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Thread: Ts-520 Calibrator Marker Board 25 Khz., Error.

  1. #1

    Join Date
    Dec 2019
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    Kuna, Idaho
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    Default Please delete post

    No follow-up allowed to reply, I will not be posting again...not comfortable with the process.
    Last edited by Mac; Thu 2nd Jan 2020 at 20:20. Reason: Want to delete, not comfortable with the process.

  2. #2

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    Ash Fork, Arizona
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    Default

    You have come across a pretty interesting circuit. While it isn't used any more, and you can barely find a reference to the operating mode in any book or document, I still find it interesting. It's not really used any more, mostly because it's a bit unstable and there are better, easier, ways to do the same thing.

    The heart of that circuit is the Astable Multivibrator (Q2 and Q3). The multivibrator is designed to operate naturally at around 25 KHz. It doesn't divide or scale the oscillator frequency, but rather syncs to it. The crystal oscillator (Q1), running at 100 KHz, is coupled to the multivibrator via the 1N60 diode (D1). This coupling provides sync pulses for the multivibrator, which syncs to every fourth clock.

    For low divide ratios, less than 10, this works pretty well. But, as the part values drift over time, the multivibrator could easily obtain sync at a different ratio. You might think that, the natural frequency of the multivibrator would go up, with C6 decreasing, from 39 to 24 pF. But that's part of the instability. Rather than syncing to every second or third cycle, it synced to every tenth.

    The signal from multivibrator doesn't have nice clean edges. But to be rich in harmonics, the rise and fall times need to be fast. So the output transistor (Q4), in a saturated mode, is used to clean up the the multivibrator signal.

    Thanks for the interesting circuit.

    Martin, K7MEM

  3. #3

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    Dec 2019
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    Kuna, Idaho
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    Thumbs up I'm out of sync.

    Thanks for putting me straight, technically speaking, on the sync aspect. I'm old, forgetful and sometimes hopelessly, hopeless. I will yield to the correct explanation and pull the post after a reasonable time to allow users to see your response and get straight. I'm not into, unwittingly, putting out bad or incorrect information. Thanks, Mac

  4. #4

    Join Date
    Dec 2019
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    Default Attn: Moderator

    On second thought, please pull my post. My circuit description is, after thinking about that fellows (K7mem) reply, wrong; his description is correct. People who read the post may not read the reply and hence, be misinformed. Thanks, Ed "Mac" McKnight, W7LW.

  5. #5

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    Dec 2019
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    Kuna, Idaho
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    Default Kenwood ts-520 Marker board follow-up.

    I hadn’t bothered to digest Kenwood’s circuit description until now; I had just winged it, thinking I fully understood it.

    Here is the actual circuit description per the Kenwood TS-520 manual. Note in the last sentence; “Q4 amplifies the calibrator signal.” If it looks like an rf amplifier and the designers say it’s an rf amplifier, it probably is an rf amplifier. Concerning “synching,” … the deterioration in capacitance of C-6 caused the output to become 10khz pulses and increasing the capacitor to design value, slowed it up (?) to 25khz. I still see the math in it, although I could be wrong; I think they call that a caveat.

    “5.7 MARKER BOARD (X52-0005-01)
    The MARKER board holds the 100 khz crystal oscillator (Q1) and the 25 khz multivibrator (Q2 and Q3) to produce marker signals at 25 khz intervals to calibrate the TS-520. Q4 amplifies the calibrator signal.”

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