Hi Martin,
I saw the article, the balun is a useful item to have in the shack, and the design seems OK. However they have got the 4:1 and 1:1 unbalanced ports swapped around in the drawing.
Leave the unused ports un-terminated. Don’t leave even short lengths of coax connected to the unused ports as this will add varying impedance loads which will adversely affect performance.
10 turn 1:1 coax baluns does not provide sufficient choking impedance on 80 or 160m, although they are generally adequate on 40m and above. If you intend to use your doublet on 160 or 80m use several turns of coax through something like a 240-61 ferrite core (or similar).
My home brew coax 4:1 balun is not good when driving into low impedance capacitive loads (event though it has a very low through loss when terminated correctly), so I’d suggest the T200-2 transmission line balun as per the Radcom article would be better. Please make sure you wind the transformer neatly with suitable diameter wire, as this has a large effect on performance, particuarly at HF frequencies. There are some really bad examples shown in construction articles on the internet. Winding a transformer badly can easily result in 3 or more dB loss, so I'd recommend making loss measurments, when you have built yours. You can find some easy methods on my website.
Also for 160m you can strap the doublet as a T and feed it against ground. If your tuner can’t handle the low impedance load reverse the 4:1 balun and use the unbalanced ports as a 1:4 UnUn.
Regards,
Martin – G8JNJ
www.g8jnj.webs.com 
