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crystal filter

Crystal filters are bandpass filters of high quality and enormous slope. They are monolithically constructed and consist of several multiple resonators.

Several quartz crystals are mounted on a quartz disk. The cascading of the resonators increases the already high slope steepness of the quartz filters. The quality factor of quartz filters is between 10,000 and 100,000.

Resonance curve of a crystal filter

Resonance curve of a crystal filter

A commercially available crystal filter with a center frequency of 70.2 MHz and a bandwidth of 19 kHz will be used as an example. At 70.16 MHz, i.e. 40 kHz from the resonant frequency, this crystal filter already has an attenuation of more than 80 dB. Spurious waves that are 40 kHz or more from the center frequency have no effect on the transmitted frequency because of the high attenuation.

Similar in design to the crystal filter is the ceramic filter, which has a ceramic resonator instead of quartz plates. However, these RF filters have higher attenuations and lower Q.

Englisch: crystal filter
Updated at: 25.07.2012
#Words: 154
Links: cascading, quality factor (Q), crystal (XTAL), filter, frequency (f)
Translations: DE

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