Question of the Week - Answer 220606https://learnemc.com/qotw-220606

EMC Question of the Week: June 6, 2022 The graph in this figure plots impedance as a function of distance from electric and magnetic dipole sources. Plots similar to this appear in countless EMC texts and articles. What type of impedance is this?...

Question of the Week - Answer 231113https://learnemc.com/qotw-231113

EMC Question of the Week: November 13, 2023 In an equipment rack, each piece of equipment should usually be grounded at a single point in the rack the front of the rack the back of the rack the front and back of the rack Answer The best answer is “d.”...

Question of the Week - Answer 201109https://learnemc.com/qotw-201109

EMC Question of the Week: November 9, 2020 Assuming the dielectric materials are the same, which transmission line would have the longest propagation delay? microstrip trace pair stripline trace pair unshielded parallel wires shielded twisted wire pair...

Question of the Week - Answer 220815https://learnemc.com/qotw-220815

EMC Question of the Week: August 15, 2022 To determine the characteristic impedance of a 1-km length of cable, use a high-frequency RLC meter to measure the input resistance inductance capacitance both (b) and (c) Answer The best answer is “a.” When a...

Question of the Week - Answer 230109https://learnemc.com/qotw-230109

EMC Question of the Week: January 9, 2023 Slowing the transition time of a 10 MHz trapezoidal waveform from 1 ns to 5 ns reduces the maximum amplitude of harmonics above 320 MHz by 0 dB 5 dB 7 dB 14 dB Answer The best answer is “d.” Harmonics fall off...

Question of the Week - Answer 230731https://learnemc.com/qotw-230731

EMC Question of the Week: July 31, 2023 Two planes in a circuit board form a patch antenna producing radiated emissions at 1.5 GHz. The circuit board sits on a 1-meter wooden table, and the emissions are measured in a semi-anechoic chamber at a 1-meter...

Question of the Week - Answer 230306https://learnemc.com/qotw-230306

EMC Question of the Week: March 6, 2023 A voltage source drives a quarter-wave monopole that resonates at 300 MHz. The radiation resistance is 36 Ω. If a ferrite core (R = 80 Ω at 300 MHz) is placed on the monopole, the radiated emissions from the...

Question of the Week - Answer 221114https://learnemc.com/qotw-221114

EMC Question of the Week: November 14, 2022 Suppose the separation distance between two microstrip traces is increased, reducing the mutual capacitance between them by a factor of two. In this case, the mutual inductance between the two circuits will...

Question of the Week - Answer 221031https://learnemc.com/qotw-221031

EMC Question of the Week: October 31, 2022 The current distribution on a half-ounce copper plane below a microstrip trace at 100 MHz is mostly concentrated under the trace as indicated in the figure. At 1 GHz, we would expect the current distribution...

Question of the Week - Answer 250818https://learnemc.com/qotw-250818

EMC Question of the Week: August 18, 2025 Which of the following phrases best describes a requirement for an EMC ground? conductor of relatively large extent small relative to a wavelength return current path connection to the earth Answer The best...

Question of the Week - Answer 200525https://learnemc.com/qotw-200525

EMC Question of the Week: May 25, 2020 A ribbon cable is used to convey a single-ended 1-Mbps 3.3-volt digital signal between two circuit boards. A good estimate for the worst-case emissions around 100 MHz (as measured in an FCC Class B radiated...

Question of the Week - Answer 201228https://learnemc.com/qotw-201228

EMC Question of the Week: December 28, 2020 The amplitude of the 5th harmonic of a 3.3-volt, 10-MHz clock signal with a 1-ns transition time is approximately 600 mV 300 mV 30 mV 60 μV Answer The correct answer is “b.” There are several ways to quickly...

Question of the Week - Answer 220516https://learnemc.com/qotw-220516

EMC Question of the Week: May 16, 2022 A coaxial cable carrying a 100 Mbps digital signal connects a system controller in a metal box to a sensor board in a plastic box. To minimize the common-mode current on the cable shield, it's important to have a...

Question of the Week - Answer 221226https://learnemc.com/qotw-221226

EMC Question of the Week: December 26, 2022 Generally, a ferrite bead on a circuit board should never be in series with a signal trace an I/O trace a power trace a ground trace Answer The best answer is “d.” Traces labeled "ground" are usually...

Question of the Week - Answer 250901https://learnemc.com/qotw-250901

EMC Question of the Week: September 1, 2025 Which of these currents is primarily responsible for radiated emissions from cables? odd mode even mode differential mode common mode Answer The best answer is “d.” It is the common-mode current on cables...

Question of the Week - Answer 240401https://learnemc.com/qotw-240401

EMC Question of the Day: April 1, 2024 Faraday cages were first developed in what century? 9th 19th 20th 21st Answer The correct answer is “a.” In 891, Alfred the Great, King of Wessex, had a problem. Waves of Danish invaders kept his armies busy far...

Question of the Week - Answer 201116https://learnemc.com/qotw-201116

EMC Question of the Week: November 16, 2020 A 100-Mbps single-ended signal propagates from its source to the edge of a circuit board on a microstrip trace. At the board edge, it transitions to a ribbon cable where the signal current flows on one wire...

