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 Pulse 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.

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 To Calculate Sine Wave Square Wave RMS 0.707 x Peak Peak 1.414 x RMS

AC Waveforms and Measurements AC Power Voltage & Current In-Phase PAVG = PRMS = VRMS x IRMS PPeak = VPeak x IPeak = 2 x PRMS

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%

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.

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 does a Fourier analysis show to be 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

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

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

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.

Test Equipment Instruments and Accuracy Frequency counter. 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.

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.

Probe Compensated Correctly Test Equipment Probe Compensated Correctly

Probe Undercompensated Test Equipment Probe Undercompensated

Probe Overcompensated 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

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.

Test Equipment The Spectrum Analyzer Used for checking output of transmitter or amplifier for spurs. Used for checking transmitter intermodulation distortion (IMD).

Test Equipment The Spectrum Analyzer

Test Equipment

Test Equipment

Test Equipment

Test Equipment Two-tone Intermodulation Distortion (IMD) Test 2 non-harmonically related tones. ARRL Labs uses 700 Hz & 1900 Hz.

Test Equipment 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.

E4B12 -- What is the significance of voltmeter sensitivity expressed in ohms per volt? The full scale reading of the voltmeter multiplied by its ohms per volt rating will provide the input impedance of the voltmeter When used as a galvanometer, the reading in volts multiplied by the ohms/volt will determine the power drawn by the device under test When used as an ohmmeter, the reading in ohms divided by the ohms/volt will determine the voltage applied to the circuit When used as an ammeter, the full scale reading in amps divided by ohms/volt will determine the size of shunt needed

E4B08 -- Which of the following is a characteristic of a good DC voltmeter? High reluctance input Low reluctance input High impedance input Low impedance input

E4B14 -- What happens if a dip meter is too tightly coupled to a tuned circuit being checked? Harmonics are generated A less accurate reading results Cross modulation occurs Intermodulation distortion occurs

E4B02 -- What is an advantage of using a bridge circuit to measure impedance? It provides an excellent match under all conditions It is relatively immune to drift in the signal generator source It is very precise in obtaining a signal null It can display results directly in Smith chart format

E4A14 – What is the purpose of the prescaler function on a frequency counter? It amplifies the low level signals for more accurate counting It multiplies a higher frequency signal so a low-frequency counter can display the operating frequency It prevents oscillation in a low-frequency counter circuit It divides a higher frequency signal so a low-frequency counter can display the input frequency

E4B01 -- Which of the following factors most affects the accuracy of a frequency counter? Input attenuator accuracy Time base accuracy Decade divider accuracy Temperature coefficient of the logic

E4A15 -- What is an advantage of a period-measuring frequency counter over a direct-count type? It can run on battery power for remote measurements It does not require an expensive high-precision time base It provides improved resolution of low-frequency signals within a comparable time period It can directly measure the modulation index of an FM transmitter

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? 146.52 Hz 10 Hz 146.52 kHz 1465.20 Hz

E4B04 -- If a frequency counter with a specified accuracy of +/- 0 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? 14.652 Hz 0.1 MHz 1.4652 Hz 1.4652 kHz

E4B03 -- If a frequency counter with a specified accuracy of +/- 1 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? 165.2 Hz 14.652 kHz 146.52 Hz 1.4652 MHz

KILL E4A11 -- Which of these instruments could be used for detailed analysis of digital signals? Dip meter Oscilloscope Ohmmeter Q meter

E4A11 – Which of the following is good practice when using an oscilloscope probe? Keep the signal ground connection of the probe as short as possible Never use a high impedance probe to measure a low impedance circuit Never use a DC-coupled probe to measure an AC circuit All of these choices are correct

E4A13 – How is the compensation of an oscilloscope probe typically adjusted? A square wave is displayed and the probe is adjusted until the horizontal portions of the displayed wave are nearly flat as possible A high frequency sine wave is displayed and the probe is adjusted for maximum amplitude A frequency standard is displayed and the probe is adjusted until the deflection time is accurate A DC voltage standard is displayed and the probe is adjusted until the displayed voltage is accurate

