Here is the basic working model on how to put together an aircore balun for hf (3mhz-30mhz).

Use 40mm diameter white pvc pipe. Drill 3 holes at the top a,b,and c. Put stainless steel nuts
and bolts.

Use insulated multi-stranded seperate wires (similar to lamp cords or speaker wires).
Wind them tightly (10 turns and where they end, mark the three points and drill (x,y,z).
a terminates in x, b in y and c in z.

Next cut 2 wires which will serve as jumpers from a to y, b to z.


----------------
| o o o |
| a b c |
| |
| |
| |
| |
| |
| |
| x y z |
| o o o |
----------------

Secure these on to the stainless steel bolts with nuts.

Antenna will go to a and c. Coax will feed as centre code to x with shield to z.

That is all.

4:1 balun is within the antenna design document under antenna section.