currents in the core of an electromagnet

B. A wave consisting of two electric fields at right angles to each other

C. A wave consisting of an electric field and a magnetic field oscillating at right angles to each other

D. A wave consisting of two magnetic fields at right angles to each other

E8D08 -- Which of the following best describes electromagnetic waves traveling in free space?

A. Electric and magnetic fields become aligned as they travel

B. The energy propagates through a medium with a high refractive index

C. The waves are reflected by the ionosphere and return to their source

D. Changing electric and magnetic fields propagate the energy

E8D09 -- What is meant by circularly polarized electromagnetic waves?

A. Waves with an electric field bent into a circular shape

B. Waves with a rotating electric fieldC. Waves that circle the EarthD. Waves produced by a loop antenna

Test Equipment

• Instruments and Accuracy• Multimeters.

• a.k.a. – VOM, DVM, VTVM.• Accuracy expressed in % of full scale.

• If accuracy is 2% of full scale on 100 mA scale, then accuracy is +2 mA.

• Resolution expressed in digits.• Typically 3 ½ digits (0.000 to 1.999)• 3 ½ digit 0.05% resolution.

• DO NOT CONFUSE RESOLUTION WITH ACCURACY!

Test Equipment

• Instruments and Accuracy• Analog Multimeters.

• D’Arsonval movement.• Rotating coil suspended between

permanent magnets.• When current flows in coil, coil rotates

moving needle across scale.• Coil impedance affects accuracy.

• Sensitivity expressed in Ohms/Volt.• 20,000 Ω/V very good analog meter.

Test Equipment

• Instruments and Accuracy• Vacuum Tube Voltmeters (VTVM).

• D’Arsonval movement.• Used vacuum tube amplifier to

improve sensitivity.• Typically 10 megΩ/V or greater.

Test Equipment

• Instruments and Accuracy• Digital Multimeters (DVM).

• Digital display.• Use FET amplifier to improve

sensitivity.• Typically 10 megΩ/V or greater.

Test Equipment

• Instruments and Accuracy• Dip Meters.

• Oscillator with fixed external inductor & variable capacitor.

• External coil is coupled to an unknown tuned circuit & capacitor adjusted until “dip” occurs.

• Read resonant frequency from dial.• General reading only – not precision.

Test Equipment

• Instruments and Accuracy• Dip Meters.

• Too “loose” coupling will not produce useable dip.

• Too “tight” coupling will change resonant frequency of circuit being measured.

Test Equipment

• Instruments and Accuracy• Impedance bridges.

• By “balancing” the bridge you can determine value of unknown impedance.

• Null can be achieved very precisely.• “Antenna analyzers” are actually impedance bridges.

Test Equipment

• Instruments and Accuracy• Frequency counter.

• Accuracy dependent on time base• Accuracy expressed in parts per million (ppm).• May use a prescaler.

Test Equipment


• Converts input signal into a series of pulses.• Sometimes prescaler used to lower input frequency.

• Internal oscillator called the “time base” determines accuracy of counter.

Test Equipment


• Direct-count frequency counter• Counts number of pulses during a known time period.• Frequency is calculated from number of pulses & length of

gate pulse.

• Period-measuring frequency counter• Counts number of time base pulses during one input signal

pulse.• Period is calculated from number of time-base pulses during

one input signal pulse.• Improved accuracy for low frequency signals.

E4B01 -- Which of the following factors most affects the accuracy of a frequency counter?

A. Input attenuator accuracyB. Time base accuracyC. Decade divider accuracyD. Temperature coefficient of the logic

E4B02 -- What is an advantage of using a bridge circuit to measure impedance?

A. It provides an excellent match under all conditions

B. It is relatively immune to drift in the signal generator source

C. The measurement is based on obtaining a signal null, which can be done very precisely

D. It can display results directly in Smith chart format

E4B03 -- If a frequency counter with a specified accuracy of +/- 1.0 ppm reads 146,520,000 Hz, what is the most the actual frequency being measured could differ from the reading?

A. 165.2 HzB. 14.652 kHzC. 146.52 HzD. 1.4652 MHz

E4B04 -- If a frequency counter with a specified accuracy of +/- 0.1 ppm reads 146,520,000 Hz, what is the most the actual frequency being measured could differ from the reading?

