Collins mechanical filters or crystal filters for the 455 kHz SSB or CW optional filter slot are no longer available for the FT-847 from INRAD. We have exhausted our supply of adapter circuit boards with matching network for this transceiver model. Collins CW filters are also no longer available, discontinued as of 2017.
Crystal filters available for 5 different narrow bandwidths are wired-in with RG174U coax to our "C" board, as the case size of the radio will not accommodate the filter being installed directly onto the board. To install a crystal filter, we pre-wire the filter and board for you. The "C" board is plugged into the optional slot, and then the crystal filter and coaxial cables are placed elsewhere inside the case (directions with pictures provided). No soldering necessary.
The FT-847 can use either Collins filters or crystal filters in the CW slot, but crystal filters have much better shape factors than mechanical filters and will improve the selectivity of the radio. Since the crystal filters are much larger and will not fit in the sockets, they must be wired in as described above.