John Dunn

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Consultant

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John Dunn

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  • 08.14.2017
  • 6 Comment(s)
The weed-eater circuit
  • 07.27.2017
  • 2 Comment(s)
Vertical antenna capacitance
  • 06.27.2017
PIN diode drive
  • 06.15.2017
  • 3 Comment(s)
MIL-STD-704 simulation on the cheap
  • 06.12.2017
  • 3 Comment(s)
Embedded resistance measurement
  • 06.02.2017
  • 10 Comment(s)
Limitless gain
  • 04.26.2017
Cheap sweep
  • 04.04.2017
  • 3 Comment(s)
Slippin' and a slidin'
  • 06.02.2017
  • Limitless gain
  • I have heard that if you want to make an oscillator, try to make an amplifier and if you want to make an amplifier, try to make an oscillator. Whichever is your goal, you will end up with the other. The circuit I built was on vectorboard with no wires any longer than a small fraction of an inch. There were no long loops of wire or anything else like that. The SPICE model shows "Vcc" but I'm sure I put rail bypasses there such as a 0.1 µF ceramic capacitor in parallel with a tantalum electrolytic of maybe 10 µF. That in parallel with the output impedance of the Hewlett-Packard bench supply was quite adequate. I barely gave it a thought. It was just good practice to do those things and I had lots of gain with no sign of any instability..
  • 06.15.2017
  • MIL-STD-704 simulation on the cheap
  • Actually, I'm not the originator of this thing. It was originated, I think, back around 1978 by a co-worker of whom I have long since lost track, a man named Dan Barsanti. When I first tried to use it, there were some operating problems so I had to make some modifications into the configuration shown here.
  • 06.02.2017
  • Limitless gain
  • I tried some time ago to learn how to use LTSpice, but the user interface defied my best efforts to comprehend. Then one day, I attended a multi-hour seminar about LTSpice which was presented by the author. I've forgotten the fellow's name, but never mind. The goal seemed to be to show all of the amazing and wonderful things that could be done with LTSpice. As each topic was presented, it was like seeing and hearing click-click-click-click-swish- click-click and then my staring at whatever result was being presented without my having been able to follow the step-by-step procedure that had gotten things to where they were. This happened over and over again for the entire session. That night, armed with fresh memories of the seminar results, I tried again to use LTSpice but just like before, I could NOT make the user interface work. I was totally, completely, impotently unable to make ANYTHING useful take place. Since then, I've totally ignored LTSpice in favor of using Multisim which gives me no such trouble.
  • 06.02.2017
  • Limitless gain
  • We used a small benchtop supply then sold by HP. I never gave it a second thought, but there was no problem with that.
  • 02.25.2017
  • Doubled-up MOSFETs
  • That should be "marks a MOSFET", not "makes a MOSFET". I must have had a single event upset in my cranium.
  • 02.12.2017
  • Inverted mode switches
  • That's some find, Steve! I'm beginning to think if someone reported a new use for the wheel, you could find the wheel's introductory article written by its inventor. :)
  • 02.12.2017
  • Inverted mode switches
  • I never looked into any analysis of why this works. I only read about it and then used it.
  • 12.26.2016
  • Underwater Navy drones: Can electronics deter illegal seizures and technology theft?
  • Fifty years ago when I was working for a military electronics company, I saw these silver packets about the size of a thick slice of bread that were placed inside of sensitive pieces of ALQ-xxxx equipment and which were designed to go incendiary if tampered with. The idea was to reduce EVERYTHING to an utterly useless, carbonized lump.
  • 12.20.2016
  • The Picard Loop
  • The loops are indeed placed at the store doorways. Clerks at the cash registers are supposed to remove the magnetic tags from purchased items, but I once bought a tie clip where the clerk forgot to do so. The alarm sounded as I was trying to leave the store so I had to present my receipt to the security guard. I was apologetically told that the clerk would be reprimanded Also, yes, false positives are a problem, especially from steel shopping carts. It's a very long story, but Knogo Corporation once tried to make magnetic tags with unidirectional hysteresis loops to differentiate their tags from other magnetic objects. There was a big spread in the newspaper Newsday about that. They called their item "Superstrips" but so far as I know, the idea never came to fruition.