C. J. Clegg wrote:
. . .
If you guys say coax traps are a sub-optimal approach I'll take your word
for it.

But, the things you all are saying about traps coming with a lot of
baggage that no one ever thought of is making me nervous. :-)

It's not exactly a new concept, trap antennas have been used with great
success for what, 80+ years now?

The coax trap is a relatively new idea. I don't think it was around
until the '70s. They definitely have their place, being cheap, simple,
and rugged. And the loss is minimal in a lot of cases. Note, however,
that there are two ways of connecting the coax. In one, the center of
one end of the coax is left open. In the other, the shield of one end is
connected to the center conductor of the other, and the two remaining
ends are the external connections to the trap. The latter method gives
an L/C ratio that's generally more favorable.

As for the "great success", almost no amateur is able to tell when he's
getting a couple of dB loss, which is about what you typically get with
an unfortunate trap/band combination. I've mentioned that this is what
happens and how I've avoided it, but most people happily accept it, if
it happens, without worry. Each to his own.

If I forget the coax trap idea and go with a resonant coil-and-capacitor
approach on, say, a 1.5" coil form (which Hamcalc seems reasonably happy
with after warning me that 2" was too big and 1" was too small), what
should I look out for?

For your application, I'd probably use coax traps. Using a separate coil
and capacitor aren't a guarantee against loss. Even a pretty good trap
can introduce a fair amount of loss if it ends up looking like a big
inductor in the wrong place in an antenna on a band below the trap's
resonant band. Or if you put it in a point where there's an extreme high
voltage between the ends on the band where it's resonant. Without the
ability to measure trap characteristics and do some modeling, what you
end up with will be determined entirely by luck. But as I said, you
probably won't notice the difference anyway.

Roy Lewallen, W7EL