All the following is used with permission of the author. Thanks guys.
I wanted to flatten the response curve a bit:
I poked around the coupling capacitors in the filter and tried doubling the caps without much effect so I tried to remove one to see if that made a difference. I picked the middle one for no particular reason at all and removed its shunt cap (C8).
After removing C8, the 3db bandwidth is about 175 hz rather than the 50 hz it was before. Now, when I tune in a signal, I have about 11 steps of the tune switch where I can hear the signal and about 5 steps where it is relatively loud.
I like it better this way, you may like the tighter filter.
Before removing C8:
After removing C8
(Paul Stroud AA4XX)
I went ahead and performed this crytal filter mod on my ATS3 over the weekend and really like the widened response. It’s still narrow enough for my taste while allowing me to know who’s above and below me–a real advantage for those occasions when the calling station is more than 500 Hz off frequency. I removed C8 and shorted across X2 to convert the original filter to a 3-crytal Cohn filter.
The nice thing about the mod is that all the solder points can be readily accessed without having to remove the board from the Altoids tin.