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XNECVIEW(1)		    General Commands Manual		   XNECVIEW(1)

       xnecview	- A program for	visualizing NEC2 input and output files

       xnecview	[options] filename [filename....]

       Xnecview	 can visualize NEC2 input (structure of	the antenna model) and
       output data files (gain as a function of	direction, gain	and  impedance
       as  a function of frequency).  Structure	and gain are shown as a	three-
       dimensional picture which can be	rotated	by  the	 mouse.	  The  program
       will  determine the type	of data	(input or output) from the files them-

       More information	and some examples can be found on the web at

       On the commandline, the program expects to find one or more  filenames,
       each containing either NEC2 structure (input) data, or output data (im-
       pedance and radiation pattern).	The program will determine the type of
       data  from the data itself.  Depending on the data found	in the file(s)
       specified, one or two windows are opened.  Window 1 shows a 3D plot  of
       the structure (wires etc.) of the antenna, and/or the spatial distribu-
       tion of the radiation.  Window 2	shows a	set of graphs of several quan-
       tities (SWR, gain, etc.)	 as a function of frequency.

   Window 1
       This  window  shows  the	 antenna's  structure and/or the gain pattern.
       Initially, the Z	axis points up,	the X axis points to lower  left,  and
       the  Y axis points to lower right (unless you changed those settings in
       the source code).

       The view	can be manipulated using the mouse as follows:

       rotate move mouse while holding left  button  depressed	(additionally,
	      keep  CTRL  depressed  to	drag only a partial picture for	higher

       zoom   move mouse up/down while holding middle button depressed	(addi-
	      tionally,	keep CTRL depressed to drag only a partial picture for
	      higher speed); alternatively, click left mouse button for	 zoom-
	      ing in or	click right mouse button for zooming out.

       move picture
	      move  mouse  while holding right button depressed	(additionally,
	      keep CTRL	depressed to drag only a partial  picture  for	higher

       go back to original view
	      click middle mouse button

       The view	can also be rotated using the arrow keys.  The keys PageUp and
       PageDown	select a different frequency, if radiation data	 is  available
       at more than one	frequency.

       The  top	 of the	window contains	a set of buttons and other indicators;
       from left to right these	are:

       quit   to stop the program; keyboard shortcut: Q

       reload to reload	the files; keyboard shortcuts: R and .

       export for saving the picture as	an (encapsulated) PostScript or	a  PNG

	      toggles  displaying  of antenna structure	on and off; in '+tags'
	      mode, segment tag	numbers	are displayed too (which can be	 help-
	      ful when trying to modify	an antenna structure).	For display of
	      currents and animations, see below.

	      toggles display of gain pattern: either none is shown,  or  only
	      slices  in the coordinate	planes,	or the entire 3D structure (of
	      course subject to	the availability of data in NEC's output file,
	      and  thus	 ultimately  to	 the RP	cards used in the input	file).
	      The 3D structure can either be  shown  as	 a  wire  mesh	(i.e.,
	      transparent),  or	 as an opaque surface (i.e., with hidden lines
	      removed);	the latter usually gives a clearer picture, but	is of-
	      ten somewhat slower, and is not available	if the NEC output data
	      do not cover a theta range from 0	to 90 or 180  degrees,	and  a
	      phi  range  from 0 to between 270	and 360	degrees; note that the
	      gain surface is only opaque w.r.t. itself, not to	other elements
	      of  the  picture	such as	the antenna structure.	For display of
	      near fields, see under 'animation' below.

	      toggles gain scaling (linear in power, linear in voltage,	 ARRL-
	      style, or	logarithmic with -40 dB	at the center).

	      determines the handling of radiation's polarization: whether the
	      gain shown is according to the total power regardless of	polar-
	      ization,	 or   only  the	 horizontal/vertical/left-hand	circu-
	      lar/right-hand circular component.  Choosing "colour" also shows
	      the  total  power, but uses colour to show whether the radiation
	      is mostly	linearly polarized, or lhcp  or	 rhcp.	 This  setting
	      also influences the gain-vs-frequency plots in window 2, and the
	      currents display in window 1 (see	below).

