The Yaesu FT-857 has slots for two accessory filters. Many FT857 users add a narrow CW filter (500Hz and 300Hz filters are available), some add a 2.3Khz SSB filter, some add both a CW filter and an SSB filter.
In May 2018 I added a 500Hz CW filter to my FT857 and have been very pleased with the performance under crowded band conditions and when working weak signal CW.
I purchased my filter from Ham Radio Outlet. I’m certain other amateur radio dealers carry the filters, however, I’m a long-time HRO customer and am pleased with their service.
Here’s a photo of the filter. It is installed in this orientation — that is, install it with the label facing up. Note the two jacks: on the left is a 3-pin connector, on the right is a 4-pin connector.
Here are instructions for installing the filter.
First: Disconnect everything from the FT-857 — power, antenna, headphones, key — anything that’s connected to it. Then, remove the seven tiny screws that secure the top of the transceiver.
Look closely at the speaker — note the two screws on either side of the speaker — do not remove these as they hold the speaker in place. Instead, remove the other three screws on the top — one at the rear (between the homemade CAT and DATA labels) and two toward the front — remove the screw that is between the forward speaker screw and the front panel, the other is in line with the one just described and to the rear of the on/off button. On each side of the rig are two screws (total four). When you look at the side, you’ll see threaded holes used for the rig’s mobile mount and two small Philips head screws — remove the Philips head screws — four, two on each side. You’ll need a thin-bladed screwdriver or a knife blade to slide under the panel and pop it off.
BE CAREFUL WHEN YOU REMOVE THE TOP PANEL because the speaker comes out with it, however, the speaker is connected to the main PC board . . . if you snatch the top off, you can rip out the speaker wiring — gently remove the top, watching for the speaker wiring.
Set the top aside. You can leave the speaker connected, or, unplug the speaker leads from the main board.
Once inside the radio, look at the left rear where you will see two filter positions — bottom left corner in this photo.
Here’s a close-up of the two filter positions.
You can install your filter in either position, FIL-1 or FIL-2. Look at the connector pins sticking up from the main PC board at either end of the filter locations — note that each filter position has a 3-pin connector at one end, a 4-pin connector at the other end.
Here’s a photo of the filter installed. Carefully position the filter, label up, over the 3-pin and 4-pin connectors sticking up out of the PC board. Being careful not to bend any of the pins, press the filter into place.
The radio should recognize the filter. If you unplugged the speaker, re-connect it. Put the top back on with all seven screws. Re-connect power, antenna, etc. Turn the radio on. Press the FUNCTION button momentarily and use the SELECT knob to go to Menu position n. If you put the filter in FIL-1, press the B button to select the filter bandwidth — 300, 500, or 2.3. If you put the filter in FIL-2, use the C button to select the bandwidth. On my rig, when I turned it on and went to Menu-n, the filter bandwidth was already selected.
To use the filter, go to Menu-n and press the B or C button — the one that shows the filter bandwidth. An arrowhead will appear pointing to the filter bandwidth and you will hear the effect of the filter switching in. To switch the filter out of the circuit, press the B or C button and the arrowhead will disappear.
Here is a YouTube video of an FT857 with a 500Hz CW filter installed. The operator plays with the radio — to see the CW filter operation, go to about 3:40 in the video and watch from there to about 4:04.