KILL E4A01 -- How does a spectrum analyzer differ from an oscilloscope? A spectrum analyzer measures ionospheric reflection; an oscilloscope displays electrical signals A spectrum analyzer displays the peak amplitude of signals; an oscilloscope displays the average amplitude of signals A spectrum analyzer displays signals in the frequency domain; an oscilloscope displays signals in the time domain A spectrum analyzer displays radio frequencies; an oscilloscope displays audio frequencies

E4A01 – Which of the following parameters determines the bandwidth of a digital or computer-based oscilloscope? Input capacitance Input impedance Sampling rate Sample resolution

KILL E4A04 -- Which of the following test instruments is used to display spurious signals from a radio transmitter? A spectrum analyzer A wattmeter A logic analyzer A time-domain reflectometer

E4A04 – What determines the upper frequency limit for a computer soundcard-based oscilloscope program? Analog-to-digital conversion spped of the soundcard Amount of memory on the soundcard Q of the interface of the interface circuit All of these choices are correct

KILL E4A09 -- Which of the following describes a good method for measuring the intermodulation distortion of your own PSK signal? Transmit into a dummy load, receive the signal on a second receiver, and feed the audio into the sound card of a computer running an appropriate PSK program Multiply the ALC level on the transmitter during a normal transmission by the average power output Use an RF voltmeter coupled to the transmitter output using appropriate isolation to prevent damage to the meter All of these choices are correct

E4A09 – When using a computer’s soundcard input to digitize signals, what is the highest frequency signal that can be digitized without aliasing? The same as the sample rate One-half the sample rate One-tenth the sample rate It depends on how the data is stored internally

KILL E4A06 -- Which of the following could be determined with a spectrum analyzer? The degree of isolation between the input and output ports of a 2 meter duplexer Whether a crystal is operating on its fundamental or overtone frequency The spectral output of a transmitter All of these choices are correct

E4A06 -- What is the effect of aliasing in a digital or computer-based oscilloscope? False signals are displayed All signals will have a DC soffset Calibration of the vertical scale is no longer valid False triggering occurs

KILL E4A05 -- Which of the following test instruments is used to display intermodulation distortion products in an SSB transmission? A wattmeter A spectrum analyzer A logic analyzer A time-domain reflectometer

E4A05 – What might be an advantage of a digital vs E4A05 – What might be an advantage of a digital vs. an analog oscilloscope? Automatic amplitude and frequency numerical readout Storage of traces for future reference Manipulation of time base after trace capture All of these choice are correct

KILL E4A10 -- Which of the following tests establishes that a silicon NPN junction transistor is biased on? Measure base-to-emitter resistance with an ohmmeter; it should be approximately 6 to 7 ohms Measure base-to-emitter resistance with an ohmmeter; it should be approximately 0.6 to 0.7 ohms Measure base-to-emitter voltage with a voltmeter; it should be approximately 6 to 7 volts Measure base-to-emitter voltage with a voltmeter; it should be approximately 0.6 to 0.7 volts

E4A10 -- Which of the following displays multiple digital signal states simultaneously? Network analyzer Bit error rate tester Modulation monitor Logic analyzer

KILL E4A02 -- Which of the following parameters would a spectrum analyzer display on the horizontal axis? SWR Q Time Frequency

E4A02 -- Which of the following parameters would a spectrum analyzer display on the horizontal and vertical axes? RF amplitude and time RF amplitude and frequency SWR and frequency SWR and time

KILL E4A03 -- Which of the following parameters would a spectrum analyzer display on the vertical axis? Amplitude Duration SWR Q

E4A03 -- Which of the following test instruments is used to display spurious signals and/or intermodulation distortion products in an SSB transmitter? A wattmeter A spectrum analyzer A logic analyzer A time-domain reflectometer

E4A12 – Which of the following procedures is an important precaution to follow when connecting a spectrum analyzer to a transmitter output? Use high quality double shielded coaxial cables to reduce signal losses Attenuate the transmitter output going to the spectrum analyzer Match the antenna to the load All of these choices are correct

