Ham Radio 2000/Ham Radio 2000.iso/ham2000/antenna/yagiopt/plot.doc

Text File | 1988-11-02 | 13KB | 266 lines

               Antenna Plotting Program



    PLOT.EXE will plot far-field antenna radiation patterns directly on
your graphics screen.  The patterns may be generated by the MN general-purpose
antenna analysis program or by the special-purpose YO Yagi Optimizer program.
Azimuth and elevation patterns are plotted, using either polar or rectangular
coordinates.  PLOT will work with a Color Graphics Adapter, Enhanced Graphics
Adapter, or Hercules Graphics Card.  You can execute PLOT by itself to view
plots made previously, or you can use the P command while running MN, or the H
command while running YO.  These commands automatically generate a plot file
for the antenna under analysis, call PLOT to display the plot, and then return
to MN or YO when you are done.

    If you are using an EGA or HGC, a second plot file may be selected for
pattern comparison.  The new plot is drawn into the second graphics buffer, and
the screens may be switched back and forth instantly with a single key stroke,
without having to wait for the plots to be redrawn.  This permits a precise
instantaneous pattern comparison, revealing effects of small changes in an
antenna design that would not be noticed in a side by side comparison of
printed plots.  Either of the antenna plots may be replaced by a third, and so
on, allowing multiway comparisons two at a time.  This feature is not available
for the CGA because it lacks a second graphics buffer.


                Running PLOT


    To run PLOT do the following, according to your display type:

 HGC:    The HERCULES.COM graphics driver must be loaded before
     plotting.  To do this simply execute HERCULES.  This needs
     to be done only once per boot, so HERCULES may be put in
     your AUTOEXEC.BAT file for convenience.

 CGA:    Load GRAFTABL and GRAPHICS once per boot (or put them in
     your AUTOEXEC.BAT file).  These are standard DOS programs.
     They will improve the CGA graphics characters and allow
     you to transfer the CGA plots to your printer.

 EGA:    The EGA requires no preliminaries.


    When executed, PLOT automatically determines which type of graphics
display card is present, and then configures itself accordingly.  The PLOT
features vary according to the display type.

    You may give the name of the plot file on the command line when
invoking PLOT, otherwise you will be prompted for it.  You need not type the
.PLT extension, it will be provided automatically.

    The following keys are active in various modes during the plot:

 <Enter>    Switch between azimuth and elevation plots
    P        Switch between polar and rectangular
         coordinates
    L        Switch the polar plot scale between log dB
         and linear dB
    Y        Change the rectangular plot Y-axis gain cutoff
    N        Normalize the plot of the lower-gain antenna
         to the gain scale of the higher-gain antenna;
         pressing again reverts to normal
    A        Select another antenna and turn off plot
         compare mode
    C        Select another antenna and use plot compare
         mode (not for CGA)
 <Space>     Switch between two comparison plots
         (not for CGA)
   1-6        Change display colors (EGA only)
    S        Save display colors (EGA only)
 <PrtSc>    Print screen (Press <Shift><PrtSc> or
         <Shift><F10>)
  <Esc>        Exit the plot program
   F1        Activate the help panel, an abbreviated
         version of this list

    The help panel only lists keys which are active at the time the F1 key
is pressed.  For example, the Y key is only listed when in rectangular mode.
Similarly the N, S, C, <Space>, and 1-6 keys are never listed for the CGA,
since the CGA hardware cannot handle these functions.

    The A command will turn off compare mode, enabling you to examine the
patterns of single antennas more rapidly.  Also note that the C command can be
used repeatedly to compare multiple antennas two at a time.

    Whenever you are prompted for a plot filename you may press <Enter> to
obtain a listing of the available plot files.


                Polar Plots


    The azimuth polar plot is displayed with the MN +X direction toward the
top of the screen, and the +Y direction to the left.  Zero azimuth angle is at
the top of the screen, 90 degrees is to the left, 180 is at the bottom, and 270
is to the right.  Elevation plots have the +Z direction (overhead) at the top
of the screen, and the +X axis to the right.  Unidirectional antennas, if aimed
in the +X direction, will have their major lobe pointing upward on the azimuth
plot, and toward the right on the elevation plot.  This arrangement allows you
to distinguish azimuth plots from elevation plots at a glance.

    You may select either of two radial scales for a polar plot. The
standard ARRL log dB scale causes lower level sidelobes to be compressed toward
the center of the pattern, emphasizing the major lobe shape.  Almost all
antenna patterns in amateur radio publications use this scale, so it provides a
way to compare the antennas you develop using MN to existing designs.  It also
produces patterns having familiar shapes.  The center of the plot is minus
infinity dB (no signal) with this scale, but there is little plot area below
-40 dB.  The other polar scale is a linear dB scale, with -50 dB at the center
of the plot, and much more area for signals between -20 and -50 dB than the log
dB scale.  This scale is useful for examining small sidelobes which are hard to
see in a log dB plot.

    The dots forming the radial lines (the ones which are not multiples of
30 degrees) are spaced every 2 dB.  The dots forming the circles are spaced at
multiples of 1 degree.  These calibrations allow you to read directivity values
off the antenna pattern with good accuracy.  Using them you may never need to
use the MN D command to generate tabulated pattern data in a RUN file.

    If the antenna is in free-space PLOT will draw a 360 degree elevation
polar plot.  If it is over ground only the upper 180 degree hemisphere is
shown.

