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Q meter

Discussion in 'Homebrew and Kit Projects' started by KP4SX, Nov 30, 2019.

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  1. W1BR

    W1BR Ham Member QRZ Page

    Wow, neat! How much is the kit Bill? I want one
     
  2. KP4SX

    KP4SX XML Subscriber QRZ Page

    Pete, see the link in the first post. Mine was $30-something and the case was another 12.
    Ming is also a great source for all sizes of Litz wire which he sells on ebay.
     
  3. KP4SX

    KP4SX XML Subscriber QRZ Page

    You are lucky! I once got into a batch of FT68-? that were giving 400-500 in the BCB range. Was never able to repeat that stunt.
     
  4. KP4SX

    KP4SX XML Subscriber QRZ Page

    Correction. Those 'magic' ones were FT50-61 now that my memory has kicked in. You wouldn't expect more than 200-300 out of one on a good day.
    Another war story...I had a bag with some cores on the shelf next to my old CRT monitor. They sat there for months. When I went to use them I checked and although the Al was correct the Q wasn't much better than an oatmeal box. I didn't realize up to that point that they could be affected so much by a magnetic field. I forget if they were iron or ferrite but I suspect ferrite.
    So, in the interest of science I played with them and a magnet. You can really kill a core with magnetism! Another reason to have a good checker/tester.
     
  5. N1OOQ

    N1OOQ Ham Member QRZ Page

    Hmm, interesting. I wonder if it could be useful?

    A few months ago, I saw an old RSGB article about tuning a VFO by driving current through a winding on some paired toroids. Tried it, nada. I was putting 3 amps through the darn winding, no change in freq!
     
  6. KP4SX

    KP4SX XML Subscriber QRZ Page

    That sounds like heresy -haha!
    Things was, the Al value didn't seem to change significantly although the Q did. So I dunno how that could be useful for tuning.
    But hey, this is how we learn things!
     
  7. N1OOQ

    N1OOQ Ham Member QRZ Page

    Yah, one generally doesn't want lower Q...

    I'm always looking for interesting ways of tuning a VFO, especially non-mechanical ones.
     
  8. W1BR

    W1BR Ham Member QRZ Page

    I had some engineering samples for current-controlled inductors that I was going to try in a phase locked loop system. It has been done in the past. Oddest example of magnetic control in an inductor transformer has to be handed to GE for their Colorama tuning system used in some of their higher end late 1930's consoles and tombstone radios. The AGC controlled a saturable core that controlled red and green pilot lamps... tuning to center changed the dial color.

    Pete
     
    N1OOQ likes this.
  9. N1OOQ

    N1OOQ Ham Member QRZ Page

    Yah, the RGSB article pointed to a couple of older articles where the authors had done similar things. So I know it can be done. The key might be saturability. I tried it with powder toroids, which are harder to saturate, and haven't gotten back to it.
     
  10. VK2TIL

    VK2TIL Ham Member QRZ Page

    The Fair-Rite catalogue (17th ed., available for download) describes the effects of a DC current on ferrite permeability; both u' and u" can be substantially reduced.

    As a crude experiment, I measured Rs (related to u") and Xs (related to u') of a winding on #43 material; two data sets, one under the influence of an external magnet and the other without that magnet, were taken.

    The magnet was simply the end of a magnetic pickup tool applied to the side of the toroid; this is simpler than applying DC to the winding and, since this is just a demonstration, adequate for the purpose..

    [​IMG]


    There was certainly a change;the values at 10 MHz were;

    Rs without magnet 1045 ohms; Rs with magnet 273 ohms.

    Xs without magnet 998 ohms; Xs with magnet 581 ohms.

    #43 is not the material for tuned circuits but the effect of DC current/magnetism on permeability is illustrated.
     
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