K4DPK VFO Stabilizer

Discussion in 'Radio Circuits, Repair & Performance' started by DV1UBY, Aug 14, 2011.

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  1. DV1UBY

    DV1UBY Ham Member QRZ Page

    Hi guys,

    Any thoughts about K4DPK's VFO Stabilizer? I have my Yaesu FT-707 here and it is more often sent to the technician. Anyone here knows where t obtain K4DPK's VFO Stabilizer? I'm from Manila, PHL.

    Also, I tried to check the net and can't find further info about K4DPK's VFO Stabilizer.

    Thanks. :)
  2. KB4QAA

    KB4QAA XML Subscriber QRZ Page

  3. K0CRX

    K0CRX Ham Member QRZ Page


    You might try Cumbria in England. Here's a link http://www.cumbriadesigns.co.uk/x-lock.htm.

    I have an ongoing project using their X Lock with a Heathkit HG-10. I have experimented enough to know that the X Lock is working fine. The current problem is that the added varicap pulls the oscillator tank too far to compensate with a normal alignment. I plan to experiment with different varicaps, but, the bottom line is the X Lock works fine in stabilizing the VFO.
  4. DV1UBY

    DV1UBY Ham Member QRZ Page

    Is there anyone can help me find the K4DPK's VFO Stabilizer for my Yaesu FT-707? Any contacts with K4DPK? Until now he's not answering my email. Please help thanks :D
  5. DV1UBY

    DV1UBY Ham Member QRZ Page

    Hi K0CRX,

    Is it (the X Lock) good for my Yaesu FT-707? Does it really fix the drifting issue? Or just a replacement for the IC of the VFO (just like the Japanese produced MSM9520RS Replacement Module)? :D
  6. K0CRX

    K0CRX Ham Member QRZ Page


    The X-Lock is a 'huff and puff' circuit (I think that's the correct terminology) that will provide a varying DC output as the input frequency changes (drifts). That DC output, then, biases a varactor, which, when connected to the oscillator tank, provides a corrective capacitance to the tank, thus, bringing the oscillator back on freq. I only understand the function from a high level and can not explain how the detailed circuitry works.

    I do know that my own experimentation using an X-Lock with a Heathkit HG-10 showed very effective freq stability correction. I could monitor the oscillator freq with a freq counter and, when it changed by as little a one cycle, the X-Lock would bring it back. The problem I encountered, and have not yet solved, is that the introduction of the varactor into the oscillator tank upset the oscillator L/C ratio to the point where mere recalibration would not bring it back to the original frequency range. The X-Lock folks recommend using an LED as the varactor. I have only experimented with one LED. I'm hoping that I can find another LED or a real varactor with a capacitance value that does not upset the oscillator tank.

    Sadly, that project has been back-burnered and is in a box on the shelf. Hopefully, I'll get back to it this winter. I operate mostly vintage (vacuum tube) radios and want to put some very vintage SSB stuff on the air and don't want to be wandering up and down the band!! :eek:

    As to your FT-707, I'm not familiar with that radio, but, if the oscillator is of conventional design with an L/C tank, I would think the X-Lock would be a good candidate.

    BTW, the X-Lock folks are friendly and helpful, too!
    Last edited: Aug 21, 2011
  7. KO6WB

    KO6WB Premium Subscriber QRZ Page

    For the X Lock you might want to try a 1N914 diode instead of the LED. It has smaller excurtions in capacitance verses voltage and it just might cure your problem.
    Hope that helps
  8. K0CRX

    K0CRX Ham Member QRZ Page

    Thanks, Gary. I appreciate the tip!!
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