E4B10 -- Which of the following describes a method to measure intermodulation distortion in an SSB transmitter? Modulate the transmitter with two non-harmonically related radio frequencies and observe the RF output with a spectrum analyzer Modulate the transmitter with two non-harmonically related audio frequencies and observe the RF output with a spectrum analyzer Modulate the transmitter with two harmonically related audio frequencies and observe the RF output with a peak reading wattmeter Modulate the transmitter with two harmonically related audio frequencies and observe the RF output with a logic analyzer

Receiver Performance Good receiver performance is essential to successful amateur radio communications. “If you can’t hear ‘em, you can’t work ‘em!” The topics we will cover in this section will allow you to intelligently compare receivers based on published specifications and test results.

Receiver Performance Sensitivity and Noise Receiver sensitivity is a measure of how weak a signal a receiver can receive. a.k.a. – Minimum discernible signal (MDS). a.k.a. – Noise floor. Determined by noise figure and bandwidth of receiver.

Receiver Performance Sensitivity and Noise Minimum discernible signal (MDS). Expressed in dBm or μV. 0 dBm = 1 mW into 50Ω load (≈223mV). Theoretical minimum = -174 dBm/Hz. Noise power at the input of an ideal receiver with a bandwidth of 1 Hz at room temperature. -174 dBm ≈ 4 x 10-9 mW ( 4 billionth of a mW).

Receiver Performance Sensitivity and Noise Minimum discernible signal (MDS). At HF frequencies with an antenna attached, MDS is determined by atmospheric noise. At VHF frequencies & up, MDS is determined by noise generated inside the front end of the receiver.

Receiver Performance Sensitivity and Noise Minimum discernible signal (MDS). Calculating MDS. MDS = 10 x log(fBW) – 174. Example: What is the MDS of a 400 Hz bandwidth receiver with a noise floor of -174dB/Hz? 10 x log(400) = 26. MDS = 26 – 174 = -148 dB.

Receiver Performance Sensitivity and Noise Noise figure. The noise figure of a receiver is the difference in dB between the noise output of the receiver with no antenna connected and that of an ideal receiver with the same gain & bandwidth. NF = (Internal Noise) / (Theoretical MDS). “Figure of merit” of a receiver. Typically a “good” VHF or UHF preamplifier has a NF ≈ 2dB. Actual noise floor = (Theoretical MDS) + NF.

Receiver Performance Sensitivity and Noise Signal-to-noise ratio (SNR). SNR = (Input signal power) / (Noise power).

Receiver Performance Image Response 2 different frequencies, when mixed with the local oscillator frequency will result in a signal at the IF frequency. Image frequency is the desired frequency plus or minus twice the IF frequency

Receiver Performance Image Response

Receiver Performance Image Response Images can only be reduced by improving the selectivity in the receiver front-end, BEFORE the 1st mixer. Pre-selector.

Receiver Performance Image Response Image reduction made easier when the image frequency is as far as possible from the desired frequency. Use as high an IF frequency as possible. Use a local oscillator frequency above the desired frequency. Superheterodyne.

Receiver Performance Selectivity The ability to select the desired signal & reject all others. Determined by receiver’s ENTIRE filter chain. Filters at RF frequency. Filters at IF frequency. Filters at AF frequency.

Receiver Performance Selectivity Receiver filters. Band pass filter (pre-selector). At input to RF pre-amp. Reduces interference from strong out-of-band signals. Reduces interference from image response.

Receiver Performance Selectivity Receiver filters. Roofing filter. Normally located at the input of the 1st IF amplifier, right after the 1st mixer. Typically VHF (70 MHz is common). Sharp crystal filter wider than bandwidth of widest signal to be received. Reduces IMD from strong signals outside of the filter passband.

