Category : Science and Education
Archive   : YAGICA.ZIP
Filename : YAGICAD.HLP

YAGI COMPUTER AIDED DESIGN By Paul McMahon VK3DIP
Version 4.1 June 1991
Copyright Paul McMahon 1991.
A Disclaimer and Shareware Notice appear at the end of this file.

This file is in plain text in YAGICAD.HLP and may be printed if
required.

BASIC GETTING AROUND.

YAGICAD uses a combination of 'Lotus' like and 'Pop up' like menus.
These menus can be traversed by using the standard cursor
positioning keys, ie up, down, left, right.Once highlighted the entry
can be selected by the enter or carriage return key. In addition for
the 'Lotus' like ones the first letter of the entry will also select
the entry (no enter required).

SPECIAL KEYS.

Apart from those keys already mentioned several other keys have
special functions:

ESC
This key in menus, or the file chooser, will 'escape' from the
current level to the next one up. Alternately in data entry or editing
modes it will terminate the edit and return the value to the default.
In most cases ESC will not terminate an edit.

HOME
This key is used in the file chooser and the main edit routine.
In the chooser it returns you to the top of the file list.
In the Editor it gives you some quick help.

END
Similar to the home key in the file chooser this takes you to the
end of the file list. In most editing routines it is the only key
that will end and exit the edit.

PAGEUP and PAGEDOWN
These keys have the normal effect in the edit and help view modes.

INS and DEL
These keys are used in the main edit routine to insert or delete
Yagi elements.

USING THE FILE CHOOSER

The file chooser is a pop up box which will initially show the
current directory contents both files and directories. If a file
is selected then it will be opened if it is a YAGICAD data file.
If a directory is selected then that directory will become the
current one and the new contents will be shown. The '..' entry
is a special directory and if selected will take the current
directory up to the previous level. The chooser cannot change the
current disk drive. If this is required then select the DOS SHELL
menu item and enter the appropriate DOS command and type EXIT to
return.

WHAT CAN YAGICAD DO?

YAGI is a fully integrated analysis and design package for yagi
aerials. With it it is possible to enter a base design from scratch
or use one of a number of preprovided saved well known designs. This
design can then be optimised or scaled to suit particular
requirements. Once this has been done a matching unit can be
estimated and overall performance characteristics can be calculated
and displayed graphically. Also available are radiation patterns and
hardcopy print-out of results. Allowances in an analysis can also be
made for element cross sections other than simple circular ones, as
well as boom mounting techniques.

DEFAULTS AND SUGGESTIONS.

When ever YAGICAD prompts you for some value it will suggest a value
that based on past experience may be suitable. These values can be
over written if required.


AN EXAMPLE.
The operation of YAGICAD can be most easily understood by studying an
example.

Suppose you are interested in a yagi for two metres.

1. Get the base design by either typing it in using the Edit option
with Insert, or use one of the saved designs and choose something
that looks close to your requirements.

2. Say you choose to use the saved NBS 6 element design. So you load
this.

3. Scale the base roughly to the new frequency say 147 MHZ using the
SCALE function. You could also have changed the element diameters
to some new value if desired also using the SCALE function, or
even allowed for non circular cross section elements by using an
EFFECTIVE DIAMETER CALCULATION options are "L" shaped,
rectangular, or folded dipole.
You could have also edited the saved data using the EDIT functions
to add or delete an element etc..

4. Do some BASIC CALCULATIONS to determine the gain, front to back,
etc., for this new design. A polar plot of front to back could
also be done at this time.

5. The design could now be optimised for MAXIMUM FORWARD GAIN, (FRONT
TO BACK, RESONANCE of the DRIVEN ELEMENT, or MINIMISE LARGEST
SIDELOBE could also have be chosen). This is done by selecting
the appropriate entry from the CALCULATION menu and selecting the
value to be varied,ie. a spacing, length, diameter, or
frequency.

6. Steps 4 and 5 are repeated as many times as is necessary. When
satisfied you could do a SWEPT FREQUENCY RESPONSE to see how the
design performs over a range of frequencies.

