The place a narrow IF filter *DOES* help is when trying to copy a weak station with a very strong (local) station > 1 KHz away.
I repeat my advice that the best solution is simply to increase the gain between the receiver output and the computer so that, WITH that strong signal present, the green bar as as close as possible to 80 dB without turning red. Working 6M with three very strong neighbors running legal limit, I'm still able to decode very weak stations that I want to work.