Receiver Performance Selectivity Receiver filters. IF filters. In final IF stage. Crystal or mechanical resonator. Selectable for different operating modes. 2.4 kHz to 3.0 kHz for SSB. 500 Hz or less for CW. 300 Hz to 500 Hz for RTTY or most digital modes. Typically use soundcard software with 3.0 kHz filter. Being replaced by DSP filters.

Receiver Performance Selectivity Receiver filters. AF filters. Primarily external DSP filters. Can be narrower than IF filters. Adaptive filters can reduce noise, add notches, etc.

Receiver Performance Dynamic Range Blocking Dynamic Range. As input signal level is increased, a point is reached where output signal no longer increases linearly. Effects of poor blocking dynamic range. Gain compression or blocking. Desensitization. Nearby signal puts receiver into gain compression, reducing the apparent signal strength of desired signal. Cross-modulation.

Receiver Performance Dynamic Range Blocking Dynamic Range. Blocking dynamic range is difference between minimum discernible signal (MDS) & level where 1 dB of gain compression occurs.

Receiver Performance Dynamic Range Intercept Points. Point at which 2 equal strength signals will mix to produce an IMD product of the same strength. Example: If a pair of 40 dBm signals produce a 3rd-order IMD signal with a strength of 40 dBm, then the receiver has a 3rd-order intercept point of 40 dBm.

Receiver Performance Dynamic Range Intercept Points.

Receiver Performance Dynamic Range Intercept Points. IP2 = 2 x PA – PIM IP3 = (3 x PA – PIM3) / 2 The larger IP2 or IP3, the better the receiver linearity. Intermodulation distortion dynamic range measures the ability of a receiver to avoid generating IMD products. IMD DR3 = 0.667 x (IP3 – MDS)

Receiver Performance Dynamic Range

Receiver Performance Phase Noise. Problem became apparent when receivers got better (lower noise floor). Caused by phase jitter in PLL or DDS oscillator. Increasing noise level as you tune close to a strong signal. Noise can interfere with reception of a weak signal close to the strong one.

Receiver Performance Capture Effect. FM receivers behave differently than AM/SSB/CW receivers in the presence of QRM. AM/SSB/CW reception of an S9 signal seriously degraded by an S2 interfering signal. If 2 or more FM signals are on the same frequency, only the strongest one is demodulated. Capture effect. Not really a receiver issue. 3 dB stronger or so.

Receiver Performance Dynamic Range Intermodulation (IMD). Caused by non-linear circuits or devices. 3rd order IMD response extremely important. 3rd order subtractive products are near the desired frequency. fIMD3 = 2 x f1 – f2 or fIMD3 = 2 x f2 – f1 Roofing filters help improve IMD. Help eliminate strong in-band signals near desired signal. Will NOT help if interfering signal is within the filter passband. NOT needed for direct conversion (SDR) receivers.

E4C07 -- What does the MDS of a receiver represent? The meter display sensitivity The minimum discernible signal The multiplex distortion stability The maximum detectable spectrum

E4C05 -- What does a value of -174 dBm/Hz represent with regard to the noise floor of a receiver? The minimum detectable signal as a function of receive frequency The theoretical noise at the input of a perfect receiver at room temperature The noise figure of a 1 Hz bandwidth receiver The galactic noise contribution to minimum detectable signal

E4C15 -- What is usually the primary source of noise that can be heard from an HF receiver with an antenna connected? Detector noise Induction motor noise Receiver front-end noise Atmospheric noise

E4C06 -- A CW receiver with the AGC off has an equivalent input noise power density of -174 dBm/Hz. What would be the level of an unmodulated carrier input to this receiver that would yield an audio output SNR of 0 dB in a 400 Hz noise bandwidth? 174 dBm -164 dBm -155 dBm -148 dBm

E4C04 -- What is the definition of the noise figure of a receiver? The ratio of atmospheric noise to phase noise The noise bandwidth in Hertz compared to the theoretical bandwidth of a resistive network The ratio of thermal noise to atmospheric noise The ratio in dB of the noise generated by the receiver compared to the theoretical minimum noise