7. Assuming all is OK you could now proceed to calculate a matching
network for your design. You select MATCH from the TOOLBOX and say
decide to use a FOLDED DIPOLE. (GAMMA, or TEE matches could also
have been used). Let us say you are going to use a 4 to 1 coaxial
balun with 50 ohm coax ie the required input impedance to be
matched is 200 ohms. The program gives you the required diameter
of the folded part of the element. If you had chosen to use a
gamma match then it may have been appropriate to RESONATE the
driven element to some negative (Capacitive) reactance. A figure
of say -15 to -20 Ohms has been found to give better results than
a true resonance ie. 0 Ohms.

8. You could now get an OVERALL RESPONSE of the design including the
effect of the matching network, but it would be best to allow for
the folded dipole by first CALCULATING its EFFECTIVE DIAMETER and
EDITING in the new effective diameter of the driven element. Steps
6,7, and 8 could then be repeated to ensure that nothing untoward
has happened. The final resultant plot as with all other graphics
can be printed out on your IBM or Epson printer.

9. You may now wish to allow for a metallic boom. This is done using
the BOOM item in the TOOLBOX. The values suggested by YAGICAD
allow for the element being mounted though the centre of a
circular cross section metal boom with good electrical contact.
You can allow for non circular booms with the EFFECTIVE DIAM's
tool. If the elements are to be mounted not through the centre of
the boom the correction factor can be accordingly reduced.

10. The final results could now be printed out using the PRINT
function.

11.Finally the new design can be saved to disk for possible future
use using the SAVE FILE option. In fact if you come up with some
particularly good design why not send the data file to a friend
using packet, or put it on a bulletin board.

12.You could now build the yagi feeling reasonably sure that it will
behave at least close to the calculations.


HOW YAGICAD WORKS.

YAGICAD uses a simple form of what is known as the 'Method of
Moments'.This method is similar to that used in programs like
MININEC, however YAGICAD uses a small number of piecewise sinusoids
to represent the currents flowing in the elements rather than the
pulse functions found in MININEC. This does not make YAGICAD any
better or worse than MININEC based programs, however it is different,
and because it is different, and uses different assumptions the
results obtained will also be slightly different. In fact there are
a large number of different ways to model antennas, and an even
larger number of possible assumptions and simplifications that can
be made. Another variant was that used by Lawson in his works for
Ham Radio Magazine. This is known as the induced EMF version. All of
these versions give slightly different results, and all are good in
some situations and bad in others. Generally there is a basic
agreement however on how a particular antenna will behave. In other
words don't expect the numerical answers given by YAGICAD to be
exactly the same as given by some other program, however general
trends should be common. In fact YAGICAD has been specifically made
to be conservative with its answers and for example will usually be
somewhere up to about one dB lower than the gain claimed by the
originators of some designs. Note YAGICAD gives gain in dBd ie. gain
relative to a dipole, may antennas specs give gain in dBi ie gain
relative to isotropic. If you wish to convert between the two then

dBd = dBi + 2.15



WHAT YAGICAD WILL NOT DO.

THIS PROGRAM IS BASED ON A THEORETICAL MODEL OF A YAGI ANTENNA, MANY
ASSUMPTIONS AND SIMPLIFICATIONS HAVE BEEN MADE. THE RESULTS OBTAINED
WITH THIS PROGRAM MUST THEREFORE BE TAKEN WITH SOME CAUTION. IN OTHER
WORDS IF YOU BUILD AN ANTENNA THAT HAS BEEN DESIGNED WITH YAGICAD
DON'T EXPECT TO GET IT WORKING EXACTLY AS CALCULATED WITHOUT AT LEAST
SOME EXPERIMENTAL ITERATIONS. IE. YAGICAD IS NO SUBSTITUTE FOR A VSWR
METER ETC., AND AT LEAST SOME TRIAL AND ERROR. ANYONE WHO DOESN'T AT
LEAST USE A VARIABLE CAPACITOR OR HAVE SOME MEANS OF VARYING A GAMMA
ARM LENGTH IS EXPECTING TOO MUCH FROM THIS OR ANY OTHER ANTENNA
PROGRAM.


