It depends ENTIRELY on how they are foreshortening the antenna. If they are
using super-wide conductors (the entire width of the blade) to get the
foreshortening, then it is a very efficient antenna. If they are using
loading
coils inside with a relatively narrow antenna diameter, it is a very
inefficient
antenna.

The only way to know for sure is to ask the manufacturer for a data/spec
sheet
or cut the antenna open.

Jim


Will one of those SWR meters tell you anything?