Instead of buying a whole new ADS-B antenna to fix the cable problem, I just spent around an hour this weekend in the attic affixing a new connector onto the end of the much-shortened cable (there was quite a bit of slack). My performance improved almost immediately (and the range seems a little better), but we'll give it a week or so to settle out before making more changes (like adding in the splitter).
Soldering tiny connectors while sitting cross-legged on the attic floor was made more bearable by...
- ADEQUATE LIGHTING.
- Bringing up a board that I could clamp a small pair of "helping hands" to and do some cutting on.
- Taking a break halfway through to go retrieve my desk lamp with magnifying glass insert so I could stop trying various combinations of glasses and squinting and actually see what I was working on.