Question of the Week - Answer 220228https://learnemc.com/qotw-220228

EMC Question of the Week: February 28, 2022 For the standard electrical outlets shown in the figure, the terminals that electrically connect to the earth outside the building are labeled HOT NEUTRAL GROUND Both NEUTRAL and GROUND Answer The best answer...

Question of the Week - Answer 221212https://learnemc.com/qotw-221212

EMC Question of the Week: December 12, 2022 Conducted emissions testing of a 12-volt device reveals that the noise on the power wire (VBATT+) is 12 dB over the limit. The noise on the power return wire (VBATT-) is 12 dB below the limit. This product...

Question of the Week - Answer 211227https://learnemc.com/qotw-211227

EMC Question of the Week: December 27, 2021 In the digital oscilloscope display shown in the figure, what is the frequency of the second peak in the FFT? 1 kHz 2 kHz 3 kHz 4 kHz Answer The correct answer is “c.” The time-domain waveform (blue trace) is...

Question of the Week - Answer 240429https://learnemc.com/qotw-240429

EMC Question of the Week: April 29, 2024 A stripline trace in a circuit board is 0.2 mm wide and 0.25 mm from the planes above and below it. The dielectric is FR-4 (εr = 4.3). What is the ratio of the electric field strength to the magnetic field...

Question of the Week - Answer 220307https://learnemc.com/qotw-220307

EMC Question of the Week: March 7, 2022 The duty cycle of a PWM waveform increases from 50% to 90%. The amplitude, frequency and transition times stay the same. In the frequency domain, what happens to the amplitude of the first harmonic? increases...

Question of the Week - Answer 220131https://learnemc.com/qotw-220131

EMC Question of the Week: January 31, 2022 The quasi-peak amplitude in a radiated emissions measurement is 46 dB(μV/m). The quasi-peak limit at that frequency is 40 dB(μV/m). The measured value is over the limit by 6 dB(μV/m) 12 dB(μV/m) 20 dB(μV/m) 40...

Question of the Week - Answer 201214https://learnemc.com/qotw-201214

EMC Question of the Week: December 14, 2020 Reducing the video bandwidth on an EMI test receiver or spectrum analyzer impacts the measurement in a manner similar to reducing the resolution bandwidth reducing the signal bandwidth adding an attenuator to...

Question of the Week - Answer 250113https://learnemc.com/qotw-250113

EMC Question of the Week: January 13, 2025 Driven with the same ideal voltage source, between 10 MHz and 10 GHz, which of these antennas produces the highest radiated emissions at its resonant frequency? 20-cm matched 377-Ω parallel wires (2-cm...

Question of the Week - Answer 221017https://learnemc.com/qotw-221017

EMC Question of the Week: October 17, 2022 Faraday's Law says that the sum of the voltages around a closed loop is always equal to zero loop current times resistance loop current times inductance ∂/∂t [magnetic flux passing through loop] Answer The...

Question of the Week - Answer 250331https://learnemc.com/qotw-250331

EMC Question of the Week: March 31, 2025 Which acronym below was commonly used to describe electromagnetic interference decades ago? RMS ELF EMB RFI Answer The best answer is “d.” Long before the acronym EMI entered the lexicon, the term used to...

Question of the Week - Answer 250106https://learnemc.com/qotw-250106

EMC Question of the Week: January 6, 2025 When designing for EMC compliance, it is important to realize that the EMC ground is generally a path for returning currents to their source a conducting body of relatively large extent non-existent above 100...

Question of the Week - Answer 220926https://learnemc.com/qotw-220926

EMC Question of the Week: September 26, 2022 Above the cut-off frequency, the insertion loss of an ideal low-pass pi-filter increases at a rate of 20 dB/decade 40 dB/decade 60 dB/decade 6 dB/octave Answer The best answer is “c.” A pi-filter is a...

Question of the Week - Answer 230220https://learnemc.com/qotw-230220

EMC Question of the Week: February 20, 2023 At high frequencies, which field quantity just above a metal surface has a magnitude approximately equal to the magnitude of the surface current density? magnetic field tangential electric field normal...

Question of the Week - Answer 240506https://learnemc.com/qotw-240506

EMC Question of the Week: May 6, 2024 Suppose the radiated emissions from a product are proportional to the common-mode current on its power cable. Suppose the common-mode current on the cable is proportional to the time-rate-of-change of the voltage...

Question of the Week - Answer 200706https://learnemc.com/qotw-200706

EMC Question of the Week: July 6, 2020 A single-ended 10-MHz digital clock propagating on a circuit board (75-Ω microstrip line) passes through a connector where it transitions to a 100-Ω twisted wire pair. If the peak-to-peak differential voltage on...

Question of the Week - Answer 210315https://learnemc.com/qotw-210315

EMC Question of the Week: March 15, 2021 For a pair of identical circuit board traces over a ground plane, the difference between differential-mode propagation and odd-mode propagation is differential-mode is undefined odd-mode is undefined a factor of...

