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69886Re: [softrock40] Measuring toroids inductance

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  • Russ Ramirez
    Nov 10, 2012
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      I'm sure the vast majority of people who have used the microcontroller-based LC meters will attest that given a rated off the shelf inductor or a wound coil of any type specified beforehand to be xx.xx nano/microhenries, their LC meters have been quite accurate. Indeed, if you wind a given toroid that calculations show should be 7.23 uH for the core used, the LC meters will display something within a few 10ths or so of 7.23 uH. I am an EE and well versed in the models we use, but have found it hard to argue with experience and successful outcomes :-) For most of the HF frequencies there is enough slop that it usually doesn't matter. UHF/SHF is another matter entirely.


      On Sat, Nov 10, 2012 at 8:07 AM, Jack Smith <Jack.Smith@...> wrote:

      Simple PIC-based instruments measure inductance and capacitance at a rather low frequency compared with ham frequencies - in the 100-700 KHz range.

      However, an inductance value measured at say 500 KHz may or may not have a similar inductance at 5 or 25 MHz.

      Many factors enter in measured inductance versus frequency. Some are:

      1. Does the core material permeability vary with frequency? (Air, no; powdered iron, very little; ferrite material, permeability can change a great deal or a small amount with frequency depending on the particular mix.)

      2. Changes in current distribution - the winding current changes location to some degree with frequency due to skin effect and proximity effect, and as the current distribution changes, so does the inductance.

      3. Distributed capacitance - all inductors have distributed capacitance to one degree or another and as the test frequency approaches the self-resonance frequency of the inductor, the measured inductance will change, becoming very large, then zero at the SRF and negative above the SRF.

      Whether any or all of these factors are important cannot be answered in general abstract case; rather it depends on the details.

      As a rough statement, however, for inductors wound on powdered iron toroid cores and of typical values used in amateur radio construction and at frequencies in the 1-30 MHz range, a PIC-based instrument that measures inductance in the few hundred KHz range will produce useful results, with an error in the few percent range.

      I've written a detailed review of the AADE PIC-based L/C meter and discussed these factors in detail, as well as provided many measurement comparisons at

      Jack K8ZOA

      On 11/10/2012 7:57 AM, Malti wrote:

      With all due respect, there are scores of similar pic based circuits around.
      What I need is a pic based, but the coil measured under a high RF frequency.
      That is the only way to obtain very accurate readings, especially for us, at RF !
      Most use audio or slightly higher frequency, which is not enough  !


      On 10 November 2012 11:59, John Rabson <john.rabson@...> wrote:

      Or try this:

      "the kit from G4HUP available from http://g4hup.com/LCM/LCMeter.htm which is only LC but excellent for measuring and matching caps including SM parts and winding coils for HF/VHF

      John G4SWX"

      On 10 Nov 2012, at 11:27CET, pauldebono@... wrote:


      A few years ago, I came across a Russian inductance meter kit.
      Mnay designers claim to be the best one around for accurancy.

      Anyone has the details please ?
      Many of the popular meters around are dubious about accuracy, because inductance is not measured at RF, but anything but RF !


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