Peter wrote:
Ok so there are lots of different designs that supposedly have
different strong points. Suppose I just want to go for maximum dB. How
do I achieve that? Does anyone have a site that explains what
parameters to use to achieve that?

I hope not. If a long yagi is optimized for gain and nothing else, it is
usually quite poor in other respects: large sidelobes; narrowed,
sharp-pointed main lobe (hard to aim accurately); poor front/back ratio;
inconvenient feed impedance; poor gain and SWR bandwidths; and poor
tolerance to constructional dimensions, detuning by raindrops, frost
etc.

The same has been found many times over, whether you do it by
traditional cut-and-try or by computer - the computer only gets you to
the same dead-end faster.

Modern optimized yagis achieve almost the same gain, but don't have
those vices to anything like the same degree. They are much easier to
build, match and aim, so in practice you'll almost certainly achieve
*more* gain.


And can anyone explain this. When I ran the DL6WU Antenna Design
Program

There are dozens out there, but it's very clear you mean the one on my
site.

and fed in my parameters (433.92MHz, 5mm thick elements,
plastic boom) it gave me a set of lengths and spacings and a supposed
dB of 12.1. But it had the DE and D1 3.4mm apart from centre to centre
meaning that with 5mm rod they were actually touching!

You're so right - sorry, there was a bug.

That program had been reliably getting all the important things right
for about 20 years, but recently I blindly accepted someone else's
"correction" for a small error... which triggered an even larger error.

As of this message, the revised program is back on the site:
http://www.ifwtech.co.uk/g3sek/diy-yagi/

The bug only ever affected the shortest yagi that the program would
design... which was the one Peter wanted. Thanks for spotting it, Peter.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek