LF: Re: DSP-filter for aural CW

["Roelof Bakker" <roelof@ndb.demon.nl>]

Hello Dick,

PA0LQ's filter is now in wide spread use amongst NDB afficiados in favour of 
DSP filters.
By increasing the 10 nF capacitors to 27 nF and "stagger tuning" it has been 
possible to reduce the bandwidth from 30 Hz to 6 Hz with steep slopes.
At present I am using two of these filters in cascade, 12 Hz and 6 Hz wide 
at a centre frequency of 500 Hz.
The fixed tuning resistors have been replaced by multiturn trimmers of 1 K.
Aligning section 1 and 3 for maximum signal at 495 Hz and section 2 and 4 at 
505 Hz, yields a 3 dB bandwidth of 10 Hz. This is wide enough to copy 20 WPM 
morse code.
Best regards,

Roelof Bakker, pa0rdt