The Smell of Molten Projects in the Morning

Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.

The New Hotness

  • Monthly Science: 60 kHz Preamp Resonator Bandwidth

    Putting a small capacitor in series with the tuning fork resonator pulls the series resonant frequency upward and reduces the amplitude:

    60 kHz Quartz TF Resonator - CX variations
    60 kHz Quartz TF Resonator – CX variations

    So something around 10 pF, net of stray capacitance and suchlike, should suffice. Plunk a small twiddlecap on the preamp board and tune for best picture:

    LF Crystal Tester - resonator protection
    LF Crystal Tester – resonator protection

    Using the DDS generator as a manual signal source with 1.0 Hz step size shows the resonator tightens up the preamp’s response quite nicely:

    60 kHz Preamp - Bandwidth - 1 Hz steps
    60 kHz Preamp – Bandwidth – 1 Hz steps

    I’m not convinced the preamp will have filter skirts that low farther away from the peak, but it’ll do for a start.

    Zoom in on the peak with 0.1 Hz steps:

    60 kHz Preamp - Bandwidth - 100 mHz steps
    60 kHz Preamp – Bandwidth – 100 mHz steps

    The bandwidth looks like 0.6 Hz, centered just slightly above 60.000 kHz, which should be fine for a first pass.

    I’m tickled: all the hardware & firmware fell neatly into place to make those graphs possible!

    Next step: install it in the attic and see whether the filter cuts back the RF clutter enough to stabilize the SDR’s AGC gain.