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.
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
Circuit diagram. Chebyshev 8 pole ladder type crystal filter
