Posted by
Geoffrey Mackenzie-Kennedy-2 on
Nov 13, 2004; 10:22am
URL: http://elecraft.85.s1.nabble.com/Talking-filter-Bandwidths-tp371577p371587.html
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" <
[hidden email]>
To: <
[hidden email]>
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
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