I have modified my Yaesu FT-817, replacing the stock 2.2KHz Murata ceramic filter with a Collins 2.3KHz mechanical filter.I did this so I could use a better filter on SSB but still allowing me to use the Yaesu YF-122C CW filter in the optional filter slot.
The better noise shape and punchy selectivity is immediately noticeable when you turn the radio on after fitting the mechanical filter. According to the report I read on the W4RT site, the filter is also advantageous in transmit, effectively adding a few dB to the signal without touching the radio’s output power, although I haven’t proved that for myself.
I did all I could to ensure no internal interference was created when using fly leads to get from the 817′s main PCB to the Collins filter, such as keeping them as short as possible and creating some screening from copper wire strands and insulation tape, and it seems to have worked – with the antenna unplugged I am not picking up any unwanted noise caused by RF pick-up from within the chassis.
Care has to be taken to do this mod, as there are lots of tiny SMDs right next to where you need to remove/replace the filter. This mod is reversible simply by de-soldering the fly leads and refitting the Murata CFJ455K ceramic filter. For those who prefer something a little more polished, W4RT do a One Board Filter (OBF) solution which is a little daughter board that houses both the SSB and CW filters – although some delicate work is needed with this solution too. If you are not sure, ask your dealer if they fit – W4RT electronics themselves do offer a fitting service.