And, consider: even then, It might not work as it does on another
frequency. Have a friend (this years ago), who modeled the Komosko-
Johnson yagi for 2 meters (a 13 el, antenna , that was emperically
designed), long before modeling programs, and then antenna range
measured. This was a staple of the old VHF handbooks, and the
ARRL handbooks for years, and seemed to deliver exceptional results.
He had pull at his local company (not to name them)! and had an
EXACT copy made for 1296, and then entered it into a antenna contest-
it failed misserably! (this not only was element length/Dia, spaceing,
,but BOOM diameter/length)!! It was (and is) a work of ART,
but it wont make his retirement check (or Contest Score)
any higher! For those that
wish to try it- look for those names, or for W2NLY-W6QKI in the
ARRL handbooks mentioned. But it must leave to the builder one
of the following conclusions: 1) It was great on 144, but a dog
on 1296, or: 2) It wasn't the greatest design , for even 144 (tho
it compairs favorable with the range patterns that were shown
in the VHF handbook, for 144)! As info, Jim NN7K

David wrote:
Ian,

Thanks for that.

I did previously look at your site and bookmarked it. I am going to make
up the element cutting jig and bending jig (for when I want to
experiment with folded dipoles).

Great site.

Regards

David

Ian White GM3SEK wrote:

David wrote:

Hi,

I have a design for a Yagi antenna at 436MHz and would like to scale
it to 921 MHz. The calculations I used from the understanding I have
obtained from reading various articles appears below.

Would someone be kind enough to advise me if this procedure and
values look correct ?


[...]


Regards

David Huisman




The basic principle of scaling antennas according to wavelength is
that you must make an *exact* scale model. That means scaling every
dimension, and not adding any new or different 'features'.

Often that isn't practical for mechanical engineering reasons, so then
you need to apply corrections. However, you should still aim to keep
those corrections as small as possible. For example, simple scaling is
likely to produce odd, unavailable values for the element diameter, so
it's OK to use corrections to change to the nearest commercially
available diameter. But if you also decide to double the diameter, the
correction is more risky - you're entering the territory of a
completely new design.

Sorry that I don't have time to check your particular dimensions in
detail, David, but you can find resources for scaling and
constructional techniques on my 'VHF/UHF Long Yagi Workshop' pages.
There is a downloadable program which leads you through the relevant
questions, and also a link to an online Javascript version.

(From about 1200utc I will not have access to this newsgroup for the
next few days, so I hope the above will keep you going.)