E6E05 -- Which of the following noise figure values is typical of a low-noise UHF preamplifier? 2 dB -10 dB 44 dBm -20 dBm

E4D09 -- What is the purpose of the preselector in a communications receiver? To store often-used frequencies To provide a range of AGC time constants To increase rejection of unwanted signals To allow selection of the optimum RF amplifier device

E4C02 -- Which of the following portions of a receiver can be effective in eliminating image signal interference? A front-end filter or pre-selector A narrow IF filter A notch filter A properly adjusted product detector

E4C09 -- Which of the following choices is a good reason for selecting a high frequency for the design of the IF in a conventional HF or VHF communications receiver? Fewer components in the receiver Reduced drift Easier for front-end circuitry to eliminate image responses Improved receiver noise figure

E4C14 – What transmit frequency might generate an image response signal in a receiver tuned to 14.300 MHz and which uses a 455 kHz IF frequency? 13.845 MHz 14.755 MHz 14.445 MHz 15.210 MHz Two Possible LO Frequencies: 13.845 MHz which generates a 455 KHz IF from: 13.390 MHz and 14.300 MHz Or 14.755 MHz which generates a 455 KHz IF from: 14.300 MHz and 15.210 MHz

E4C10 -- Which of the following is a desirable amount of selectivity for an amateur RTTY HF receiver? 100 Hz 300 Hz 6000 Hz 2400 Hz

E4C11 -- Which of the following is a desirable amount of selectivity for an amateur SSB phone receiver? 1 kHz 2.4 kHz 4.2 kHz 4.8 kHz

E4C12 -- What is an undesirable effect of using too wide a filter bandwidth in the IF section of a receiver? Output-offset overshoot Filter ringing Thermal-noise distortion Undesired signals may be heard

E4C13 -- How does a narrow-band roofing filter affect receiver performance? It improves sensitivity by reducing front end noise It improves intelligibility by using low Q circuitry to reduce ringing It improves dynamic range by attenuating strong signals near the receive frequency All of these choices are correct

E4C17 – Which of the following has the largest effect on an SDR receiver’s linearity? CPU register width in bits Anti-aliasing input filter bandwidth RAM speed used for data storage Analog-to-digital converter sample width in bits

E4C16 – Which of the following is caused by missing codes in an SDR receiver’s analog-to-digital converter? Distortion Overload Loss of sensitivity Excess output level

KILL E4C08 -- How might lowering the noise figure affect receiver performance? It would reduce the signal to noise ratio It would improve weak signal sensitivity It would reduce bandwidth It would increase bandwidth

E4C08 – An SDR receiver is overloaded when input signals exceed what level? One-half the maximum sample rate One-half the maximum sampling buffer size The maximum count values of the analog-to-digital converter The reference voltage of the analog-to-digital converter

E4D12 -- What is the term for the reduction in receiver sensitivity caused by a strong signal near the received frequency? Desensitization Quieting Cross-modulation interference Squelch gain rollback

E4D13 -- Which of the following can cause receiver desensitization? Audio gain adjusted too low Strong adjacent-channel signals Audio bias adjusted too high Squelch gain misadjusted

E4D01 -- What is meant by the blocking dynamic range of a receiver? The difference in dB between the noise floor and the level of an incoming signal which will cause 1 dB of gain compression The minimum difference in dB between the levels of two FM signals which will cause one signal to block the other The difference in dB between the noise floor and the third order intercept point The minimum difference in dB between two signals which produce third order intermodulation products greater than the noise floor 

E4D14 -- Which of the following is a way to reduce the likelihood of receiver desensitization? Decrease the RF bandwidth of the receiver Raise the receiver IF frequency Increase the receiver front end gain Switch from fast AGC to slow AGC

E4D11 -- Why are third-order intermodulation products created within a receiver of particular interest compared to other products? The third-order product of two signals which are in the band of interest is also likely to be within the band The third-order intercept is much higher than other orders Third-order products are an indication of poor image rejection Third-order intermodulation produces three products for every input signal within the band of interest

