By John Brubaker
In the early 80s I worked for AT&T Bell Labs in their Computer Division. We were building and selling Super Mini Computers. The FCC decided to extend its EMI requirements on computers. So, after the long and difficult process, we found a local testing company to test our systems for us.
We took this monstrous thing out to the boonies and set the 4 6′ tall cabinets on the turn table. We did some preliminary test with doors open and everything looked great. So when we did the actual test, with the doors closed, at a 45 degree angle from the antenna we had this huge RF spike way up in the MHz range. When the antenna was at any other angle to the machine it was very quiet. In trying to troubleshoot the issue, one of the engineers opened the rear doors while the machine was at the 45 degree angle. The noise disappeared, close the doors and the signal blasted out. After some head scratching, we discovered that the hinged side of the rear doors left about a 1/4″ gap for entire 6′ length of the door. One of the old guys realized this gap was a perfect microwave slot antenna. We installed some conductive fillers in the gap and the noise left.
Just for grins!! The last one of these machines I designed was for the NSA. It was 24′ long and weighed 8,000 pounds. It was one of the first of the Echelon Systems listening in on your phone calls. Oh it was high for those days it had one cabinet of disk drives that gave it 2.4G of storage. AHHHH the good old days - hahahaha.
John Brubaker went to work for Bell Labs in 1981. He worked there until the early 90s. Most of his work involved opto-mechanical design. After that he started his own R&D company. He also has done some contract engineering. He worked on some fun things like a new 1.6 gal toilet, water filter connections - yes when you change you water filter with the push in tube you can blame John for that. He now works around his farm, puttering around with some solar work.