I'm experiencing IMD issues with my current audio interface setup when running FT8 and FT4 modes. Running excessive IMD causes decoding errors especially in crowded band segments, though both modes can tolerate modest distortion thanks to forward error correction. My current setup is a homebrew interface with an FTDX-101D, and I'm seeing some splatter that's making me unpopular with adjacent ops.

Looking for recommendations on commercial interfaces that provide better linearity. I've read I should set RF output to no more than 50% of rated max and aim for no more than 80% of configured power during transmission. Anyone have good results with specific interface models for multi-carrier digital modes?

The SignaLink USB is hard to beat for clean audio interfaces. Keeping well within the linear zone and clear of harder ALC onset minimizes splatter and maximizes decode reliability. I run mine at about 40% drive level with my IC-7300 and get excellent results on both FT8 and FT4.

Check your computer's audio levels too - many folks overdrive at the PC side. Set Digital Input Level or DIG Gain to around 50% in the rig's menu to place the input stage in its optimal range. Also monitor your signal with an external receiver if possible.

JS8Call is more sensitive to linearity than FT8/FT4 due to its extended message structure, while PSK31 demands high linearity for reliable decoding. If you plan to use multiple modes, invest in a quality interface from the start. The Digirig or MFJ-1204 are both solid choices.