Stop twisting wire pairs before you crimp them - it messes up signal integrity

I was troubleshooting a 767's weather radar antenna feed last Tuesday and found the real issue was a guy from the night shift who twisted the RG400 braid into a tight pigtail before soldering the connector. It changed the impedance just enough that the radar showed false returns and flagged a 3 degree error. I've seen this on at least 4 installs this year where people think they're being neat but they're actually creating a mismatch. Has anyone else run into this or am I the only one who bothers checking with a TDR after a connector gets replaced?

2 comments

2 Comments

parkerkim1mo ago

Real talk, nobody checks with a TDR after a connector swap and that's the whole problem. People see a neat pigtail and think it's good work but they don't understand RF physics at all. That 3 degree error you found is exactly the kind of thing that gets blamed on "bad parts" instead of bad technique. I've had to redo three antenna feeds this year because of the same twisted braid nonsense. Stop being cute with the cable and just lay it flat like the manual says.

claire_fisher411mo ago

@parkerkim said "just lay it flat like the manual says" and that's the real kicker. I think manuals are great for the basics, but a lot of those guides don't talk about what happens with phase shifts in longer runs. I've seen a neat install pass a visual check but fail the TDR test because the bend radius was too tight, not even from a twist.