Here is a serious synopsis of the DL6WU yagi designs:

----------------------------------------------------------------------------------


Extract from vk-vhf mail list 7th August, 2006:


Author: Graham Selwood, VK4SG:



Here is some of what I've learnt about the DL6WU design...From my
personal
perspective. Instead of using my words, I've decided to use the words
of
several contributors to the VK VHF reflector. If you wish to see who
said
what, the text in the attachment "Identify the guilty" is colour coded
to
identify the author.



This text relates to the history, design tools and overall concept of
the
DL6WU antenna and its variants......remember it's your words, not mine,
and
I have done my best to keep it all in context.



The DL6WU ANTENNA and design tools



Gunther Hoch, DL6WU spent decades on research and development of the
universal antenna now commonly bearing his name. He used cut and try
experimental techniques, sometimes with the aid of a large reflection
free
test range owned by the German Post Office. The outcome of this labour
was a
set of graphical curves. These can be used to design a near optimum
yagi
antenna for any frequency using materials which happen to be on hand,
and
which matches to 50 ohm coax without the need for adjustment. The DL6WU
antenna provided a significant boost to VHF/UHF operators using DIY
antenna
systems.



DL6WU has contributed to a number of amateur publications, but the
first of
his works to reach here appeared in VHF Communications (1977). In it he
presented the basis of his recipe for yagi design, at a time before
computer
simulation was available.



One of the reasons why the DL6WU is so easy to duplicate, is the fact
that
it covers quite a wide bandwidth, so any errors in boom correction make
little difference to the gain. It is clear that a feature of the DL6WU
designs is their insensitivity to dimensional variation.



DL6WUs are not the be all and end all of Yagi's and the man never said
that
they were. They are very good though. It is certainly possible, without
the
slightest shadow of doubt, to get a little more gain for the boom
length and
lower side lobes than DL6WU --- however not without a considerable
amount of
trouble --- so for most people --- it is probably not worth it.



One of the deficiencies of the design, is the first side lobe
performance is
only mediocre. Another slight deficiency of the DL6WU is that if you
stray
from the lengths of 10, 14, 19, 24 etc elements, the front to back
performance deteriorates.



The great thing about the DL6WU is that the design is quite wide band
and
pretty docile to get going, but if you try to squeeze maximum
performance
out the antenna (Gain, F/B ratio, side-lobes etc) then one cost will be
reduced bandwidth over which the antenna has close to modelled design
performance.



So -- absolutely and without question -- the DL6WU designs are not a
problem...  The problem lies in the attempts by various people to
translate
DL6WUs graphs - aka - look up tables into computerized form. During the
last
30 years dozens of experts

have had a go at getting their names in lights by declaring that their
version is an improvement over the original & the reality is that
unless
these optimisations have been carried out by DJ9BV or K1FO & possibly
at the
most one or two others [perhaps G3SEK?] I would not be taking the risk.
In
short some people have taken liberties with the translation from the
printed
graph to the computerized look up table form and falsely labelled their
results as a "program" resulting in the naive acceptance of these so
called
programs.



Most of them used formulas or lookup tables based on one of the sample
Yagi
designs published by DL6WU. No guarantees that they would produce
numbers
correct for any frequency or boom length. One of them was derived from
a
sample design for 1296 MHz, so if you wanted a 144 MHz yagi the program
generated the 1296 design then scaled all of the dimensions by a factor
of
9. Not quite the right way to do it.



If you can understand computer programs you can see whether the
programmer
took the easy way out or did the job properly and derived his numbers
from
the original DL6WU graphs. But if a program is in the form of an EXE
file,
you can't check the code and there is no way of knowing whether it is a
pig
in a poke unless you do some trial runs and compare them with DL6WU's
graphs.



If you design and build antennas based on a faulty design tool, then
you
haven't really built a DL6WU antenna, and all the evaluations based on
a
flawed design are of little value. So to see comments about some
program
being the best and coming up with answers that are very close seems a
bit
inconsistent to me. How close is "very close" and is the difference due
to
representational errors or algorithmic errors? What is the definitive
implementation? Are antennas built to a flawed calculator really DL6WU
designs?



It only takes one test case that produces significantly different
results to
show that computationally, they are different, and the G3SEK, VK3AUU,
and
VK5DJ all produce different spacing and/or length dimensions on the
test
case. I will leave others to argue that 20 to 30mm is insignificant in
application, and that the difference in apparent computation methods is
always insignificant.



There seems to be a level of trust in these tools that is unwarranted.





K1FO has construction software much like DL6WU however an oddball feed
impedance is used which requires a special matching arrangement.  DL6WU
could have done this also for slightly more gain but he wanted to keep
it
simple.

