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Banana Skins – August 2020 (#286-290)

286.  Electronic organ manufacturer fined for EMC non-compliance

The Enforcement Bureau of the Federal Communications Commission (FCC) has fined a Dutch company for importing and marketing in the United States electronic organs which radiated emissions in excess of U.S. limits. The company, Johannus Orgelbouw b.v. of the Netherlands, was fined US$7000 and ordered to submit to the FCC for the next two years verification records for each model of organ which it imports into the U.S.

The matter of the emitting digital electronic organ was brought to the attention of the Enforcement Bureau in early 2003 by a competitor who claimed that other organ companies were suffering competitive harm because the company, by not complying with FCC regulations, was able to produce products less expensively. In a subsequent investigation by FCC agents, the company acknowledged that it had imported and marketed at least one model of organ that did not comply with FCC emissions limits, resulting in the Commission’s action.

(From “FCC Fines Importer of Non-Compliant Electronic Organs”, Conformity, News Breaks, February 2004, pp 42-43.)

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287.  False alarm in the Bahamas, caused by inadequate immunity of field meter

Once upon a time, when the Bahamas telephone toll center transactions were only $175,000 US per day — and EMC engineers made a great deal less — our facilities safety manager was attending to his appointed rounds with his brand-new, brand name RF field intensity meter in hand. He wanted to make sure that the electric fields within the facility were less than the allowed maximum of 10mw/ (194 V/m). After all, our company didn’t want to accidentally cook anyone that worked there. It wouldn’t look good come time to renew their management contract.

Much to the safety engineer’s surprise, the fields being presented by the video display units (VDUs) at the operator consoles were way above the maximums. A quick calculation disclosed that the measured field intensities were in excess of 300 V/m. Did he call anyone? Did he ask how that was possible? Of course not! Being a good safetyman, with genuine concern for the workforce, he immediately shut down the toll center. Then, he called to report his findings. Then, his boss called corporate headquarters and they called my boss and also those of six other EMC facilities that we had scattered around the world. Then seven EMC engineers, myself included, immediately reported to the Bahamas to solve this serious problem. At $175,000 per day there was a lot of incentive to get there quickly.

We were prompt, but still didn’t arrive at the same time. But when we did, we found that the first EMC engineer on the scene had already discovered that the brand-new, brand name RF field intensity meter was susceptible to the 15kHz VDU raster sweep frequency, and the toll center was back on-line. Of course, this required an appropriate celebration at a little place nearby… but that’s a different story!

(“A really short ‘vacation’ in the Bahamas”, Ron Brewer, IEEE EMC Society Newsletter, Spring 2004, ‘Chapter Chatter’ section, page 8.)

Numbers 288 – 290 are taken from the Appendix to MIL-STD-464A dated 18 March 1997. (MIL-STD-464A is entitled “Department of Defense — Interface Standard —Electromagnetic Environmental Effects — Requirements for Systems”.)

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288.  From MIL-STD-464A A.5.2 “Intra-system electromagnetic compatibility (EMC)”

When appropriate controls are implemented in system design, such as hardening, EMI requirements on subsystems and equipment, and good grounding and bonding practices, there are relatively few intra-system EMC problems found. Most problems that are found involve antenna-connected transmitters and receivers. Receiver performance has been degraded by broadband thermal noise, harmonics, and spurious outputs coupled antenna-to-antenna from transmitters. Microprocessor clock harmonics radiating from system cabling and degrading receivers have been another common problem. Electromagnetic fields radiated from onboard antennas have affected a variety of subsystems on platforms.

Typical non-antenna related problems have been transients coupled cable-to-cable from unsuppressed inductive devices and power frequencies coupling into audio interphone and video signal lines. Problems due to cable-to-cable coupling of steady state noise and direct conduction of transient or steady state noise are usually identified and resolved early in the development of a system. Generation of broadband EMI on ships from electrical arcing has been a common source of degradation of antenna-connected receivers and must be controlled. Sources of the arcing have been brush noise from electrical machinery and induced voltages and currents between metallic items from antenna transmissions. Intermittent contact of the metallic items due to wind or ship motion is a contributor.

289.  From MIL-STD-464A A.5.3 “External RF EME”

(EME means electromagnetic environment, used in this document to mean only the radiated environment)

High-powered shipboard radars have caused interference to satellite terminals located on other ships, resulting in loss of lock on the satellite and complete disruption of communication. The interference disables the satellite terminal for up to 15 minutes, which is the time required to re-establish the satellite link. Standoff distances of up 20 nautical miles between ships are required to avoid the problem.

A weapon system suffered severe interference due to insufficient channel selectivity in the receiver’s front end. Energy originating from electronic warfare systems and another nearby “sister” channelized weapon system (operating on a different channel but within the same passband) coupled into the victim receiver and was “processed,” severely degrading target detection and tracking capability. Installation of an electronically tuned filter immediately after the antenna countered the off-channel interference problem by: 1) eliminating receiver front-end amplifier saturation and 2) reducing overload of the system processor with extraneous in-band signals.

An aircraft lost anti-skid braking capability upon landing due to RF fields from a ground radar changing the weight-on-wheels signal from a proximity switch. The signal indicated to the aircraft that it was airborne and disabled the anti-skid system. An aircraft experienced uncommanded flight control movement when flying in the vicinity of a high power transmitter, resulting in the loss of the aircraft. If the mission profile of the aircraft and the anticipated operational EME had been more accurately considered, this catastrophe could have been averted.

Aircraft systems have experienced
self-test failures and fluctuations in cockpit instruments, such as engine speed indicators and fuel flow indicators, caused by sweeping shipboard radars during flight-deck operations. These false indications and test failures have resulted in numerous unnecessary pre-flight aborts.

Aircraft on approach to carrier decks have experienced interference from shipboard radars. One such problem involved the triggering of false “Wheels Warning” lights, indicating that the landing gear is not down and locked. A wave-off or preflight abort could occur due to this EMI induced condition.

Aircrews have reported severe interference to communications with and among flight deck crew members. UHF emissions in the flight deck environment caused interference severe enough that crews could not hear each other for aircrew coordination. This problem poses a serious hazard to personnel with the potential for damage to, or loss of, the aircraft and aircrew during carrier flight deck operations.

290.  From MIL-STD-464A A.5.4 “Lightning”

The effects of lightning can cause physical damage to personnel and equipment. In one of numerous documented lightning incidences, lightning appeared to enter a Navy aircraft nose, travel down the right side, and exit on top of the right vertical tail. The pilot suffered from flash blindness for 10-15 seconds. Upon regaining his vision, the pilot noticed all cockpit electrical power was gone. After another 15 seconds had elapsed, all cockpit electrical power returned on its own, with no cockpit indications of any equipment malfunction.

In another case, lightning attached to the nose pitot tube, inducing transients that damaged all 28 volt DC systems. The pilot, disoriented, broke out of a cloud bank at 2000 feet above the ground, at 600 knots and a 45 degree dive. Nearly all cockpit instruments were dysfunctional – compass, gyrohorizon, and so forth. A secondary effect occurred but was not uncovered for several months. The lightning current path that carried the direct effects lightning current did what it was supposed to do, but the path was not inspected on landing.

Over 800 man-hours were expended to correct electrical (28 volt DC) problems but no effort went into inspecting for direct effects damage to ensure the lightning protection system was intact. The rigid coax from the front of the radome to the bulkhead had elongated and nearly torn away from its attachment point at the bulkhead due to magnetic forces involved. This damage reduced the effectiveness of the designed lightning protection. Another secondary effect was the magnetization of all ferrous material which caused severe compass errors. The entire aircraft had to be degaussed.

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