very narrow crystal filter

41 very narrow crystal filter Good filters can be expensive and a manufactured one with a band-pass characteristic as good as the circuit described here would leave you considerably lighter in the pocket. In spite of its performance, the circuit usesonly standard components and is ideally suited for applications in CW receivers. Asthe circuit diagram shows, the filter is of the normai X tel 1 ... X-1,1 4= 1 MH, X-tr.,I 1 X-1,I 2 X.tal 3 X tal4 C1 C2 C3 C4 CS Zin TT ~ 0V 18Op 180p 7-56 ) Zout 680t_ 680t, 18op T ~0p 83536 ladder configuration with standard 1 MHz crystals. However, ample proof of the performance is provided by the photograph taken on a spectrum analyser. It shows that the 6 dB pass-band is only 120 Hz, while that at 60 dB is only 400 Hz! The insertion loss of 4 dB is reasonable. Furthermore, as the tolerance of 1 MHz crystals is relatively smalt, the filter can be "repeated" very easily. N