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Re: Daughterboard won't oscillate on 40.5MHz

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  • n2pk2001
    Hi Dave, Rs=40 ohms is fairly high for the 40.5 MHz crystal but it should still work. Since it works at 56 MHz, you might first check the number of turns on
    Message 1 of 4 , Sep 1 9:20 AM
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      Hi Dave,

      Rs=40 ohms is fairly high for the 40.5 MHz
      crystal but it should still work.

      Since it works at 56 MHz, you might first
      check the number of turns on L100. If that
      is correct, then try moving them closer
      together. I am assuming they are currently
      spread fairly uniformly around the core
      perimeter.

      If that still doesn't work, then double
      check the rest of the parts.

      73,
      Paul, N2Pk
    • Dave
      Squishing the turns as close as I could get them got 40.50MHz to oscillate. My battery has discharged to about 11.5V, dropping the p-p output voltage a bit.
      Message 2 of 4 , Sep 2 8:42 AM
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        Squishing the turns as close as I could get them got 40.50MHz
        to oscillate. My battery has discharged to about 11.5V, dropping
        the p-p output voltage a bit. 56.2 is now 2.25V and 40.5 is
        about 1.8V (it takes a moment for 40.5 to reach stable p-p
        voltage).

        L100 has the correct number of 12 turns (12 passes through the
        toroid). Unsquished it measured 0.47uH and squished it measures
        0.51uH (both a bit higher than the schematic-stated 0.43uH).
        Perhaps I will try changing from 12 to 13 turns which should give
        me about 0.55uH measured unsquished, but I suppose that might kill
        the 56.2 oscillation.

        Dave, WA3OFF
      • Dave
        ... I wound 13 turns (unsquished) on another T25-6 core I had in stock and measured it at 0.54uH. With the supply now at 11.4V, 40.50 now has output of 2.3V
        Message 3 of 4 , Sep 2 9:58 AM
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          > L100 has the correct number of 12 turns (12 passes through the
          > toroid). Unsquished it measured 0.47uH and squished it measures
          > 0.51uH (both a bit higher than the schematic-stated 0.43uH).
          > Perhaps I will try changing from 12 to 13 turns which should give
          > me about 0.55uH measured unsquished, but I suppose that might kill
          > the 56.2 oscillation.

          I wound 13 turns (unsquished) on another T25-6 core I had in stock
          and measured it at 0.54uH. With the supply now at 11.4V, 40.50 now
          has output of 2.3V p-p (and comes up to that almost immediately) and
          56.2 has 2.2V p-p, so I think I'll call it ready to install.

          Thanks for the help.

          Dave, WA3OFF
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