A. 14.652 HzB. 0.1 MHzC. 1.4652 HzD. 1.4652 kHz

E4B05 -- If a frequency counter with a specified accuracy of +/- 10 ppm reads 146,520,000 Hz, what is the most the actual frequency being measured could differ from the reading?

A. 146.52 HzB. 10 HzC. 146.52 kHzD. 1465.20 Hz

E4B08 -- Which of the following is a characteristic of a good DC voltmeter?

A. High reluctance inputB. Low reluctance inputC. High impedance inputD. Low impedance input

E4B12 -- What is the significance of voltmeter sensitivity expressed in ohms per volt?

A. The full scale reading of the voltmeter multiplied by its ohms per volt rating will provide the input impedance of the voltmeter

B. When used as a galvanometer, the reading in volts multiplied by the ohms/volt will determine the power drawn by the device under test

C. When used as an ohmmeter, the reading in ohms divided by the ohms/volt will determine the voltage applied to the circuit

D. When used as an ammeter, the full scale reading in amps divided by ohms/volt will determine the size of shunt needed

E4B14 -- What happens if a dip meter is too tightly coupled to a tuned circuit being checked?

A. Harmonics are generatedB. A less accurate reading resultsC. Cross modulation occursD. Intermodulation distortion occurs

Test Equipment

• The Oscilloscope• Allows direct observation of high-speed signals &

waveforms.

Test Equipment

• The Oscilloscope• Displays voltage versus time.

• Signal applied to vertical deflection plates.• Sawtooth waveform from time base applied to

horizontal deflection plates.

• Bandwidth of vertical amplifier determines highest frequency signal that can be displayed.

• Sometimes 2 or more vertical amplifiers.• Allows displaying multiple signals simultaneously.

Test Equipment

• The Oscilloscope• Uses a probe to connect signal to the vertical

amplifier.• Each probe has its own ground lead.

• Keep ground leads as short as possible.

• Probes are “compensated” to display high frequency waveforms accurately.

Test Equipment

Probe Compensated Correctly

Test Equipment

Probe Undercompensated

Test Equipment

Probe Overcompensated

Test Equipment

• The Oscilloscope• Easiest value to read using an

oscilloscope is peak-to-peak voltage.

• Can also read:• Peak voltage.• Period.

Test Equipment

Lissajous Pattern

E4A11 -- Which of these instruments could be used for detailed analysis of digital signals?

A. Dip meterB. OscilloscopeC. OhmmeterD. Q meter

E4B07 -- Which of the following is good practice when using an oscilloscope probe?

A. Keep the signal ground connection of the probe as short as possible

B. Never use a high impedance probe to measure a low impedance circuit

C. Never use a DC-coupled probe to measure an AC circuit

D. All of these choices are correct

E4B13 -- How is the compensation of an oscilloscope probe typically adjusted?

A. A square wave is displayed and the probe is adjusted until the horizontal portions of the displayed wave are as nearly flat as possible

B. A high frequency sine wave is displayed and the probe is adjusted for maximum amplitude

C. A frequency standard is displayed and the probe is adjusted until the deflection time is accurate

D. A DC voltage standard is displayed and the probe is adjusted until the displayed voltage is accurate

E8D01 -- Which of the following is the easiest voltage amplitude parameter to measure when viewing a pure sine wave signal on an analog oscilloscope?

A. Peak-to-peak voltageB. RMS voltageC. Average voltageD. DC voltage

Test Equipment

• The Spectrum Analyzer

Test Equipment

• The Spectrum Analyzer• Displays signal amplitude versus frequency.

• An oscilloscope displays signals in the time domain.• Horizontal axis displays time.

• A spectrum analyzer displays signals in the frequency domain.

• Horizontal axis displays frequency.

• Narrow filter swept across a range of frequencies.

• The Spectrum Analyzer• Used for checking output of transmitter or

amplifier for spurs. • Used for checking transmitter intermodulation

distortion (IMD).

Test Equipment

Test Equipment

• The Spectrum Analyzer

Test Equipment

Test Equipment

• Two-tone Intermodulation Distortion (IMD) Test• 2 non-harmonically related tones.

