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

  • Crystal Properties

    Spent some Quality Shop Time measuring an assortment of crystals, some data from which will make up a Circuit Cellar column.

    And the raw numbers will come in handy one of these days, so here they are…

    12 MHz Asst HC-49/U Co+Cc/2 2Cc Fs BW Rs
    ECS 1 4.85 1.47 12.000162 787.5 40.1
    ECS 2 4.50 1.42 12.000150 725.0 40.1
    ECS 3 4.70 1.42 12.000325 1100.0 50.0 Rs out of range
    HC1 4 4.34 1.11 11.999000 600.0 36.0
    HC1 5 4.24 1.06 12.000137 537.5 36.9
    Sentry 6 5.14 0.96 12.000250 625.0 31.8 many spurs
    11.0592 MHz HC-49/U
    1 4.90 1.42 11.059275 562.5 9.3
    2 4.99 1.46 11.059112 575.0 14.7
    3 4.87 1.42 11.059275 512.5 9.6
    4 4.87 1.41 11.059125 550.0 10.0
    5 4.29 1.43 11.058935 750.0 18.1
    6 4.93 1.47 11.059000 537.5 10.7
    7 4.95 1.47 11.059200 525.0 8.1
    8 5.03 1.45 11.059037 575.0 11.1
    10 MHz HC-49/U spur +150 kHz
    1 2.57 1.36 9.997888 200.0 14.2
    2 2.61 1.30 9.997738 225.0 16.7
    3 2.75 1.30 9.997788 225.0 20.0
    4 2.67 1.30 9.997750 225.0 16.1
    5 2.75 1.26 9.997725 250.0 22.7
    6 2.69 1.27 9.997788 225.0 21.0
    7 2.69 1.26 9.997825 212.5 16.5 Circuit Cellar example
    8 2.69 1.22 9.997832 212.5 18.4
    9 2.72 1.24 9.997788 250.0 23.4
    10 2.68 1.20 9.997738 225.0 18.0
    18.43 MHz HC-49/US many spurs +10 +76 kHz
    1 3.86 1.33 18.432425 1.56 24.1
    2 3.79 1.22 18.432987 1.21 10.9
    3 3.93 1.39 18.432050 2.44 46.3
    4 3.97 1.40 18.431175 1.90 27.7
    5 3.89 1.33 18.431888 2.11 32.2
    6 3.92 1.39 18.430888 1.39 16.5
    7 3.99 1.35 18.431500 1.36 11.8
    8 3.97 1.35 18.431675 2.18 38.4
    9 3.95 1.31 18.430512 1.30 10.1
    10 4.04 1.50 18.431427 1.36 11.8

    The 18.43 MHz crystals are in the short /US cans with surprisingly high stray capacitance. Their bandwidths are in kHz and all over the map, as are the series resistances. Weird. Bad crystals? Bad technique?

    Capacitance measured with that fixture.

    Frequency & bandwidth from HP8591 spectrum analyzer with a fixture similar to the K8IQY design; the bandwidths seem to come in 12.5 Hz increments despite a (very narrow) 2 kHz span. The general process is there. Resistance measured from a cermet trimpot using a multimeter good for 0.1 Ω around 10 Ω.

    Crystal Test Fixture
    Crystal Test Fixture

    Useful equations, with column headings in boldface:

    • Lead-to-can capacitance for each lead: Cc = 2Cc / 2
    • Lead-to-lead capacitance: Co = Co+Cc/2 – Cc/2
    • Circuit Q: Q = Fs/BW
    • Circuit resistance: R = Rs + 25 (assuming 4:1 transformers)
    • Reactance XL = XC at series resonance: X = Q R
    • Motional inductance: Lm = X / (2 π Fs)
    • Motional capacitance: Cm = 1 / (2 π Fs X)
    • Parallel resonance Fp = Fs √(1 + (Cm / Co))

    More equations there.

    Memo to Self: Zero the capacitance fixture before critical measurements!