Morning Deni, The bandwidth of a filter (in whatever form) has always been taken to mean the bandwidth between the upper and lower 3db points of the filter's attenuation vs frequency response, the 0db point being at the frequency of least attenuation in the pass band. One hopes that the passband ripple is much much less than 3db !! Other bandwidths are used, but the dbs of attenuation must always be specified. If the attenuation is not specified, then the 3db bandwidth is used.
The bandwidth at 6db attenuation is used together with the bandwidth at 60db attenuation to determine the filter's shape factor, a number >1. Very often the bandwidth at 80db of attenuation is used instead of that at 60db attenuation, but the dbs of attenuation must always be specified. There are good reasons for using the 6db figure, but I won't confuse the issue. 73 Geoff GM4ESD (near Cupar, Fife). ----- Original Message ----- From: "Deni" <[EMAIL PROTECTED]> To: <elecraft@mailman.qth.net> Sent: Saturday, November 13, 2004 7:45 AM Subject: [Elecraft] Talking filter Bandwidths I have recently replaced my CW Xtal Fiter set and done a realignment using Spectrogram. I'm now attempting to measure my selected filter bandwidths and using the -6dB points, is this incorrect ? Is -3dB now the preferred or accepted points for BW measurement specs? Why is there some apparent confusion here, any thoughts? 73, Deni K21188 F5VJC / GM3SKN _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
