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 square wave A sine wave A cosine wave A tangent wave

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

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

E8A08 -- What is the period of a wave? The time required to complete one cycle The number of degrees in one cycle The number of zero crossings in one cycle The amplitude of the wave

E8A09 -- What type of waveform is produced by human speech? Sinusoidal Logarithmic Irregular Trapezoidal

E8A10 -- Which of the following is a distinguishing characteristic of a pulse waveform? Regular sinusoidal oscillations Narrow bursts of energy separated by periods of no signal A series of tones that vary between two frequencies 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 = Peak 2 = Peak-to-Peak 3 = Root-Mean-Square (RMS)

AC Waveforms and Measurements • 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 VPeak 1 = Peak 2 = Peak-to-Peak 3 = Root-Mean-Square (RMS)

AC Waveforms and Measurements • AC Measurements

AC Waveforms and Measurements • 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? The AC voltage found by taking the square of the average value of the peak AC voltage The DC voltage causing the same amount of heating in a given resistor as the corresponding peak AC voltage The DC voltage causing the same amount of heating in a resistor as the corresponding RMS AC voltage 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? By using a grid dip meter By measuring the voltage with a D'Arsonval meter By using an absorption wavemeter 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? 0.707:1 2:1 1.414:1 4:1

E8D03 -- What input-amplitude parameter is valuable in evaluating the signal-handling capability of a Class A amplifier? Peak voltage RMS voltage Average power Resting voltage

E8D05 -- If an RMS-reading AC voltmeter reads 65 volts on a sinusoidal waveform, what is the peak-to-peak voltage? 46 volts 92 volts 130 volts 184 volts

E8D12 -- What is the peak voltage of a sinusoidal waveform if an RMS-reading voltmeter reads 34 volts? 123 volts 96 volts 55 volts 48 volts

E8D13 -- Which of the following is a typical value for the peak voltage at a standard U.S. household electrical outlet? 240 volts 170 volts 120 volts 340 volts

E8D14 -- Which of the following is a typical value for the peak-to-peak voltage at a standard U.S. household electrical outlet? 240 volts 120 volts 340 volts 170 volts

E8D15 -- Which of the following is a typical value for the RMS voltage at a standard U.S. household electrical power outlet? 120V AC 340V AC 85V AC 170V AC

E8D16 -- What is the RMS value of a 340-volt peak-to-peak pure sine wave? 120V AC 170V AC 240V AC 300V AC

AC Waveforms and Measurements • Power of Modulated RF Signals • In an unmodulated RF signal, the average power can be calculated from: • PAVG = VRMS2 / Z

AC Waveforms and Measurements • 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.

AC Waveforms and Measurements • 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? 2.5 to 1 25 to 1 1 to 1 100 to 1

E8A07 -- What determines the PEP-to-average power ratio of a single-sideband phone signal? The frequency of the modulating signal The characteristics of the modulating signal The degree of carrier suppression 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? 4.5 watts 9 watts 16 watts 18 watts

E8D06 -- What is the advantage of using a peak-reading wattmeter to monitor the output of a SSB phone transmitter? It is easier to determine the correct tuning of the output circuit It gives a more accurate display of the PEP output when modulation is present It makes it easier to detect high SWR on the feed line 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? An SWR meter reading in the forward direction A modulation meter An average reading wattmeter 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? 12.2 watts 9.9 watts 24.5 watts 16 watts

AC Waveforms and Measurements • 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.

AC Waveforms and Measurements • 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? Alternating currents in the core of an electromagnet A wave consisting of two electric fields at right angles to each other A wave consisting of an electric field and a magnetic field oscillating at right angles to each other 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? Electric and magnetic fields become aligned as they travel The energy propagates through a medium with a high refractive index The waves are reflected by the ionosphere and return to their source Changing electric and magnetic fields propagate the energy

E8D09 -- What is meant by circularly polarized electromagnetic waves? Waves with an electric field bent into a circular shape Waves with a rotating electric field Waves that circle the Earth 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 • Instruments and Accuracy • Frequency counter. • 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.

Amateur Extra License Class