Electronic Design

Bob's Mailbox

Hi Bob: I've been an avid fan of yours for many years, and I'm writing now to plumb the depths of your arcane knowledge. We've got a design that needs a little bit of insulation, and I told the engineer to use fish paper to do the job. She asked me a question that's got me stumped: "What's the origin of the term fish paper (and how did it come to be associated with vulcanized fiber)?" A search on the Internet left me still scratching my head. Any ideas?

  • Matthew L. Severns (via e-mail)
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  • Pease: If you go to www.jjorly.com/fish_paper_die_cut.htm, it will explain about fish paper—why it has an electrical spec drawing and conforms to MIL-I-695F, and why it is rated to high temps with good electrical and mechanical characteristics. I gotta admit, it does not seem to explain the source of the name. On the other hand, www.smallparts.com/ products/descriptions/fshp.cfm says that fish paper is made out of cotton rags. Maybe it's thus named because it smells like fish. Does anyone know the origin of the name?

Dear Bob: I want to raise a concern about the gaining popularity of using spread-spectrum techniques in switching power supplies (As in other digital computing chips... /rap) to allegedly reduce EMI. Of course, this does not really reduce the EMI. It just spreads it out so the equipment can pass the regulatory tests, which are performed using narrow-band detectors. Because a real receiver like a TV set is wideband, in practice, the interference is not reduced. (The total radiated power may actually be increased, as there is no need for shielding or good layouts. /rap)

One advertisement shows a CW interference carrier being reduced by what looks like an impressive 20 dB. But the reduction is only because the measurement is being made in a 100-Hz bandwidth. With the proliferation of wireless RF technology, I think we all need to design products that truly pass EMI requirements without resorting to tricks that exploit loopholes in the test methods. With the proliferation of switching power supplies and unfiltered lamp dimmers, AM radio has already become almost unusable.

  • Mark Kolber (via e-mail)
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  • Pease: Well, every loophole will be investigated, and if they seem to work legally and save money, people will use them. Hey, shielding is expensive! And making a good new re-layout usually takes a lot of time—and it's hard to be sure that it will work! I don't see the FCC cracking down on this in the near future. Heck, people are permitted to spray broadband noise over our power lines (and they are not even twisted pairs)! Permissiveness seems much more rampant. Regulators don't give a damn. Anything that lets you get out a product faster and cheaper is a great idea, no?

Dear Bob: I am remiss not to write sooner—been terribly busy with hurricanes, grandkids, work, etc. I just got to your column on naps (ELECTRONIC DESIGN, May 12, p. 20) and I found it to be very funny, but quite accurate. Could it be that you and I are getting a bit long in the tooth? I am now 73—the days of working with Bob Widlar, Brent Welling, Brian Hollins, and Bob Swanson are a faint, but fond, memory. (I was with you at National Semi from 1976 to 1980.)

As I have told you, I still work full-time consulting for the USAF and plan to continue to do so as long as my health will allow. But on the subject of naps, I find that going home during the lunch break and taking a 15-minute "power" nap will refresh me entirely for the remainder of the afternoon. I have no trouble working a nine-hour day (with a 45-minute lunch period). So, I totally agree with you—naps are good things. And I really enjoyed your column.

  • Jerry Robertson (via e-mail)
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  • Pease: Surprisingly, I usually get through the day without a nap during lunchtime. Not sure why. Keep up the good work!! Best regards from a kid of just 65.

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