In order to get this program to run in reasonable times on a PC a
number of simplifications have been made. In practice these should

not make very much difference at all to far field results such as
patterns and gain, however they can have an effect on near field
results such as input impedance. Care should thus be taken when
working in this area. YAGICAD 4.1 can make allowances for a metal
boom, however it will assume that the element is mounted right
through the centre, you can however override the auto factor with a
more accurate one of your own. All calculations are assumed to take place in free space.

Some common sense should also be exercised when optimising designs
once you are in the area where YAGICAD is varying lengths or spacings
by less than a millimetre. Sure extra gain is being obtained but you
will have to fine tune your final antenna with a nailfile, so be
practical and you will get results that are close to calculations.

YAGICAD 4.1 is also limited to yagis with less than 24 elements.

EXPERIMENTAL VALIDATION

Not withstanding the very important caution above, YAGICAD has been
around in various versions for some 4 or so years. In this time I
(VK3DIP) alone have built at least a dozen or more different yagis as
designed by this program. Others have built many more. In all cases
known to me the antennas did work more or less as designed,(after
some tuning).

My original motivation for the program was to be able to design
antennas that would be good for Two Metre Fox Hunting, as opposed to
the maximal gain type usually detailed in books etc. So I have also
had quite a bit of testing of patterns and there is no doubt that the
yagis designed with this program have patterns much like those
calculated.

Similarly Yagis designed with this program have done well when gain
was required. For example the VK3DIP 6 element design given in the
standard designs has won at least two antenna gain measuring
contests, and has been used extensively on field days etc. It is a
classic example of what can be done with this program. The design
criteria were that it would be for Two Metres, (down in the SSB )
part of the band, would have a boom of as close as possible to two
metres in length. ( this was the maximum length boom allowed in one
of the gain contests) and it would have a largish gap at about the
centre of gravity to facilitate mounting. I was able to achieve this
design with a few hours work using YAGICAD rather than many days of
trial and error.


DISCLAIMER

In no event or way will the Author be responsible or liable for any
damages, including any lost profits, lost savings or other incidental
or consequential damages arising out of the use of or inability to
use these programs, even if theAuthor has been advised of the
possibility of such damages, or for any claim by any other party.

SHAREWARE NOTICE

PERMISSION TO COPY:

Clubs and other non-profit organisations are granted permission by
the author to freely copy these programs and documentation and share
it with their members, so long as:

1. No price is charged for the software or documentation.
However, a distribution cost may be charged for the cost of the
diskette, so long as it is not more than $10 total.

2. Club members are informed of the user-supported concept and
encouraged to support it with their donations.
"
3. The program or documentation are not modified in any way and are
distributed together.

THE USER-SUPPORTED CONCEPT.

User-Supported Software
If you are using this program and find it to be of value your
contribution will be appreciated,($20 is suggested) and should be
forwarded to:

(INTERNATIONAL BANK CHEQUE, MONEY ORDER, OR EQUIVALENT ONLY PLEASE)

PAUL McMAHON VK3DIP

47 PARK AVENUE WATTLE GLEN
VICTORIA AUSTRALIA 3096

Regardless of whether you make a contribution,
you are encouraged to copy and share this program, though some sort
of remuneration might go some way towards proving to the wife that
all this late nights playing with computers and radios is worth it.


CREDITS

This program could not have been what it is without the following:

Ham Radio Magazine
A sadly missed source of things technical. Over the years I have
never missed a May issue. In particular the articles by Lawson in
the early 1980's. Joe Reisert, and Bill Orr for the many snippets
here and there.

YAGICAD Users.
The feedback from users is always appreciated.

I can also be contacted via Compuserve 72050,426

73 and good designing PAUL McMAHON VK3DIP.