       X, Y and	Z
	      rotate view to viewing along X, Y	or  Z  axis  respectively.   A
	      gain  scale will appear, with lines at several gain levels.  All
	      of these gains are with respect to the maximum gain in  the  en-
	      tire set of output data.

       Though  xnecview	 should	be quite liberal in accepting output data from
       NEC, you	might want to start out	by using this line (card) in your  in-
       RP 0, 37, 72, 1000, 0, 0, 5, 5
       This will instruct NEC to calculate the gain at 5 degree	intervals.

   Window 2:
       This  window contains plots of several quantities as a function of fre-
       quency, if the NEC output file contains data for	 several  frequencies.
       The following quantities	can be plotted:


       real and	imaginary part of the input impedance

       phase and magnitude of the input	impedance
	      If  the antenna has multiple sources, SWR	and impedance are only
	      plotted for whichever source's data appears first	in the	output

       maximum gain and	corresponding front/back ratio
	      The gain as plotted is the maximum gain observed over the	entire
	      radiation	pattern; this may not be the direction	in  which  the
	      antenna  was  supposed  to radiate! The front/back ratio is just
	      the ratio	of the maximum observed	gain to	the gain  in  the  ex-
	      actly  opposite direction; again,	this may not be	the front/back
	      ratio you're interested in, e.g. if the main lobe	is elevated so
	      the 'back' direction points into the ground.

	      If  a  specific  polarization (rather than total power) has been
	      chosen (by command-line option or	by the button in the  top  row
	      of  window  1),  this also influences the	graph.	Two gain lines
	      then appear: a solid line	showing	the gain in the	 selected  po-
	      larization,  and	a dashed line showing the total	gain (for com-
	      parison).	 Also, two f/b lines appear: for both, the front power
	      is  only	the  selected  polarization  component,	while the back
	      power is also the	selected polarization (solid line), or the to-
	      tal power	(dashed	line).

       direction (phi and theta) of maximum gain

       vgain and corresponding front/back ratio
	      This  is the gain	in the direction towards viewer	(as set	by ro-
	      tating the picture in window 1) and the corresponding front/back

       The row of buttons at the top have the following	functions:

       quit   to stop the program; keyboard shortcut: Q

       reload to reload	the files; keyboard shortcuts: R and .

       export for  saving the picture as an (encapsulated) PostScript or a PNG

       Z0=... for setting the reference	impedance for SWR  calculations;  fur-
	      thermore,	the impedance plots are	limited	to 20*Z0.

       maxgain,	vgain, SWR, Re/Im, phi/abs, and	dir
	      for toggling the display of the graphs.

       Finally,	 if  radiation pattern data is available, a vertical line over
       the entire height of the	window shows the frequency at which the	radia-
       tion  pattern is	being shown in the other window. With a	mouse click or
       drag, or	the keys PageUp, PageDown and arrow  keys,  another  frequency
       can be chosen.

   Display of current distribution:
       Window  1  can  also be used to display the distribution	of the current
       flowing in the antenna wires, if	this information is available  in  the
       NEC  output file(s); by default,	it is, but it may be switched off by a
       'PT' card in the	NEC input.  This display is enabled by selecting 'cur-
       rents'  in  the none/struct/+tags/currents menu.	 Then the thickness of
       each wire segment indicates the magnitude of the	current	flowing	there,
       while  the  colour  indicates its phase.	 At the	bottom of the window a
       few extra controls appear: two sliders for  changing  the  colours  and
       scaling the thicknesses,	and some buttons which are discussed below.

