Ian White GM3SEK wrote in
:

....

No problem. It's a standard technique for matching yagis, for example:

http://www.mydarc.de/dk7zb/start1.htm
(click the third item in menu list)

Ian,

The DK7ZB match (http://www.mydarc.de/dk7zb/images/match-12+28.gif) is
interesting. Ideally, the transformation sections (the inside of the coax
TL) are an electrical quarter wave, and the balun (the TL formed by the
outside of the coaxes in parallel and the boom etc) is a quarter wave.

I would be surprised if constructions typically shown achieve that
optimisation, due at least to the use of solid PE dielectric inside the
line, and a air / vinyl dilectric outside.

The construction at
http://www.mydarc.de/dk7zb/DK7ZB-Mat..._Isolation.jpg is quite
complex, containing what might be seen as as an electrical quarter wave
transformer and the balun formed of a U shaped stub of physical length
0.5*0.25*0.66=0.08 wavelengths shunting one side of the DE, but this stub
lies with its hot side against the cold boom forming another o/c TL
element. If the balun shunts the DE with a high impedance, it will be due
to not just the loop length, nor just the s/c stub length, but parallel
resonance with the boom / half loop o/c stub.

If that is the case, the construction is not simply explained by the
first diagram that I referenced above.

I am not suggesting that this implementation doesn't work, but that there
are design parameters beyond those implied by the electrical circuit
given.

Thoughts?

Owen