Hi Tor, thanks for the help
...it seems to be proven method as I did quick check and
F/B shifted very close to the original and impedance curve was quite ok.
This was very quick as I already had both sw's.
Actual impedance measurements must wait the monster is up probably next summer...

I think you will find they are very easy to build. The only adjustment
that might be needed is the tip lengths on the driven length, which might
vary somewhat depending on the lead lengths on your balun. But I found on
mine (I built two 6 el/21 Mhz and one 6 el/28 Mhz) that I didn't need to
adjust anything in the actual antenna. No adjusting matching networks
since they are 50 ohm Z anyway.

I used insulated element brackets, if you use metal plates you might want
account for that.

The one thing I don't particularly like about the designs I used is that
they are hard to side-mount (with a rotator) on a tower, since one element
is very close to the center of the boom. But they seem to perform quite well.

Tor
N4OGW