click to enlarge.
Instead of folded, I am using open dipoles in my DJ9BV.
Overall length 980mm 1 cm gap in the centre.
3 Watts forw. gives approx. 15 mW reflected power.
Balun is 1/4 wave aircel 7 coiled around the nonconducting boom.
In case of a conducting boom the balun has to be placed at some distance of the boom.
Following SM5BSZ's procedure, the performance of the balun can be checked as follows:
Place a inductive loop with a rectifier at the end of the antenna.
Connect the rectifier with twinlead on a voltmeter (use some chokes near the rectifier to avoid the wire is picking up rf, instead of the loop.)
Point the antenna into the sky, driven element >= 1 mtr. above the ground.
Now feed the antenna with a few Watts.
When you move your hands along the transmission line there should be no fluctuation in reading on the voltmeter.