Krharris

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Sr. Principal Enginner

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Krharris

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  • 10.25.2007
  • Outdoors-only LCD malfunction puzzles portable-product designers
  • The ultra-low leakage (pA) silicon diode FJT-1100, made by Fairchild, comes in a glass, axial lead package. It is painted black, and the data sheet forbids scratching the paint (for good reason). I used it as a detector in an AGC circuit. A similarly strange item is ultra-high resistance resistors (over 1000 meg) made by Victoreen and packaged in glass tubing. They advise handling them by the axial leads, to avoid getting fingerprints on them, which will shunt them out of tolerance! I've seen this actually happen.
  • 08.14.2017
  • The weed-eater circuit
  • I was responsible for evaluating applicants for technician positions at a research lab. I made a test with ten questions. I don't remember all of them (from the late 70s), but I asked for resistor color code, inverting op-amp gain, four resistor transistor bias, and logic output of a circuit with a few gates. It weeded out well over half of the candidates. The one we hired was an ex-Navy technician.
  • 07.27.2017
  • Vertical antenna capacitance
  • I have read Kraus's book "Antennas" copyrighted 1950. It is the most readable and useful book on antennas I know of, with the possible exception of Tom Milligan's "Modern Antenna Design". Both of them have a lot of practical design information.
  • 01.31.2017
  • If it smells fake, it probably is
  • In the summer of 2015 I was compelled to write the editor of a generally well-respected technical publication regarding an article they had published. The problem wasn't that it was a 'pitch' but that it was simply good-sounding pseudo-science that was being published as factual. I don't mind articles that hype a product, if the product is real and does what the article says it does. Even if it is OLD, it might serve a need, or provoke a thought.
  • 01.03.2017
  • Be careful what you name your company
  • I can't help but roll my eyes at: L. E. D. Corp. My first thought is that LED Corp is an intentional acronym. I hate 'cutesy', no matter where it is. I've also noticed that every new medicine advertised on TV has a name with X, J, Z, or V (or more than one of them) in its name. How cutesy!
  • 12.09.2016
  • Electronic products from hell
  • Speaking of stuff from hell, how about the link above 'A tale of three multimeters' which seems to be broken?
  • 09.23.2016
  • MesoGlue will not replace solder
  • I too have noticed, even in technical publications, a tendency to trumpet "This NEW technology is EARTH-SHATTERING" I usually mutter "B-S" under my breath. If even a few percent of the EARTH-SHATTERING innovations fulfilled their promises, the earth would be only dust by now.
  • 07.13.2016
  • Despite Tesla accidents, autonomous vehicles are closer than they appear
  • We can't even build a car that doesn't injure people with its airbags, or accelerate unexpectedly and uncontrollably. Why should we expect self-driving cars to be any better? Of course, the brain of a self-driving car will be connected to the internet, where it can be easily hacked... Those stupid enough to do this deserve the resulting wrecks. But what about the rest of us who know better?
  • 03.24.2016
  • The mother of all LCR meters
  • cmq0 - I think the proximity effect you mention, and the distributed capacitance mentioned in the handbook are the same. It just occurred to me that with such a large inductance, core losses might be a strong contributor. My previous work was with air core designs.
  • 03.24.2016
  • The mother of all LCR meters
  • Since the skin depth of copper is 0.08 inch at 1 kHz, and 12 AWG wire is that diameter, and a 0.45 H inductor will have MANY turns, I 'm pretty sure that skin depth can't cause the difference of 42 ohms at dc and 90 ohms at 1 kHz. If the frequency were 100 kHz, though, the skin depth becomes 0.008 inch, the diameter of 32 AWG wire and a more likely culprit. Distributed capacitance is a much more likely problem. With the large number of turns, that capacitance will be large. This affects the apparent L, R, and Q, as described in the 'Radiotron Designer's Handbook' published by RCA in 1954 (on page 451). Assuming the measured L is correct, the apparent resistance is given by R(1+Co/C)^2 where R is the actual resistance, Co is the distributed coil resistance, and C is the external capacitance needed to resonate L at the frequency of interest. If Co is 25 nF, that is enough to account for the observed resistance. I first came across this while working on a loop antenna at 125 kHz to activate tire pressure monitors. So this was known before I was born...