The stock FL-96 (455 kHz SSB: 2,8 kHz wide @ -6 dB) can be replaced with an FL-44A (2,4 kHz wide @ -6 dB) to improve adjacent-channel selectivity and sharpen Twin PBT operation. In addition, the stock FL-102 (9 MHz, AM) can be replaced with an FL-223 (9 MHz SSB: 1,9 kHz wide @ -6 dB) to provide an SSB-NARROW bandwidth setting.
Here is the filter installation procedure:
(I would suggest that you purchase an IC-781 service manual from Icom Parts for guidance, if you do not already have one. Icom Parts should also have the FL-44A).
- Remove the top and bottom case covers.
- Lay the radio upside down on a towel, with the front panel facing you.
- Using a magnetic-tip manual screwdriver with a #2 Phillips tip having rounded blade edges, remove all eleven retaining screws from the IF board (the board with all the filters).
- Unplug the multi-conductor header cables from the board, to allow the board to be moved aside.
- Grab the inner edge of the board, and swing the board away from the chassis. Do not stress coax cables on board. Rest board on a stand (e.g. 2 phone books) next to radio.
- Locate FL-96. Using a solder-sucker or wick, and a temperature-controlled pencil iron, desolder 4 filter pins.
- Remove nuts & washers from filter mounting studs. (I think the nuts are M3 or M4.)
- Remove FL-96, wiggling it gently to free pins. You may need to re-heat pins quickly to release filter. The board is G-10, and can take reasonable heat.
- Place FL-44A on board; tighten down studs with nuts & washers.
- Re-solder pins of FL-44A; clean excess flux with nylon brush & isopropyl alcohol. Also ensure that there are no solder blobs or slashes.
- Re-install board and all cables unplugged in Step 4.
- Pull FL-102; insert FL-223, and flip 2 dip switches (per user manual) from AM to SSB.
- Test radio, then replace covers.
Good luck! The whole job should take about 30 minutes.Note that the FL-223 is selected in USB or LSB mode by pressing the [WIDE] button.