K7ITM wrote:

If you need the mechanical
antenna to be shorter than 48 inches, just wind that length of wire in
a spiral, spaced out as much as you can accommodate. Try that and see
how it works. Easy enough? If you need higher performance, that's
possible, but in general very short antennas won't be as efficient as
straight antennas long enough to be self-resonant at the operating
frequency...

Is that all a rubber ducky antenna is? 48" of wire wound around a
flexible core of some type?

If so, what do I look for (type, model, etc.) if I want to purchase
one to try out?