Eric, KE6US wrote: I don't have your experience or background, Ron, but the L-meter is measuring inductance indirectly and ignoring the presence of distributed capacitance. Maybe it isn't as negligible at the frequency of the meter as you think.
But in the end, it doesn't really matter. The real test is how a particular toroid reacts in the circuit it was intended for. If adjusting the turns spacing changes circuit resonance, then...it changes circuit resonance. That's the result we would have been looking for. Hi. -------------------------- I'm fond of saying that the only dumb question is the question not asked, so your question is an excellent one, Eric. As for lots of experience, for me that's too often just an opportunity to remember more things incorrectly. About your question, my L-meter evaluates inductance using a low-frequency square wave at about 60 kHz that goes to a differentiator consisting of a 200 ohm resistor in series with the unknown inductance. The waveform at the junction of the resistor and inductor is a series of spikes at the frequency of the input square wave. The spikes decay at a rate proportional to the time constant of the resistor and inductor. This decay rate is converted into a voltage in a simple logic circuit. The ARRL Handbook has featured this circuit in a number of editions. It's a simple and surprisingly accurate meter, depending upon the quality of the inductors used to calibrate it. The way the circuit works means that any significant capacity in parallel with the inductor would tend to cancel the effect of the inductor, and make the inductance value displayed read lower than it really was, not higher. Again, at the bench I tested that conclusion by adding capacitors in parallel with the inductor. Sure 'nuf, adding capacitance decreased the reading. Recall that squeezing the turns together raised the test inductor value read on the meter from 3.1 to 3.3 uH. Now I added fixed capacitors across the inductor to simulate added distributed capacitance caused by squeezing them together. Adding 10 pf of capacitance across the inductor had zero effect on the reading. Adding 33 pf across the inductor *lowered* the reading by 0.1 uH. We're dealing with a very small toroid in this test whose inter-turn capacitance isn't going to be as much as 2 or 3 pf when squeezed together. So I'm confident that the added capacitance by squeezing the turns together is not what is causing my L-meter to show increased inductance. If anything, the capacitance would tend to cause the L-meter to show lower inductance. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
