I recently ordered a lovely 500 Hz mechanical filter to use for CW on my FT-897 and FT-817—the YF-122C. I was baffled for much of this week because I could not make it work in the FT-817. If I changed the OP FILTER setting to CW it was as though there was no filter installed at all. If I set it to SSB the filter was engaged but of course the offset was wrong. It’s not helpful at all unless I want to do CW at 1250 Hz.
The difficulty turned out to be this cheeky little menu option: NAR. This is one of the settings that you access by pressing the F button briefly then rotating the SEL knob. When a narrow CW filter is installed it must be engaged by pressing the C button, which places the little triangle to the left. This function key lets you easily toggle the filter in and out, which is very useful when you’re scouting around for QSOs.
Yaesu does not bother to point out this setting in the part of the manual that describes installing the filter. I am writing this small post in the hope that it will save someone else some trouble.