Category Archives: Crystal filters 9MHz

Crystal filter 9MHz 2.7kHz

One of the most important modules in the home made HF transceiver project is the crystal filter. It is made of individual quartz crystals with matched parameters – Fser. (+/- 15Hz), Lm and Q factor > 100 000.  A large quantity of 9MHz oscillator crystals were purchased to extract only few to fit those requirements. Three type of quartz filters are used in this project – main (roofing) filter, narrow filter for SSB or CW modes and noise filter. All the filters are internally impedance matched to 50 ohm input/output circuitry and individually aligned.

img_3916  img_3917

Here is information about first – wide 2.7kHz SSB filter:

Filter type                          Chebyshev 8 pole

Center frequency             9MHz

Bandwith at -6db             2.7kHz

shape factor -6/-60db    1.75

IN/OUT impedance        50ohm

Band pass ripple              <1db

Stop band attenuation    >80db

VNA plot

9mhz-2-7khz

Circuit diagram. Chebyshev 8 pole ladder type crystal filter

xtalfil-9mhz-2-7khz

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