E4D05 -- What transmitter frequencies would cause an intermodulation-product signal in a receiver tuned to 146.70 MHz when a nearby station transmits on 146.52 MHz? 146.34 MHz and 146.61 MHz 146.88 MHz and 146.34 MHz 146.10 MHz and 147.30 MHz 173.35 MHz and 139.40 MHz Calculate the difference between each answer and the transmit frequency and add/subtract to the transmit frequency to see if comes up to the receiver frequency

E4D10 -- What does a third-order intercept level of 40 dBm mean with respect to receiver performance? Signals less than 40 dBm will not generate audible third-order intermodulation products The receiver can tolerate signals up to 40 dB above the noise floor without producing third-order intermodulation products A pair of 40 dBm signals will theoretically generate a third-order intermodulation product with the same level as the input signals A pair of 1 mW input signals will produce a third-order intermodulation product which is 40 dB stronger than the input signal

E4D02 -- Which of the following describes two problems caused by poor dynamic range in a communications receiver? Cross-modulation of the desired signal and desensitization from strong adjacent signals Oscillator instability requiring frequent retuning and loss of ability to recover the opposite sideband Cross-modulation of the desired signal and insufficient audio power to operate the speaker Oscillator instability and severe audio distortion of all but the strongest received signals

E4C01 -- What is an effect of excessive phase noise in the local oscillator section of a receiver? It limits the receiver’s ability to receive strong signals It reduces receiver sensitivity It decreases receiver third-order intermodulation distortion dynamic range It can cause strong signals on nearby frequencies to interfere with reception of weak signals

E4C03 -- What is the term for the blocking of one FM phone signal by another, stronger FM phone signal? Desensitization Cross-modulation interference Capture effect Frequency discrimination

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.

Interference and Noise 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.

Interference and Noise 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.

Interference and Noise Atmospheric Static Static noise can occur without a thunderstorm. Rain static. Snow static. Wind static.

Interference and Noise AC Line Noise Man-made noise caused by electric arc. Electric motors. Light dimmers. Neon signs. Defective doorbell or doorbell transformer.

Interference and Noise AC Line Noise Install “brute force” AC line filter in series with motor power leads.

Interference and Noise Locating Noise and Interference Sources Interference from inside building usually conducted through AC power wiring. Inside your house. Outside your house.

Interference and Noise 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.

Interference and Noise Locating Noise and Interference Sources Interference from outside building usually picked up by antenna or transmission line. Use “fox hunting” techniques to locate source.

Interference and Noise 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.

Interference and Noise 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.

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

Interference and Noise 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.

Interference and Noise Automotive Noise Vehicular System Noise 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.

Interference and Noise Automotive Noise Vehicular System Noise 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.

Interference and Noise 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.

Interference and Noise 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.

Interference and Noise 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.

E4D08 -- What causes intermodulation in an electronic circuit? Too little gain Lack of neutralization Nonlinear circuits or devices Positive feedback

E4D06 -- What is the term for unwanted signals generated by the mixing of two or more signals? Amplifier desensitization Neutralization Adjacent channel interference Intermodulation interference

E4D07 -- Which describes the most significant effect of an off-frequency signal when it is causing cross-modulation interference to a desired signal? A large increase in background noise A reduction in apparent signal strength The desired signal can no longer be heard The off-frequency unwanted signal is heard in addition to the desired signal

E4D03 -- How can intermodulation interference between two repeaters occur? When the repeaters are in close proximity and the signals cause feedback in the final amplifier of one or both transmitters When the repeaters are in close proximity and the signals mix in the final amplifier of one or both transmitters When the signals from the transmitters are reflected out of phase from airplanes passing overhead 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 band-pass filter in the feed line between the transmitter and receiver A properly terminated circulator at the output of the transmitter A Class C final amplifier A Class D final amplifier

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? The broadcast station is transmitting an over-modulated signal Nearby corroded metal joints are mixing and re-radiating the broadcast signals You are receiving sky wave signals from a distant station Your station receiver IF amplifier stage is defective