• ARRL Labs uses 700 Hz & 1900 Hz.

E4A01 -- How does a spectrum analyzer differ from an oscilloscope?

A. A spectrum analyzer measures ionospheric reflection; an oscilloscope displays electrical signals

B. A spectrum analyzer displays the peak amplitude of signals; an oscilloscope displays the average amplitude of signals

C. A spectrum analyzer displays signals in the frequency domain; an oscilloscope displays signals in the time domain

D. A spectrum analyzer displays radio frequencies; an oscilloscope displays audio frequencies

E4A02 -- Which of the following parameters would a spectrum analyzer display on the horizontal axis?

A. SWRB. QC. TimeD. Frequency

E4A03 -- Which of the following parameters would a spectrum analyzer display on the vertical axis?

A. AmplitudeB. DurationC. SWRD. Q

E4A04 -- Which of the following test instruments is used to display spurious signals from a radio transmitter?

A. A spectrum analyzerB. A wattmeterC. A logic analyzerD. A time-domain reflectometer

E4A05 -- Which of the following test instruments is used to display intermodulation distortion products in an SSB transmission?

A. A wattmeterB. A spectrum analyzerC. A logic analyzerD. A time-domain reflectometer

E4A06 -- Which of the following could be determined with a spectrum analyzer?

A. The degree of isolation between the input and output ports of a 2 meter duplexer

B. Whether a crystal is operating on its fundamental or overtone frequency

C. The spectral output of a transmitterD. All of these choices are correct

E4A12 -- Which of the following procedures is an important precaution to follow when connecting a spectrum analyzer to a transmitter output?

A. Use high quality double shielded coaxial cables to reduce signal losses

B. Attenuate the transmitter output going to the spectrum analyzer

C. Match the antenna to the loadD. All of these choices are correct

E4B10 -- Which of the following describes a method to measure intermodulation distortion in an SSB transmitter?

A. Modulate the transmitter with two non-harmonically related radio frequencies and observe the RF output with a spectrum analyzer

B. Modulate the transmitter with two non-harmonically related audio frequencies and observe the RF output with a spectrum analyzer

C. Modulate the transmitter with two harmonically related audio frequencies and observe the RF output with a peak reading wattmeter

D. Modulate the transmitter with two harmonically related audio frequencies and observe the RF output with a logic analyzer

• Transistor Circuit Parameters• Some DC voltage measurements are useful for

troubleshooting.• VBE ~ 0.7 VDC (Silicon)

• VBE ~ 0.3 VDC (Germanium)

• VCE ~ 0.5 x VCC

• (If class A amplifier.)

• Other examples in book.

Test Equipment

E4A10 -- Which of the following tests establishes that a silicon NPN junction transistor is biased on?

A. Measure base-to-emitter resistance with an ohmmeter; it should be approximately 6 to 7 ohms

B. Measure base-to-emitter resistance with an ohmmeter; it should be approximately 0.6 to 0.7 ohms

C. Measure base-to-emitter voltage with a voltmeter; it should be approximately 6 to 7 volts

D. Measure base-to-emitter voltage with a voltmeter; it should be approximately 0.6 to 0.7 volts

Modulation Systems

• FCC Emission Designations and Terms• Specified by ITU.

• Either 3 or 7 characters.• If 3 characters:

• 1st Character - type of modulation of the main carrier. • 2nd Character - nature of signal(s) modulating the main carrier. • 3rd Character - type of information to be transmitted.

• If 7 characters, add 4-character bandwidth designator in front of 3-character designator.

Modulation Systems

• FCC Emission Designations and Terms• Type of Modulation.

N Unmodulated Carrier

A Amplitude Modulation

R Single Sideband Reduced Carrier

J Single Sideband Suppressed Carrier

C Vestigial Sideband

F Frequency Modulation

G Phase Modulation

P, K, L, M, Q, V, W, X Various Types of Pulse Modulation

Modulation Systems

• FCC Emission Designations and Terms• Type of Modulating Signal.

0 No modulating signal

1 A single channel containing quantized or digital information without the use of a modulating sub-carrier

2 A single channel containing quantized or digital information with the use of a modulating sub-carrier

3 A single channel containing analogue information

7 Two or more channels containing quantized or digital information

8 Two or more channels containing analogue information

X Cases not otherwise covered

Modulation Systems

• FCC Emission Designations and Terms• Type of Transmitted Information.

