Simtel MSDOS - Coast to Coast/simteldosarchivecoasttocoast2.iso/hamradio/yagimax.zip/READ.ME

Text File | 1990-12-31 | 12KB | 226 lines

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              YAGIMAX 2.21                      1/91

                     By Lew Gordon, K4VX

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The YAGIMAX program represents my latest attempt at antenna modeling
software. It is based upon the assumption that the antenna is
monotapered. The algorithm used for YAGIMAX is not derived from MININEC
as was the case with all versions of YAGINEC, but is based upon the
asumption that correctly designed Yagi antennas have a sinusodial
current distribution which is well behaved. For correct results this
requires that the user input realistic dimensions when using YAGIMAX.

In order to expand beyond the 10 element limit of YAGINEC for VHF and
UHF antennas, YAGIMAX has been written without help screens. Most of
the information contained in the YAGINEC help screens is applicable
to YAGIMAX. All files are transportable between YAGINEC, YAGIMAX, and
TAPER.

If you are a previous user of YAGINEC, the first thing you will
observe is that YAGIMAX is exceedingly fast compared to YAGINEC.
This is a result that the elements are not segmentized and
massaged through Gaussian elimination with partial pivioting matrix
inversion techniques (the real time consumer in YAGINEC/MININEC),
but derived from the sinusodial current assumption mentioned above.

To calculate the performance of an antenna using tapered element
construction, the TAPER program must be used to determine the
monotaper equivalent lengths of each element. A file can be created
by TAPER to transport the dimensions to YAGIMAX.

Where YAGINEC will allow the user to model interlaced elements for
several bands (up to a maximum of ten elements), YAGIMAX will not
provide as accurate results. This is because the current distribution
on an element somewhat longer, or shorter, than one half wavelength
will not have exact sinusoidal current distribution. With this in mind,
the computed performance of a Yagi over +/- 20 percent from its resonant
frequency may be inaccurate using YAGIMAX.

The user will notice that most of the entries become cued after first
usage. Any cued prompt is entered by hitting <RET>. This is done
because I am basically lazy when making repetitive entries. It addition,
the cued numbers will probably provide better graphics. I have assumed
that this program will be used for amateur radio antennas, thus the
cueing is relative to typical ham bands. Any entry can be overstruck,
however.

The maximizing feature is not perfect, but can be used on an element
by element basis to maximize either forward gain, or front to back.
Each element change is cycled through the algorithm three times to
provide a glimpse of what the VSWR is doing at preselected low and
high frequencies. Each change is displayed on the screen for the user
to observe. In many cases the user may want to check the list and
manually re-enter a chosen dimension rather than accept the maximizing
output. There will be some cases where a "runaway" optimization will
occur. This can be halted by pressing the escape key. This can occur
frequently in two or three element designs.

Although it is included as a choice for maximizing, the driven element's
length should never be used for optimization as it really has very little
effect upon a Yagis performance except for feedpoint impedance. Also
2 and 3 element Yagis can display some rather unusual (and unusable)
results when optimizing for forward gain using spacing adjustments. The
feedpoint impedance can proceed to values less than one ohm! YAGIMAX only
calculates directivity, not true gain which must include losses. The
efficiencies of these very low feedpoint designs becomes very low.

The results of YAGIMAX appear to be within 0.3 percent of those
obtained with NEC2 when using ten segments or more for calculation.
The speed of YAGIMAX is about 50 times faster than YAGINEC using
8 segments per element. As with YAGINEC the more elements in the
antenna, the slower the calculations.

YAGIMAX will run in systems without a math co-processor but as with
any math intensive program, much slower. A 20 element Yagi requires
about 90 seconds per frequency step using an 8 mHz machine with no
co-processor. The same antenna on a 20 mHz 80386 Gateway 2000 with
80387 co-processor performs 20 steps in 40 seconds.

YAGIMAX 1.03 was the first general release of this program. As with
all my programming efforts, YAGIMAX is shareware and is placed in the
public domain. It is not to be sold or used for commercial gain.
While I have made every effort to reduce bugs or other problems,
I will not be responsible for any problems encountered from using
YAGIMAX.

Computers equipped with an EGA and VGA monitors can expand the
graphics capability of YAGIMAX by using YNINST.EXE to change the
YN.SCR file to provide higher resolution than  CGA screen.
EGA and VGA also increases the number of elements and frequency
steps to 38 and 45.

VSWR plot will allow the user to move a frequency flag over the
plotted curve by using the UP/DN cursor keys. The frequency
represented by the cursor is displayed in the upper right
hand corner.

The "VIEW" of the Yagi shows the center of gravity (CG) of the
antenna.It assumes that all elements weigh the same and the boom
is uniform along it's length. The CG dimension is measured from
the reflector end.

Linear plotting of the results of Gain, F/B, and VSWR vs. frequency
is provided. Those not familiar with the Smith Chart may find this
display more conventional and  understandable. However, if "off the
wall"  frequency steps are selected, you may get an "off the wall"
display!

