In the early 1920s the signals from the then ubiquitous spark transmitters sounded like a cross between an angry bumblebee and a canary being given an enema. The noise was 120dB over S9 since all the transmissions were below 1500kc (Hertz was in the canary renting business then.) Who could tell if there was interference? However, the telephone wires were on poles parallel to the power mains, and the arcing and sparking in the power distribution system caused interference on the phones.

When the radio engineers cleaned up their act – invented the vacuum tube and started transmitting continuous wave emissions – two things happened. The signals became narrow band, about 24 cps, and since transmitter frequencies were no longer limited by the rotation rate of electric motors, frequencies became higher – up to, gasp, 10 or 15MHz. (Hertz had finally been recognized for developing the spaghetti recipe used in Marconi’s trattoria.) Radio interference was born, followed by letters to D.C. because power line noise was interfering with Amos and Andy.

Military RFI was born because the telephone system to the tail gunner was wrapped into a harness with the power wiring to the tail of the B29. The radio man used to pipe Tokyo Rose into the audio system and the poor tail gunner couldn’t hear the music from the radio, so they called it Radio Frequency Interference. When the military got involved, they had to write specifications, of course.

The problem was that rotating machines, rectifiers (866s) and fluorescent lights caused the power lines to broadcast hash and other undigestible stuff. The Army’s MIL-I-11748 and the Navy’s MIL-I-16910 used open area test sites because they didn’t want to get involved with volumetric site attenuation.

The Army Air Force, however, figured all their problems were inside aluminum airplanes so they opted for screen rooms in which to make the measurements described in MIL-I-6181. To their surprise and delight they found that there was no radio noise and it didn’t rain or snow inside their screen rooms. The spooks, not to be outdone, made a few copies of FED-STD-222 which they kept locked up in safes so nobody could make the required measurements. Because they were worried about the magnetic field around Kleinschmidt teletype machines, the all steel-sheet shielded enclosure was born.

About this time the Institute of Radio Engineers Radio Interference group formed the dB Society. To cut out the inter-service rivalry, MIL-STD-461, 462 and 463 were substituted for the old specs. Immediately the Army, Navy and Air Force promulgated Notes A through Z which reestablished their EMC turf. Everyone was staying warm and dry until the Dumont Television Network invented television interference, TVI. The wide band interference from the Trash-80s caused a pile up of more letters to the FCC because folks couldn’t watch Uncle Miltie.

So the FCC wrote FCC Part 15 which said you must go out into a corn field. For 30 years perfectly good interference measurements had been made in shielded rooms – thank you very much. The Europeans finally got into the act and decided all those thousands of worst case peak measurements were no good, so for CISPR-22 you needed quasi peak detectors – which, by the way, were available only in equipment made in Europe.

Now here we are in Hawaii, sipping pineapple coladas and waiting with bated breath for the western arc of the Pacific Rim to dump their xerox copies of European specks and write their own – guess rice paddies are next.