N No information transmitted

A Telegraphy - for aural reception

B Telegraphy - for automatic reception

C Facsimile

D Data transmission, telemetry, telecommand

E Telephony (including sound broadcasting)

F Television (video)

W Combination of the above

X Cases not otherwise covered

Modulation Systems

• FCC Emission Designations and Terms• 3-character designator examples:

• A1A = CW.• A3E = Amplitude-modulated phone.• J3E = Single-sideband phone.• F3E = Frequency-modulated phone.• F1B = Radioteletype (RTTY).

Modulation Systems

• FCC Emission Designations and Terms• Emission Types.

• Part 97 refers to emission types rather than emission designators.

Continuous Wave (CW) Modulated CW (MCW)Phone (AM, FM, SSB) Spread Spectrum (SS)Radiotetetype (RTTY) PulseData (Packet, PSK-31, etc.) TestImage (SSTV, Fascimile, etc.)

Modulation Systems

• FM/PM Modulation and Modulators• Amount of frequency change is proportional to

amplitude of modulating signal.• Deviation.

• Speed of frequency change is equal to frequency of modulating signal.

• Need to understand 2 terms to fully describe an FM or PM signal.

• Deviation Ratio.• Modulation Index.

Modulation Systems

• FM/PM Modulation and Modulators• Deviation ratio.

• Deviation Ratio = fDev / fMod

• fDev = Maximum frequency deviation.

• fMod = Maximum modulating frequency.

• Deviation ratio is constant in both an FM modulator and in a PM modulator.

Modulation Systems

• FM/PM Modulation and Modulators• Modulation index.

• Modulation Index = fDev / fm

• fDev = Maximum frequency deviation.

• fm = Instantaneous modulating frequency.

• Modulation index is continuously changing with modulating frequency in an FM modulator.

• Modulation index is constant in a PM modulator.• The FCC Rules limit the modulation index to 1.0 at the

highest modulating frequency. [§97.307(f)(1)]

E1B12 -- What is the highest modulation index permitted at the highest modulation frequency for angle modulation?

A. .5B. 1.0C. 2.0D. 3.0

E8B01 -- What is the term for the ratio between the frequency deviation of an RF carrier wave, and the modulating frequency of its corresponding FM-phone signal?

A. FM compressibilityB. Quieting indexC. Percentage of modulationD. Modulation index

E8B02 -- How does the modulation index of a phase-modulated emission vary with RF carrier frequency (the modulated frequency)?

A. It increases as the RF carrier frequency increases

B. It decreases as the RF carrier frequency increases

C. It varies with the square root of the RF carrier frequency

D. It does not depend on the RF carrier frequency

E8B03 -- What is the modulation index of an FM-phone signal having a maximum frequency deviation of 3000 Hz either side of the carrier frequency, when the modulating frequency is 1000 Hz?A. 3B. 0.3C. 3000D. 1000

E8B04 -- What is the modulation index of an FM-phone signal having a maximum carrier deviation of plus or minus 6 kHz when modulated with a 2-kHz modulating frequency?

A. 6000B. 3C. 2000D. 1/3

E8B05 -- What is the deviation ratio of an FM-phone signal having a maximum frequency swing of plus-or-minus 5 kHz when the maximum modulation frequency is 3 kHz?

A. 60B. 0.167C. 0.6D. 1.67

E8B06 -- What is the deviation ratio of an FM-phone signal having a maximum frequency swing of plus or minus 7.5 kHz when the maximum modulation frequency is 3.5 kHz?

A. 2.14B. 0.214C. 0.47D. 47

E8B09 -- What is meant by deviation ratio?

A. The ratio of the audio modulating frequency to the center carrier frequency

B. The ratio of the maximum carrier frequency deviation to the highest audio modulating frequency

C. The ratio of the carrier center frequency to the audio modulating frequency

D. The ratio of the highest audio modulating frequency to the average audio modulating frequency

Modulation Systems

• Pulse Modulation Systems.• Series of widely spaced short pulses.• Peak power greater than average power.

