Fred,
I have a double Bazooka for 20, 40 and 80 meters and they work fine!
There is a formula for them on the coaxial dipole site. Mine are home made.
We just cut the Coax a little long for the antenna and that way you can tune
them by folding the ends back until you get the S W R where you want it. The
feed line is cut from the same run of coax which helps keep the valocity
factor the same for the whole antenna. I have had mine up for going on 5
years and they are still less than 1 to 2 S W Rs. The 80 is good from 4000
to 3600 with out a tuner.
KF5UB Richard