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I have a boatload of 165.550 MHz Regency 10.7 MHz IF Crystals. I need them to resonate for 165.500 MHz. How can I shift the crystal frequency down 50 KHz without opening the 'tincan' and messing with it? Can I add a small capacitor in parallel to shift the crystal frequency down? How can I determine the value of the Cap? Likewise, is there a rule of thumb in order raise the frequency of a crystal? Is 50KC too big of a jump? Thanks Much, 73 J

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2 Answers 2

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You can add inductance in a sequence like this.

schematic

simulate this circuit – Schematic created using CircuitLab

Yes, you can also try adding capacitance in parallel.

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  • $\begingroup$ I never thought about that, but what's the influence of adding a series inductance (even assuming it having no resistive parasitics) on the Q of a such a resonator? $\endgroup$ Apr 2 at 11:31
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    $\begingroup$ to answer my comment here: the Q should stay around the same, see Glen's simulations here. Note that you'll probably not be able to pull the quartz much further than a couple parts per thousand. Nice! $\endgroup$ Apr 4 at 14:59
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    $\begingroup$ Any external component will lower Q. I would be more worried about thermal stability, especially at 160MHz. Crystals have around 50ppm for -40..+85°C range which is up to 8KHz for the whole temperature range. You can easily get a few hundred hertz when your circuit gets warmed up. I would recommend to use inductance instead of trimmer capacitor because its contact more stable. $\endgroup$
    – k1zmt
    Apr 5 at 2:44
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I assume these are 3rd or 5th overtone crystals. It is not possible to pull overtone crystals that far in frequency. You can generate one fixed frequency from another one but the effort to do that is considerable, compared to a simple crystal with the correct resonant frequency.

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