• Signal duty cycle < 100%.

• Often used for data transmission.

Modulation Systems

• Pulse Modulation Systems.• Types of pulse modulation.

• Pulse amplitude modulation (PAM).• Pulse width modulation (PWM).

• a.k.a. – Pulse duration modulation (PDM).

• Pulse position modulation (PPM). • Pulse code modulation (PCM).

Modulation Systems

• Pulse Modulation Systems.• Pulse amplitude modulation (PAM).

• Varies amplitude of pulses.

Modulation Systems

• Pulse Modulation Systems.• Pulse width modulation (PWM).

• Varies width of pulses.

Modulation Systems

• Pulse Modulation Systems.• Pulse position modulation (PPM).

• Varies time at which pulses occur.

Modulation Systems

• Pulse Modulation Systems.• Pulse code modulation (PCM).

• Transmits series of binary-coded pulses.

E8A11 -- What is one use for a pulse modulated signal?

A. Linear amplificationB. PSK31 data transmissionC. Multiphase power transmissionD. Digital data transmission

E8B07 -- When using a pulse-width modulation system, why is the transmitter's peak power greater than its average power?

A. The signal duty cycle is less than 100%B. The signal reaches peak amplitude only when

voice modulatedC. The signal reaches peak amplitude only when

voltage spikes are generated within the modulator

D. The signal reaches peak amplitude only when the pulses are also amplitude modulated

E8B08 -- What parameter does the modulating signal vary in a pulse-position modulation system?

A. The number of pulses per secondB. The amplitude of the pulsesC. The duration of the pulsesD. The time at which each pulse occurs

Modulation Systems

• Multiplexing.• Transmitting multiple, independent signals on one

carrier.

Modulation Systems

• Multiplexing.• Frequency-division multiplexing.

• One or more “sub-carriers”, each carrying a different signal.

• Commercial FM broadcast SCA.• VHF Omni-Range (VOR).• Fiber optics.

Modulation Systems

• Multiplexing.• Time-division multiplexing.

• Signals are sampled & samples from each signal are interleaved in sequential time slots.

• Normally digital transmission.• Telemetry.

E8B10 -- Which of these methods can be used to combine several separate analog information streams into a single analog radio frequency signal?

A. Frequency shift keyingB. A diversity combinerC. Frequency division multiplexingD. Pulse compression

E8B11 -- Which of the following describes frequency division multiplexing?

A. The transmitted signal jumps from band to band at a predetermined rate

B. Two or more information streams are merged into a "baseband", which then modulates the transmitter

C. The transmitted signal is divided into packets of information

D. Two or more information streams are merged into a digital combiner, which then pulse position modulates the transmitter

E8B12 -- What is digital time division multiplexing?

A. Two or more data streams are assigned to discrete sub-carriers on an FM transmitter

B. Two or more signals are arranged to share discrete time slots of a data transmission

C. Two or more data streams share the same channel by transmitting time of transmission as the sub-carrier

D. Two or more signals are quadrature modulated to increase bandwidth efficiency

Interference and Noise

• Intermodulation• Non-linear circuits or components can act as

mixers to generate signals at the sums & differences of the signals being mixed.

• Unwanted signal can be heard along with wanted signal.

• Signals can also mix in corroded metal junctions or junctions of dissimilar metals.


• Transmitter Intermodulation• Signals can mix in the output stage of a

transmitter.• The IMD products can be transmitted along with the

desired signal.• Low-pass or high-pass filters are NOT effective.• Circulators & isolators are used.

• Ferrite devices that act like “one-way valves” for RF.

• Cavity resonators.

E4D03 -- How can intermodulation interference between two repeaters occur?

A. When the repeaters are in close proximity and the signals cause feedback in the final amplifier of one or both transmitters

B. When the repeaters are in close proximity and the signals mix in the final amplifier of one or both transmitters

C. When the signals from the transmitters are reflected out of phase from airplanes passing overhead

D. When the signals from the transmitters are reflected in phase from airplanes passing overhead

E4D04 -- Which of the following may reduce or eliminate intermodulation interference in a repeater caused by another transmitter operating in close proximity?