Regarding the K1FO design, I believe it was originally derived from the
DL6WU design.  While it seems to work well, it has lower feed impedance
(22
ohms?) which has several downsides.  Firstly, ohmic losses become more
significant.  Secondly, it requires a more complicated driven element.
If
you follow the ARRL design to the letter, you'll end up with sliding
bars
and a number of contact junctions that could cause problems later in
life
when the corrosion has set in.



In the case of DJ9BV a 50 ohm feed impedance is retained however there
is no
software available to roll your own with materials on hand but if this
is
incorrect I would like to know where it can be found.



Both of the previous alternatives have changed the design more to suit
a low
temperature environment & for a given boom length adds a few tenths of
a db
in gain.  Any antenna system where lobes are in contact with warm
ground, ie
cannot be elevated, is not in a low temperature environment.



One of the deficiencies of the DL6WU design, is the first side lobe
performance is only mediocre. A better result can be obtained by
putting
more taper on the element lengths and also pushing the elements closer
together. This can produce better than -20 db first side-lobe for a 40
plus
element yagi. For most people this would still be a practical length
for 70
cm. Pushed to the limit, this produces a very wide band antenna - 12.5
percent gain bandwidth at -3 db points



Another slight deficiency of the DL6WU is that if you stray from the
lengths
of 10, 14, 19, 24 etc elements, the front to back performance
deteriorates.
However, this can be improved to a null by shifting the LAST director
position. Incidentally, this technique works for most yagi's, much
easier
and more effective than playing around with reflector lengths and
spacing. I
drew attention to this several times umpteen years ago and times since:
A,
if not the major cause of back radiation in a Yagi is due to the
reflected
wave from the front director, that is the one way out there, returning
via
the string of directors to the dipole and arriving in phase with that
radiation which is proceeding backwards from the dipole itself.



Therefore all yagi's, note all yagi's, have back lobes which are
dependent
upon their length from the dipole to the foremost director.
Furthermore if
it can be arranged that this back radiation is in anti phase to that
from
the dipole you may dispense with the reflector altogether and still get
a
reasonable F/B.   Note however that this phasing depends on the
velocity of
the wave along the line of directors -- which in turn depends on the
total
length.

This fundamental fact - along with many other fundamental facts -- was
pointed out at least 60 years ago



So, taking all this info, and other discussion into consideration, what
seems to be the consensus?



Would I be correct in saying that?



1                    The original set of graphical curves as published
by
DL6WU will produce a high gain antenna which is tolerant to
manufacturing in
an amateur environment



2                    The Algorithms produced by Ian G3SEK and David
VK3AUU
Both accurately produce figures that match well with the original
graphical
curves



3                    There has been corruption over time by persons
unknown
to some of the software available using these Algorithms



4                    The software produced by John DrewVK5DJ is deemed
to be
the best source of uncorrupted software available for those not wishing
to
design from the original graphical curves
http://www.corprit.net/~jdrew/YagiCalc.zip




5                    The antennas designed by Steve K1FO, Rainer DJ9BV
and
David VK3AUU Have all developed further the original ideas of Gunther
DJ6WU,
to produce antennas which may have advantages in areas such as gain,
controlled feed impedance, front to back and/or side-lobe suppression,
all
be it at the cost of reduced manufacturing tolerances and/or bandwidth.



6                    If deviating from the lengths of 10, 14, 19, 24
etc
elements in a DL6WU antenna design, some adjustment to the forward most
director position may be necessary to restore the front/back ratio.





To finish with a couple of quotes from the reflector:





To quote a clich? why try to reinvent the wheel [unless you are very
clever]
when in the vast majority of cases it is not necessary to do so?  Why
not
keep it simple, effective & risk free?



The main problem with amateur antennas in this part of the world is not
the
design origin or boom shape but the number of them in the sky!



Also for those new to the field, note that within fairly wide limits,
gain
is strictly a function of boom length, generally within a fraction of a
db,
so don't get sucked in by phoney claims of ridiculous gain from some
manufacturers



Read the last page of:
http://g7rau.demon.co.uk/sm5bsz/antennas/cpudes01.htm




It is clear that a feature of the DL6WU designs is their insensitivity
to
dimensional variation. Some of this goes to the issue of how much of
that
tolerance one consumes before drilling holes and cutting, alternatively
stated as "measure twice, cut once".



Having done the "measure twice" thing, I am on to drilling and cutting.



BUILD IT



Compiled/written by Graham Selwood VK4SG



Quotes from:



Ian Cowan VK1BG

Owen Duffy VK1OD

Gordon McDonald VK3ACC

Charlie Kahwagi VK3NX

Dave Smith VK3HZ

Trevor Benton VK4AFL.

David Tanner VK3AUU

John Clark VK2TK

John Martin VK3KWA

Graham Selwood VK4SG


----------------------------------------------------------------