You need to be aware that there's a good chance that this might not
work, or at least not like you think it will.

An impedance transforming balun includes one or more windings connected
across the two conductors. The impedance of the winding itself appears
across the conductors as a shunt impedance. In order for the winding
itself not to have an appreciable effect on the system, the winding
impedance must be at least several times the impedance of the circuit to
which it's connected. A rule of thumb is that it should be a minimum of
5 times the impedance of the circuit, with 10 times being better. That
means that a 4:1 balun intended to transform 200 to 50 ohms would have a
high-Z winding impedance of around 1000 - 2000 ohms. When a balun is
designed for multiband use, the impedance is likely to be on the low
side at the lower end of the frequency range, since this is where it's
hardest to get high impedance. Also, if the impedance is too high at the
low end, you can run into resonance or other problems at the high end.

The bottom line of all this is that you're likely to be putting a
winding impedance of somewhere around 1000 - 2000 ohms in parallel with
your 800 ohm antenna. If this impedance is pretty purely inductive, it
will have a profound effect on the tuning of the antenna. If it's fairly
resistive, it'll also dissipate a good fraction of the power you apply
to it. So don't be too surprised if you see either or both these effects.

If you have an antenna analyzer you can terminate the high Z end with
around 800 ohms of resistance and measure the input impedance. I'm sure
you won't see anything that much resembles 50 + j0, at least not over
much of a frequency range. If your antenna isn't resonant so it doesn't
present close to 800 + j0 ohms to the balun, you'll likely see
additional effects.

Roy Lewallen, W7EL