E4E06 -- What is a major cause of atmospheric static? Solar radio frequency emissions Thunderstorms Geomagnetic storms Meteor showers

E4E13 -- What might be the cause of a loud roaring or buzzing AC line interference that comes and goes at intervals? Arcing contacts in a thermostatically controlled device A defective doorbell or doorbell transformer inside a nearby residence A malfunctioning illuminated advertising display All of these choices are correct

E4E05 -- How can noise from an electric motor be suppressed? By installing a high pass filter in series with the motor’s power leads By installing a brute-force AC-line filter in series with the motor leads By installing a bypass capacitor in series with the motor leads By using a ground-fault current interrupter in the circuit used to power the motor

KILL E6D16 -- What is one reason for using ferrite toroids rather than powdered-iron toroids in an inductor? Ferrite toroids generally have lower initial permeabilities Ferrite toroids generally have better temperature stability Ferrite toroids generally require fewer turns to produce a given inductance value Ferrite toroids are easier to use with surface mount technology

E6D16 -- What is the common name for a capacitor connected across a transformer secondary that is used to absorb transient voltage spikes? Clipper capacitor Trimmer capacitor Feedback capacitor Snubber capacitor

E4E07 -- How can you determine if line noise interference is being generated within your home? By checking the power line voltage with a time domain reflectometer By observing the AC power line waveform with an oscilloscope By turning off the AC power line main circuit breaker and listening on a battery operated radio 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 common-mode signal at the frequency of the radio transmitter An electrical-sparking signal A differential-mode signal at the AC power line frequency Harmonics of the AC power line frequency

E4E15 – Which of the following can cause shielded cables to radiate or receive interference? Lower inductance ground connections at both ends of the shield Common mode currents on the shield and conductors Use of braided shielding material Tying all ground connections to a common point resulting in differential mode currents in the shield

E4E16 – What current flows equally on all conductors of an unshielded multi-conductor cable? Differential mode current Common-mode current Reactive current only Return current

E4E14 – What is one type of electrical interference that might be caused by the operation of a nearby personal computer? A loud AC hum in the audio output of your station receiver A clicking noise at intervals of a few seconds The appearance of unstable modulated or unmodulated signals at specific frequencies A whining type of noise that continually pulses off and on

E4E10 -- What is a common characteristic of interference caused by a touch controlled electrical device? 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 The interfering signal may drift slowly across the HF spectrum The interfering signal can be several kHz in width and usually repeats at regular intervals across a HF band All of these choices are correct

E4E04 -- How can conducted and radiated noise caused by an automobile alternator be suppressed? By installing filter capacitors in series with the DC power lead and by installing a blocking capacitor in the field lead By installing a noise suppression resistor and a blocking capacitor in both leads 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 By connecting the radio's power leads directly to the battery and by installing coaxial capacitors in line with the alternator leads

E4E01 -- Which of the following types of receiver noise can often be reduced by use of a receiver noise blanker? Ignition noise Broadband white noise Heterodyne interference All of these choices are correct

E4E03 -- Which of the following signals might a receiver noise blanker be able to remove from desired signals? Signals which are constant at all IF levels Signals which appear across a wide bandwidth Signals which appear at one IF but not another Signals which have a sharply peaked frequency distribution

E4E09 -- What undesirable effect can occur when using an IF noise blanker? Received audio in the speech range might have an echo effect The audio frequency bandwidth of the received signal might be compressed Nearby signals may appear to be excessively wide even if they meet emission standards FM signals can no longer be demodulated

E4E02 -- Which of the following types of receiver noise can often be reduced with a DSP noise filter? Broadband white noise Ignition noise Power line noise All of these choices are correct

E4E12 -- What is one disadvantage of using some types of automatic DSP notch-filters when attempting to copy CW signals? The DSP filter can remove the desired signal at the same time as it removes interfering signals Any nearby signal passing through the DSP system will overwhelm the desired signal Received CW signals will appear to be modulated at the DSP clock frequency Ringing in the DSP filter will completely remove the spaces between the CW characters

Questions?