       Contrary	to what	might be expected, the magnitude and phase of the cur-
       rent as plotted are not necessarily directly the	values present in  the
       NEC  output file.  Taking that data directly would typically not	result
       in a meaningful display,	since there is a 180 degree  phase  ambiguity:
       if the endpoints	of a wire are exchanged, then the 'positive direction'
       in that wire is reversed, so the	phase calculated by NEC	changes	by 180
       degrees	even  though  the  antenna  and	 its  properties don't change.
       Therefore, it is	preferable to project the current in each segment onto
       some  reference	direction,  e.g., horizontal.  The result of this is a
       measure for the contribution of that segment to the horizontally	polar-
       ized  radiation of the antenna.	The polarization actually used,	is the
       one selected by the polarization	button in the top row;	choosing  "to-
       tal"  there  (default), switches	the projection operation off, so 'raw'
       phases and magnitudes are used.	If left- or right-hand circular	polar-
       ization	is  selected,  the projection is also not performed, but every
       current gets an extra phase shift proportional to the angle its projec-
       tion perpendicular to the viewing direction makes with horizontal.

       Actually,  the phase displayed as discussed above is still not very in-
       teresting.  Consider the	following: if one segment is further away from
       the  target  to	which  the antenna is supposed to radiate than another
       segment,	then the radiation from	the former segment will	incur a	larger
       delay  before  reaching	the  target than the radiation from the	latter
       segment.	 Effectively, this introduces another phase-shift, whose value
       depends on the position of the segments in space.  Xnecview can compen-
       sate for	this effect, by	calculating this additional phase-shift	in the
       direction  toward  the viewer (i.e., perpendicular to the screen); this
       option can be switched on and off by the	first  button  on  the	bottom

       The  second button locks	the direction used in the phase-shift calcula-
       tion; its use can best be explained by an example.  Consider a yagi an-
       tenna  which  is	aimed along the	X axis.	 Then in order to get the cor-
       rect phase-shift, one needs to rotate the picture such that the X  axis
       points  to the viewer.  Unfortunately, in that orientation all elements
       are behind each other, so it is impossible to distinguish them in order
       to  compare  their  colours.   This problem is resolved by pressing the
       'lock' button to	lock the phase-shift calculation and then rotating the
       antenna to an orientation in which the elements are distinguishable.

   Animated display of currents, charges and near fields:
       Antennas	 as  modeled  by NEC are driven	by a source (or	more than one)
       which applies a voltage or current to the antenna, varying sinusoidally
       in  time.  Consequently,	the currents in	the antenna wires, the charges
       on the wires, and also the electric and magnetic	field in the surround-
       ing  space, vary	sinusoidally in	time too, at the same frequency	as the
       driving force, but possibly with	a different phase.  The	display	of the
       currents	 as  described	in the previous	section	represents these time-
       varying currents	by their amplitude  (thickness	in  the	 picture)  and
       phase w.r.t. the	source (colour in the picture).

       For some	purposes, this is not very intuitive.  Therefore, xnecview can
       also show the currents (and charges and	field  strengths)  exactly  as
       they vary in time: an animation.	 Basically, the	process	which in real-
       ity happens at a	frequency of thousands or more cycles  per  second  is
       slowed  down  to	 a  frequency of about 1 cycle per second, and at that
       speed the currents and charges are displayed.

       The animated display of currents	and charges is	enabled	 by  selecting
       'animation'  from  the none/struct/+tags/currents/animation menu.  Then
       each segment of each wire is replaced by	a short	blue line, one end  of
       which  is  at the center	of the wire, while the other end indicates the
       direction and (relative)	magnitude of the current.  Furthermore,	around
       each segment a square is	drawn. This square represents the charge built
       up on that segment.  The	size of	the square is proportional to the mag-
       nitude  of  the charge, while the colour	shows the sign:	cyan for posi-
       tive charge, magenta for	negative.

       The animated display of the electric and	magnetic field	near  the  an-
       tenna  is  chosen  by  selecting	 'near'	from the none/slice/frame/near
       menu.  Then at every point for which near field data is	found  in  the
       NEC  output  file, three	coloured lines (vectors) are drawn.  A red one
       indicates the direction and (relative) magnitude	of the electric	field,
       and a green one indicates the direction and (relative) magnitude	of the
       magnetic	field.	From the electric and magnetic field vectors, the  so-
       called  Poynting	 vector	 is  calculated, and displayed in yellow. This
       vector can be interpreted as the	flow of	 energy;  see  a  textbook  on
       electromagnetic theory for details.