    To save time, MN normally generates data only for 0 to 180 degrees in
azimuth, and 0 to 180 degrees (the overhead half plane) in elevation.  YO
always generates such data.  In this case PLOT assumes symmetry around the X
axis, and draws the right half of the azimuth plot from the data for the left
half.  Similarly, for free-space antennas the lower half of the elevation plot
simply duplicates the pattern of the upper half.  However, for asymmetrical
antennas you can force MN to generate data for the entire 360 degree plane by
using "360" as a parameter when entering the G command to MN.  Both azimuth and
elevation data will be generated for 360 degrees (elevation data will cover 180
degrees if the antenna is not in free-space).

    The polar plots will be perfectly circular on a monitor adjusted for
normal aspect ratio.  If they look elliptical you should adjust your vertical
height control.  This control is located on the rear panel of most monitors.


                  Rectangular Plots


    Rectangular or X-Y plots may be selected with the P command.  This
coordinate system reveals small sidelobe detail even better than the linear dB
polar plot, but the overall shape of the pattern is lost.  The X-axis is
azimuth or elevation angle from 0 to 180 or 360 degrees, and the Y-axis is the
antenna response in dB using a linear scale.  The Y-axis cutoff, or lower limit
in dB, may be changed using the Y command.  Because this parameter is always a
negative number, you may enter it without the minus sign for convenience.  The
Y-axis cutoff is constrained between -1 and -100 dB.  The Y-axis is easiest to
interpret when the cutoff value is a multiple of 10 degrees, but you may enter
any value and the scale and grid will be drawn correctly.  The horizontal grid
lines have dots every 2 or 4 degrees.  The vertical grid lines have dots every
.02, .1, .25, .5, 1, or 2 dB depending on the Y-axis cutoff value.  The X-axis
is 180 degrees wide unless the plot file contains independent data for the
whole 360 degree plane.


               Plotting While in MN


    MN generates a plot file whenever you enter the P command, and then
calls PLOT.  The root name of the plot file will be the same as that of the
current antenna file, with the extension .PLT.  When experimenting with an
antenna you may wish to save more than one plot file, either for later
examination or for immediate comparison using the plot compare feature.  To
generate a plot file with a new name simply append the name as a parameter to
the P command.  The .PLT extension need not be typed as MN will add it
automatically.

    If you are only interested in viewing the azimuth response you need not
wait for the elevation data generation to complete after entering the P
command.  Simply press <Esc> to abort the elevation search, and the azimuth
plot will appear.  The plot file will only contain azimuth data, but will
otherwise plot normally.  You may later enter P, wait for the elevation search
to complete, and MN will add the elevation data to the existing plot file.

    Adding the parameter "360" to the G command will cause the azimuth and
elevation data to be generated for the entire 360 degree plane.  This is useful
for plotting the response of asymmetrical antennas, such as wire antennas
erected to take advantage of randomly positioned tall trees.  A subsequent P
command, after a "G 360", will generate the plot file, and call PLOT.

    Some highly-directive antennas will plot better if data is generated
every 1 degree instead of the usual 2 degrees.  To cause this use the parameter
"1" with the G command.  This parameter may be used at the same time as the
"360" parameter.  Parameter order and spacing are not important as MN just
looks for a "1" and a "360" somewhere on the G command line.  These parameters
are not available with the P command to avoid confusion with the P parameter
that renames plot files.  To plot with the "360" and "1" parameters, do G first
with the parameters, then P.

    Plot data is generated with a dynamic range of 100 dB and with a
resolution of .01 dB.  The elevation angle is annotated on azimuth plots only
if it is nonzero, and the same holds for the azimuth angle on elevation plots.


                  Plotting While in YO


    YO generates a plot file whenever the H key is pressed, and then calls
PLOT to display the pattern.  YO generates free-space plots with 1 degree
resolution for Yagis having 15 or more elements, and plots with 2 degree
resolution for smaller antennas.


               DOS Environment Variables for PLOT


    You may tell PLOT to display gains in dBi rather than dBd by using the
following DOS command:

    SET DB=dBi

    Any combination of upper and lower case letters can be used.

    To specify a directory to be used as a plot library do the following:

    SET PLTLIB=Directory

    PLOT will list the plot files in this directory and those in the
current directory when started without a filename on the command line.  You may
load a plot file from the plot library by simply entering the filename, the
directory need not be given.  This also applies if you specify the plot
filename as a command line parameter when invoking PLOT.  For more information
on SET commands see MN.DOC or YO.DOC.


                  EGA Colors


    Keys 1 through 6 will change the screen colors while you are viewing
the EGA display.  After selecting the colors you prefer, you may save the
changes by pressing the S key.  The color codes will be saved in the file
COLORS.EGA.  When you next run PLOT the saved color set will be read back in.
If COLORS.EGA is not found PLOT will use bright white on a black background for
everything.

    The color keys are:

         1    Background color
         2    Antenna pattern color
         3    Grid color
         4    Grid label color
          5    Annotation color
         6    Help panel color


            Making Hardcopies of Plot Screens


    You may press <Shift><PrtSc> to print the current screen.  On some
keyboards PLOT may not recognize the key marked PrtSc.  If this is the case you
may use <Shift><F10> instead.  It is normal for the polar plots to come out
somewhat elliptical on paper.  For the EGA and HGC, if you start the first plot
at the top of the page, a second plot may be put on the same page without any
manual realignment of the printhead.  Simply call up the second plot and press
<Shift><PrtSc> again.  This is a nice way to save both the azimuth and
elevation plots for a single antenna, or to compare two antennas.  PLOT does
not respond to <Shift><PrtSc> or <Shift><F10> with the CGA, or perform any
printing function.  Instead, DOS will intercept <Shift><PrtSc> and print your
plot if GRAPHICS was loaded before starting PLOT.