I've carried quite a variety of interesting stuff on domestic flights
many times before and after 9/11, including homebrew gear, mag mount
antennas, cables, batteries, etc., and on a few international flights.
My checked bags always end up with a card saying they've been inspected,
but that's all. The carry-on is sometimes flagged for hand inspection by
the X-ray operator, and I've learned to leave the interesting stuff on
top so it's easy to find during the hand inspection. Sometimes the
problem is simply that they can't see what might be hidden under a metal
box (which I assume is why they require computers to be removed from
their bags). If you're in a hurry, you can dump all the interesting
stuff into one of the plastic bins so it's in plain sight and they won't
have to search through your bag for it, and so it won't hide any of the
bag contents from the X-ray -- I've done that on a few occasions. The
hand inspection usually only takes a couple of extra minutes. There's
nothing illegal about carrrying radio or electronic gear -- they just
need to know that it won't explode, give off noxious fumes, or be used
to stab somebody. If it won't, they could care less what it is or does.
It's not a big deal at all.

MP3 players, USB, Ethernet, and telephone cables, GPS receivers, HTs,
cell phone chargers, power supplies and voltage converters, and other
common modern trappings generally sail right through the X-ray machine
without a comment.

Roy Lewallen, W7eL