You can put in an op amp analog filter for very small outlay of cash.
I can remember building my first audio filter in the dark ages around 1973. Used toroids probably surplus from the phone company to build filters, and vacuum tubes to amplify the audio signals. Worked pretty good!!! Far far easier today.
From: BITX20@groups.io <BITX20@groups.io> on behalf of _Dave_ K0MBT <davesters@...>
Sent: Friday, August 16, 2019 7:08 AM
Subject: Re: [BITX20] Narrow filter for CW #ubitxcw
Yes I was hoping to steal someones design and spend less than 10 dollars.
Have to agree that adding a 300 dollar filter to a radio that I bought used for 45 dollars is not going to happen.