A. A band-pass filter in the feed line between the transmitter and receiver

B. A properly terminated circulator at the output of the transmitter

C. A Class C final amplifierD. A Class D final amplifier

E4D06 -- What is the term for unwanted signals generated by the mixing of two or more signals?

A. Amplifier desensitizationB. NeutralizationC. Adjacent channel interferenceD. Intermodulation interference

E4D07 -- Which of the following describes the most significant effect of an off-frequency signal when it is causing cross-modulation interference to a desired signal?

A. A large increase in background noiseB. A reduction in apparent signal strength C. The desired signal can no longer be heardD. The off-frequency unwanted signal is heard in

addition to the desired signal

E4D08 -- What causes intermodulation in an electronic circuit?

A. Too little gainB. Lack of neutralizationC. Nonlinear circuits or devicesD. Positive feedback

E4E11 -- Which of the following is the most likely cause if you are hearing combinations of local AM broadcast signals within one or more of the MF or HF ham bands?

A. The broadcast station is transmitting an over-modulated signal

B. Nearby corroded metal joints are mixing and re-radiating the broadcast signals

C. You are receiving sky wave signals from a distant station

D. Your station receiver IF amplifier stage is defective


• Atmospheric Static• Discharge of static electricity in

the atmosphere.• Lightning most visible source of static

discharge, but non-lightning discharges occur all the time.

• Thunderstorm static louder on lower HF bands (160m, 80m, & 40m).

• Can be heard several hundred miles from the source.


• Atmospheric Static• Static noise can occur without a

thunderstorm.• Rain static.• Snow static.• Wind static.

E4E06 -- What is a major cause of atmospheric static?

A. Solar radio frequency emissionsB. ThunderstormsC. Geomagnetic stormsD. Meteor showers


• AC Line Noise• Man-made noise caused by

electric arc.• Electric motors.• Light dimmers.• Neon signs.• Defective doorbell or doorbell

transformer.


• AC Line Noise• Install “brute force” AC line filter in series with

motor power leads.

E4E05 -- How can noise from an electric motor be suppressed?

A. By installing a high pass filter in series with the motor’s power leads

B. By installing a brute-force AC-line filter in series with the motor leads

C. By installing a bypass capacitor in series with the motor leads

D. By using a ground-fault current interrupter in the circuit used to power the motor

E4E13 -- What might be the cause of a loud roaring or buzzing AC line interference that comes and goes at intervals?

A. Arcing contacts in a thermostatically controlled device

B. A defective doorbell or doorbell transformer inside a nearby residence

C. A malfunctioning illuminated advertising display



• Locating Noise and Interference Sources• Interference from inside building usually

conducted through AC power wiring.• Inside your house.• Outside your house.


• Locating Noise and Interference Sources• To determine if noise is generated within your

own house, pull main breaker & listen on a battery-operated receiver.

• Not FM receiver.

• Restore power & make certain noise returns.• Offending device may need to be powered on for a

while before generating noise.

• Remove power one circuit at a time until noise disappears.


• Locating Noise and Interference Sources• Interference from outside building usually picked up

by antenna or transmission line.• Use “fox hunting” techniques to locate source.


• Locating Noise and Interference Sources• Your transmitter can couple RF into AC and/or

telephone wiring & cause interference to other devices.

• Common mode signals.• RF flowing in same direction on both conductors.• Install common mode choke.

• Several turns of wire around ferrite toroid core.


• Locating Noise and Interference Sources• Computer & networking devices.

• Unstable modulated or unmodulated signals at specific frequencies.

• Switching power supplies.• Series of signals spaced at regular intervals over a wide

spectrum.

• Touch-controlled devices.• Same as above plus signals that sound like AC hum that

may drift slowly across the band.


• Locating Noise and Interference Sources• Plasma TV’s.

E4E07 -- How can you determine if line noise interference is being generated within your home?

A. By checking the power line voltage with a time domain reflectometer

B. By observing the AC power line waveform with an oscilloscope

C. By turning off the AC power line main circuit breaker and listening on a battery operated radio

D. By observing the AC power line voltage with a spectrum analyzer

E4E08 -- What type of signal is picked up by electrical wiring near a radio antenna?