Question of the Week - Answer 250623https://learnemc.com/qotw-250623

EMC Question of the Week: June 23, 2025 A shielded cable with twisted wire-pairs carrying high-frequency signals connects to a circuit board mounted in a plastic enclosure with no metal chassis. The circuit board has a solid copper GND/RTN plane. In...

Question of the Week - Answer 210628https://learnemc.com/qotw-210628

EMC Question of the Week: June 28, 2021 At a given frequency between 30 MHz and 1 GHz, what is the lowest common-mode current on a cable attached to a table-top product that is capable of causing an FCC or CISPR Class B radiated emissions failure? 5 A...

Question of the Week - Answer 200817https://learnemc.com/qotw-200817

EMC Question of the Week: August 17, 2020 The reason some application notes recommend returning two or more signal currents to a single common point is to give those signals the same zero-volt reference to reduce common-impedance coupling to eliminate...

Question of the Week - Answer 230619https://learnemc.com/qotw-230619

EMC Question of the Week: June 19, 2023 The two-port network illustrated in the attached figure is a low-pass filter high-pass filter band-pass filter band-stop filter Answer The best answer is “c.” The schematic in the figure shows an active band-pass...

Question of the Week - Answer 220207https://learnemc.com/qotw-220207

EMC Question of the Week: February 7, 2022 A 2-MHz synchronous buck converter is used to convert 12 VDC to 3.3 VDC. The high-side and low-side switches are internal to the converter IC. The inductor is external. The current with the highest time rate...

Question of the Week - Answer 230821https://learnemc.com/qotw-230821

EMC Question of the Week: August 21, 2023 Which two-terminal transient protection device has a V-I curve similar to the one shown in the figure? Avalanche diode TVS diode Varistor Thyristor Answer The best answer is “d.” Two-terminal thyristors have a...

Question of the Week - Answer 210726https://learnemc.com/qotw-210726

EMC Question of the Week: July 26, 2021 For a trapezoidal digital signal waveform, the "knee frequency" above which harmonics begin decreasing by 40 dB/decade is 1/(πtr), where tr is the transition time 1/πT, where T is the period (10πtr)/T, where tr...

Question of the Week - Answer 230807https://learnemc.com/qotw-230807

EMC Question of the Week: August 7, 2023 An isolated differential source drives an unbalanced wire pair. One wire in the pair has a 1-mm diameter and the other wire has a 2-mm diameter. If the source supplies 10 mA of current, what is the common-mode...

Question of the Week - Answer 241202https://learnemc.com/qotw-241202

EMC Question of the Week: December 2, 2024 A 2-Ω, 100-MHz clock source drives 4 CMOS inputs on a circuit board over a distance of about 5 cm. The trace impedance is about 75 Ω. Which terminating resistor(s) configuration shown in the figure is...

Question of the Week - Answer 250203https://learnemc.com/qotw-250203

EMC Question of the Week: February 3, 2025 A current filament in free space carries a sinusoidal current, Ic. The intrinsic impedance of free space is η0. The free-space wavelength is λ. If the length of the current filament is ℓ, which equation for...

Question of the Week - Answer 240318https://learnemc.com/qotw-240318

EMC Question of the Week: March 18, 2024 A 24-VDC component has a two-wire power cord and fails to meet its conducted emissions requirement at 360 kHz (the third harmonic of the buck converter on the power input). Two LISNs are employed in the test...

Question of the Week - Answer 250224https://learnemc.com/qotw-250224

EMC Question of the Week: February 24, 2025 Which radiated emissions specification is the most stringent at 100 MHz? FCC Part 15 Class B CISPR 32 Class B MIL-STD-461 RE102 CISPR 25 (automotive) Class 5 Answer The best answer is “c” although a good...

Question of the Week - Answer 200316https://learnemc.com/qotw-200316

EMC Question of the Week: March 16, 2020 The third harmonic of a continuous clock signal shows up as a narrow band peak in a conducted emissions measurement. How does the value measured with an average detector compare to the value measured with a peak...

Question of the Week - Answer 210517https://learnemc.com/qotw-210517

EMC Question of the Week: May 17, 2021 The connection inductance of an 0603 SMT decoupling capacitor that is well-mounted to a printed circuit board 2 or 3 layers above the power/ground plane pair is typically a couple nanohenries hundred picohenries...

Question of the Week - Answer 221024https://learnemc.com/qotw-221024

EMC Question of the Week: October 24, 2022 The inductance of a tightly wound coil of wire with N turns is approximately proportional to N N2 wire radius coil radius Answer The best answer is “b.” The inductance of a coil of wire is approximately...

Question of the Week - Answer 201019https://learnemc.com/qotw-201019

EMC Question of the Week: October 19, 2020 When driving a CMOS load (capacitive termination), overshoot and ringing on an otherwise good digital waveform is a clear indication that the _______ has not been properly controlled. connection inductance...

Question of the Week - Answer 250324https://learnemc.com/qotw-250324

EMC Question of the Week: March 24, 2025 Which of these two-port networks is fully characterized by its S-parameters? (a) (b) (a) and (b) (a) and (b) and (c) Answer The best answer is “a.” If the S-parameters were determined by driving each of these...