Quartz Crystal Filter Design

Some kind of introduction ...

Quartz crystals are highly selective "tuned circuits" in a filter network. The development of quartz crystals is closely linked to the development of radio, shortly after World War I. Almost one century later, it is a mass product and therefore a welcome object for homebrewing filters. The very high Q allows the realisation of very narrow bandpass filters. This website is an attempt to handle those devices.

CMOS Quartz Crystal Oscillator (5.12 MHz), the round disc is the quartz.

Selecting Quartz Crystals with "equal" properties

To get started building quartz crystal filters, it is recommended to buy a larger amount of crystals. Selecting then a few with almost similiar properties dramatically simplifies the mathematics. For this task, we use the Crystal Checker, which was developped only for exactly this task. Together with a (high resolution) frequency counter, the quartz crystals may then be grouped, according to frequency.

Hint #1 : As IF filters are usually at "low" frequencies, we suggest you use fundamental quartz crystals only. This covers the range to approx. 30 MHz.

Hint #2 : Do not touch the quartz crystals too long, as frequency will change by some Hertz.






Having done so, you may proceed to find the "inner values" aka Replacement Circuit
The Downloads below refer to the Crystal Checker.

The Manufacturing of Synthetic Quartz Crystals

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