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Banana Skins – August 2022 (#394-396)

394. GHz radar pulses can interfere with motor cars

Because of their mobility, vehicles will be placed in many different kinds of Electromagnetic environment. From driving next to transformers and high voltage power lines operating at 50 or 60Hz to driving next to airports where the approaching and landing radars operate at 1.2 to 1.4GHz and 2.7 to 3.1GHz.

Manufacturers of vehicles found some isolated cases where vehicles in the proximity of airports and military bases were affected by the radiated fields from radar systems. The high fields from the radar interfered with the normal operation of critical systems in the vehicle. These systems included braking controls and airbag deployment. Given the importance of the problem the management of vehicle manufacturers applied pressure on the EMC departments to come up with a test plan to check components (what the auto industry often call electronic sub-assemblies, or ESAs – Editor) for electromagnetic immunity to these pulses. 

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VSWR and its Effects on Power Amplifiers

Voltage Standing Wave Ratio results from an impedance mismatch between a source (an amplifier) and a load (test application). This mismatch can influence the performance of the source.

Both Ford Motor Company and General Motors Worldwide introduced sections in their immunity standards for component testing to radar pulses. Generating 600V/m pulses at these frequencies requires the use of high power amplifiers and/or very high gain antennas. In the process of developing antennas optimised to meet these requirements, several issues with the test were discovered. While the test can be done it requires very expensive equipment that is not easily afforded by many small component manufacturers and test houses. As a result of some of the anomalies seen during the testing of the antenna prototypes Ford have made some changes to the tests described in their document.

(Taken from: “High Field Radar Frequency Pulse Test for Automotive Components”, V Roderiguez et al, EMC Society of Australia Newsletter, Issue 35, December 2006.)

395. Telecomm globalisation and related interference issues

Some uniformity does exist in the requirements of the POTS (plain-old-telephone-system), at least in how the equipment works. Regulatory standards that the phone equipment must comply with vary from country to country, however. No one knows this fact better than the designers at Silicon Labs. Many years ago, they set out to design a modem that would comply with every standard in the world. Thus, they created the Isomodem line of chips. 

The name of one system block of all modems, the DAA (direct-access arrangement), provides a clue to the challenges that designers face. The chips must ultimately interface with the real-world twisted-pair wiring, which can encounter lightning strikes and line-cross events. A line cross occurs when the electric power that is running on the same utility poles as the telephone lines breaks and falls across the phone line. In some regions of the United States those utility poles carry 440V-ac power, and peak voltage is more than 600V. European lines, on the other hand, directly distribute 240V (actually 230V rms, 240V only in the UK – Editor). Nevertheless, the standards for the line-cross event differ all over the world. 

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In the United States, FCC Part 68 specifies the design limits and testing and requires surge testing at 1500V. In Europe, European standard EN 55024 specifies the limits and does testing at 1000V. Real-world conditions are even more demanding: A line-cross event may generate only a few hundred volts on a phone line, but a lightning strike can far more voltage, and the rise time of that event will be short. Designers at Silicon Labs have seen field voltages of 4500V.

(Taken from “Globalisation and Analog”, by Paul Rako, EDN Global Report 3, December 2006.)

396. Some power quality issues for products marketed worldwide

To compete in the global market, today’s analog ICs must address a wide range of application and vo9ltage requirements,” says Doug Bailey, vice-president of marketing for Power Integrations. “For example, we know that Japan’s ac main can be as low as 90V power, whereas Europe uses 240V (actually 230V rms, 240V only in the UK – Editor). At first blush, this information seems like enough to design a power supply that will operate worldwide. The reality is more difficult. In India, the power grid is unreliable, forcing many big electricity consumers to use private generators during outages.

When the power goes down, and the generators switch in, numerous line spikes occur. When the power grid comes back up, everyone’s using generators. The power grid is unloaded, so the voltage can overshoot and ring for several minutes. The resulting surges can go as high as 400V. Products have to be able to handle these extremes, so our application circuits must cover ultra-wide ranges of voltage and help ensure that our chips withstand the spikes.

(Taken from “Globalisation and Analog”, by Paul Rako, EDN Global Report 3, December 2006.) 

The regular “Banana Skins” column was published in the EMC Journal, starting in January 1998. Alan E. Hutley, a prominent member of the electronics community, distinguished publisher of the EMC Journal, founder of the EMCIA EMC Industry Association and the EMCUK Exhibition & Conference, has graciously given his permission for In Compliance to republish this reader-favorite column. The Banana Skin columns were compiled by Keith Armstrong, of Cherry Clough Consultants Ltd, from items he found in various publications, and anecdotes and links sent in by the many fans of the column. All of the EMC Journal columns are available at: https://www.emcstandards.co.uk/emi-stories, indexed both by application and type of EM disturbance, and new ones have recently begun being added. Keith has also given his permission for these stories to be shared through In Compliance as a service to the worldwide EMC community. We are proud to carry on the tradition of sharing Banana Skins for the purpose of promoting education for EMI/EMC engineers.

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