E and H plane plotting in both free space and over perfect
ground is provided. The algorithm used does not calculate the effect
of mutual coupling between the stacked antennas, but assumes they
are stacked sufficiently far apart to have minimal aperature overlap
and mutual interreaction. The high angle lobes will be much lower in
magnitude in actual practice over real earth as the reflection
coefficient over real ground at the high angles drops drastically.

Free space plotting of stacked Yagis in both polar and linear forms
uses array factor for the antenna based upon uniform spacing.
This feature allows inspection of the sidelobe levels of stacked
arrays for VHF/UHF applications in moonbounce, or where reduction
in the noise pickup from the sidelobes is critical. When using free
space H-plane stacking to examine the the sidelobe levels, a -13 dB
line may be toggled on and off by pressing <Z>. The -13 dB level
is the accepted point at which maximum stacking gain can be
achieved commensurate with sidelobe reduction.

For Yagis with 20 elements or less the plots are made in 1.0 degree
steps. Yagis with more than 20 elements are plotted in 0.5 degree
steps (only available with EGA/VGA). The doubling of the steps for
longer boom antennas with greater than 20 elements almost doubles
the processing time, but this was felt to be worth the delay due to
the complex sidelobe structure of these antennas.

The LINEAR plotting screen can be redimensioned to plot +/-  30
degrees to provide close-in examination of the immediate sidelobe
level. This feature is useful when plotting many element stacked
arrays in free space. Simply press <S> to toggle the scale from
+/- 180 to +/- 30 degrees scale.

The Design Scale radius scaling algorithm described in Lawson's
Yagi Antenna Design pages 7-3 to 7-5 is used to provide an accurate
method of transferring the design of Yagi from one frequency to
another.

Versions after  2.15 incorporates a empirical algorithm to compensate
for the frequency descrepancy between NEC2 and YAGIMAX. This
descrepancy appears for large diameter/wavelength elements such as
are used in VHF/UHF Yagis. Actual NEC runs of several antennas with
varying element diameters were made and the compared to YAGIMAX.
The self-impedance algorithm in YAGIMAX was then altered to compensate
for the descrepancy.
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All programs on this disk were written and compiled using Microsoft (R)
QuickBASIC 4.5 (C) and do not require the presence of BRUN45.EXE
to operate as they are stand-alone versions. The programs were written
on a Gateway 2000 80386/387 20 mHz computer operating under DOS 4.01.

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General tips:

To generate data for a 2 element Yagi where a director is used, simply
enter the director length as a reflector and then place the driven
element behind the director by entering the spacing as a negative number
as in the example below:

  Reflector             31.000                0             0.8750
  Driven element        33.000          -9.5000             0.8750

The numbers will come out correctly.

Try hitting <RET> at the questions asked in the program to determine
how the default answers can speed up your data entry process.

For a reliable <PRT SCREEN> copy of printed data insure that
GRAPHICS.COM is loaded prior to loading YAGIMAX.

EGA and VGA will probably require the monochrome versions to allow
<PRT SCREEN> to operate correctly. The color versions are much
nicer to look at on the CRT, however.

YAGIMAX will probably run on a computer without any graphics card,
but probably lockup if you try any graphics. Hercules users can
try the MSHERC.COM on this disk. It may work on some machines.
The shareware program HGCIBM.COM is now on the disk. Try it
using a /E switch to install CGA graphics capability on a Hercules
machine.

Some users of EGA have encountered problems using <PRT SCR> to
make a hard copy. It appears that placing the file EGAGRAF.COM
(included on this disk) in your AUTOEXEC.BAT file may clear up
this anomaly. The circles may come out somewhat eliptical, but
this also can usually be corrected in most modern printers using
a macro to reduce/increase line spacing prior to printing.

Should you want to add or subtract elements to a design, load the
design file as usual, at the MAIN MENU hit <ESC> to take you back to
the opening MENU. Select "New design" then enter the number of
elements you wish in the new design. Be sure and select the same
measurement system. i.e. "Inches/Inches" if that was the previous
design. Select the desired element diameter and at the new element
schedule simply enter the new length(s) and spacing(s), if you have
added new elements. The original numbers will be in memory. You
should probably save the new entry under a new filename prior to
proceeding.
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Currently, I am attempting to add the use a Microsoft Mouse with
YAGIMAX. This version (probably 2.22+) may be available early 1991.
Anyone who has previously received YAGIMAX direct from me who wishes
this version, drop me a card address below for the Information. When
available, I think $5.00 should cover the cost for disk, mailer, and
handling. Others who desire YAGIMAX plus the other goodies include
$8.00 for the complete set of files and programs.

If you enjoy these programs don't hesitate to send your cards and letters
(& donations!) to the following address:

Lew Gordon, K4VX
P.O. Box 105
Hannibal, MO 63401
[phone]
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