A. A common-mode signal at the frequency of the radio transmitter

B. An electrical-sparking signalC. A differential-mode signal at the AC power

line frequencyD. Harmonics of the AC power line frequency

E4E10 -- What is a common characteristic of interference caused by a touch controlled electrical device?

A. The interfering signal sounds like AC hum on an AM receiver or a carrier modulated by 60 Hz hum on a SSB or CW receiver

B. The interfering signal may drift slowly across the HF spectrum

C. The interfering signal can be several kHz in width and usually repeats at regular intervals across a HF band


E4E14 -- What is one type of electrical interference that might be caused by the operation of a nearby personal computer?

A. A loud AC hum in the audio output of your station receiver

B. A clicking noise at intervals of a few secondsC. The appearance of unstable modulated or

unmodulated signals at specific frequenciesD. A whining type noise that continually pulses

off and on


• Automotive Noise• Vehicular System Noise

• Ignition system noise.• Pre-1975.

• Resistance spark plugs.• High-resistance spark plug cables.• Shielded cables.

• 1975 & later.• High resistance plugs & cables can degrade engine performance.



• Charging system noise.• High-pitched whine or buzz.• Changes frequency with engine speed.• Radiated & picked up by antenna.• Conducted through power wiring.• Connect radio power leads directly to battery.

• Fuse EACH lead.• Add coaxial capacitors in alternator leads.

• a.k.a. – Feed-through capacitors.



• Instrument noise.• Some instruments can generate RF noise.

• Install 0.5 μF coaxial capacitor at the sender element.• Wiper, fuel pump, & other motors can generate RF noise.

• Install 0.25 μF capacitor across the motor winding.

E4E04 -- How can conducted and radiated noise caused by an automobile alternator be suppressed?

A. By installing filter capacitors in series with the DC power lead and by installing a blocking capacitor in the field lead

B. By installing a noise suppression resistor and a blocking capacitor in both leads

C. By installing a high-pass filter in series with the radio's power lead and a low-pass filter in parallel with the field lead

D. By connecting the radio's power leads directly to the battery and by installing coaxial capacitors in line with the alternator leads


• Noise Reduction• Noise Blankers

• Detects noise pulse & interrupts signal during duration of pulse.

• a.k.a. – Gating.• Particularly effective for power line or ignition noise.• Must see signals that appear across a wide bandwidth.• Strong nearby signals may appear excessively wide.


• Noise Reduction• DSP Noise Reduction.

• Use adaptive filter techniques.• Looks for signals that have characteristics of CW or SSB signals

& remove everything else.

• Works well with ALL types of noise & interference.


• Noise Reduction• DSP Noise Reduction.

• Automatic Notch Filters (ANF).• Very effective in eliminating interference from a strong steady

signal (carrier) in the receive passband.• Not recommended for copying CW or low data rate digital

signals.• A good ANF will ”notch out” the desired signal.

E4E01 -- Which of the following types of receiver noise can often be reduced by use of a receiver noise blanker?

A. Ignition noiseB. Broadband white noiseC. Heterodyne interferenceD. All of these choices are correct

E4E02 -- Which of the following types of receiver noise can often be reduced with a DSP noise filter?

A. Broadband white noiseB. Ignition noiseC. Power line noiseD. All of these choices are correct

E4E03 -- Which of the following signals might a receiver noise blanker be able to remove from desired signals?

A. Signals which are constant at all IF levelsB. Signals which appear across a wide

bandwidthC. Signals which appear at one IF but not

anotherD. Signals which have a sharply peaked

frequency distribution

E4E09 -- What undesirable effect can occur when using an IF noise blanker?

A. Received audio in the speech range might have an echo effect

B. The audio frequency bandwidth of the received signal might be compressed

C. Nearby signals may appear to be excessively wide even if they meet emission standards

D. FM signals can no longer be demodulated

E4E12 -- What is one disadvantage of using some types of automatic DSP notch-filters when attempting to copy CW signals?

A. The DSP filter can remove the desired signal at the same time as it removes interfering signals

B. Any nearby signal passing through the DSP system will overwhelm the desired signal

C. Received CW signals will appear to be modulated at the DSP clock frequency

D. Ringing in the DSP filter will completely remove the spaces between the CW characters

Questions?

Amateur Extra License Class

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