Originally Posted by Tanglefoot
It's a 1/4 wave on 2-meters with a simple inductive trap at the 70cm 1/4 distance from the base. I'm afraid I don't know the properties of an effective trap, but a few spirals seems to do the trick!
The MFJ-1724B. Looks similar to the antenna I use for around town and on trails with low trees, a Larsen NMO2/70SH. It's 1/4λ on 2m, coil a few inches up and center-loaded 3/4λ on 70cm, overall about 19" tall. I would have guessed that was the same. But if it's 1/4λ on 70cm, remember that's about 7" and so the coil is probably spaced about that far up.