       When either or both of the animated displays is selected, an additional
       set of controls appears at the bottom of	the window.  The left four  of
       these  are  sliders to control the scaling of (from left	to right) cur-
       rents, charges, electric	and magnetic field strength.  To the right  of
       these,  an on/off control labelled 'P' is shown,	which controls whether
       or not the Poynting vectors are drawn.  The rightmost  slider  controls
       the speed of the	animation: if your computer is fast enough, the	number
       at the slider is	the number of animated cycles per second.  By  setting
       this  slider to 0, or hitting the 'z' key, the animation	can be frozen.
       Then the	phase can be changed back and forth by typing '<' and  '>'  on
       the keyboard.

       Obviously,  xnecview can	only show currents, charges and	near fields if
       such information	is available in	the NEC	output file being  visualized.
       As  discussed earlier in	this manual, the inclusion of currents is con-
       trolled by the PT card in the NEC input.	 The inclusion of  charge  in-
       formation  is  controlled  by  the PQ card, and the calculation of near
       electric	and magnetic fields is controlled by NE	and NH cards,  respec-
       tively.	Examples are:
       PQ  0,  0
       NE  0,  1,20,20,	 0,0.05,0.05,  0,0.05,0.05
       NH  0,  1,20,20,	 0,0.05,0.05,  0,0.05,0.05
       These  instruct NEC to include the charge information, and to calculate
       the near	fields at 20 x 20 points in a grid with	stepsize 0.05, in  the
       Y-Z-plane.  For more information	see NEC	documentation.

       In normal usage of xnecview, command-line options (other	than the names
       of the files to be displayed) are rarely	needed.	 However, they can  be
       useful  to  bring  xnecview  quickly  in	 the  desired state, or	to use
       xnecview	for non-interactive, automated generation of plots.

       Command-line options can	not only be given on  the  command  line  with
       which  xnecview	is started, but	they can also be embedded as a CM card
       (line) in the NEC input file to be read.	 In order for the content of a
       CM  card	 to be recognized as xnecview options, the CM card should con-
       tain the	word xnecview: (including the colon) before those options.

       The following options are available:

       -h, --help
	      show usage information

	      set structure view to 'struct'

       --tags set structure view to 'struct+tags'

	      set structure view to 'currents'

	      set structure view to 'animation'

	      set radiation view to 'slice'

	      set radiation view to 'frame'

	      set radiation view to 'opaque'

       --near set radiation view to 'near field'

	      set radiation scale linear in power

	      set radiation scale linear in voltage

       --arrl set radiation scale to ARRL style

       --log  set radiation scale to logarithmic

	      choose polarization; x may be total, hor,	vert,  lhcp,  rhcp  or
	      colour .

       --qscale	num
	      set charges scale	(animation)

       --iscale	num
	      set currents scale (animation)

       --escale	num
	      set electric field scale

       --hscale	num
	      set magnetic field scale

	      hide Poynting vector in near field display

       --afreq num
	      set animation frequency (Hz)

       --aphase	num
	      set animation phase (degrees)

       --aupdate num
	      set  animation  update  interval (milliseconds). Default is 100,
	      but on a slow computer and/or with a large data set  it  may  be
	      useful to	set the	update interval	higher.	 Conversely, on	a fast
	      computer and with	a simple data set, a smaller setting  provides
	      smoother movement.

       --freq num
	      set frequency (MHz)

       --z0 num
	      set reference impedance (ohm)

       --expeps	filename
	      no X11 display, just export picture to .eps-file

	      no X11 display, just export picture to .png-file (only available
	      if linked	against	the libpng library)

       --view phi,theta,zoom,trx,try
	      set viewing direction and	zoom

       Note: typing 'v'	in window 1 writes the current values for all of these
       settings	to the standard	output.

       Pieter-Tjerk   de  Boer;	 Internet  e-mail:,  amateur
       packet-radio: PA3FWM @ PI8DAZ.#TWE.NLD.EU.



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