Below is a description of the input sequence in OMNEC.
Each input section reads data from INPUT.NEC, PARNR.NEC or from both files.
Below all lines of the test example 4x6 elements are described.
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INPUT:
CE 4x6 elements Not optimised
This is just a comment line. Like in NEC2 this line may be preceded by any
number of additional comment lines having CM as the first two characters.
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PARNR:
MO 1
This line tells OMNEC to use the modified wire radius when calculating matrix
elements for the interaction between wire segments and to use a more modern
value for the speed of light.
Alternative:
MO 0
Optimise with NEC2 in original form.
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PARNR:
GS 0 0 .001 .000 .000 .000 .000 .000 .000
This line has to be identical to the corresponding line in INPUT. It tells
that the dimensions have to be scaled by a factor 0.001 To convert from
millimetres to meters
Alternative:
GS 0 0 .02540000 .000 .000 .000 .000 .000 .000
To convert from inches to meters, so the antenna coordinates can be given in
inches.
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PARNR:
FR 0 1 0 0 .1441E+03 .0000 .0000 .0000 .0000 .0000
This line has to be identical to the corresponding line in INPUT. It tells,
exactly as in NEC2 what frequency to perform the calculation for.
Alternative:
FR 0 2 0 0 143.500 1.5000 .0000 .0000 .0000 .0000
Optimise for two frequencies at the same time. The first frequency is 143.5
and the second is 145.0 (increment=1.5). If more than one frequency is used
the sum of the sum of squares from all frequencies is minimised.
In this way the bandwidth should be improved. If more than one frequency is
used, the number of points in the radiation pattern may be limited.
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INPUT:
GW 1 5 .000 -495. 0. .000 495. 0. 5.000
PARNR:
GW 1 9 0 -1 0 0 1 0
These two lines specify the first wire.
cols 3-5 ITAG, specifies the wire by associating this number to
all segments that constitute this wire.
cols 6-10 NS, number of segments for this wire. The value in INPUT.NEC
is used, while the value in PARNR.NEC is not used at all.
cols 11-20 X1,INPUT=.000 the X coordinate of end 1 of this wire is 0
X1,PARNR=0 keep the X koordinate fixed.
cols 21-30 Y1,INPUT=-495. the Y coordinate of end 1 of this wire is -495
Y1,PARNR=-1 Optimise the Y coordinate. Increasing parameter
number 1 will cause element end 1 to move away from the element
midpoint.
cols 31-40 Z1,INPUT=.000 the Z coordinate of end 1 of this wire is 0
Z1,PARNR=0 keep the Z koordinate fixed.
cols 41-50 X2,INPUT=.000 the X coordinate of end 2 of this wire is 0
X2,PARNR=0 keep the X koordinate fixed.
cols 51-60 Y2,INPUT=495. the Y coordinate of end 2 of this wire is 495
Y2,PARNR=1 Optimise the Y coordinate. Increasing parameter
number 1 will cause element end 2 to move away from the element
midpoint.
cols 61-70 Z2,INPUT=.000 the Z coordinate of end 1 of this wire is 0
Z2,PARNR=0 keep the Z koordinate fixed.
cols 71-80 RAD, The wire radius.
The two ends of an element are changed in opposite directions in order to
keep the element centred on the boom.
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INPUT:
GW 2 5 .000 -460. 660. .000 460. 660. 5.000
PARNR:
GW 2 9 0 -2 3 0 2 3
Use parameter 2 to vary the length of wire 2, and use parameter 3 to vary
the Z coordinate for wire 2. Since radiation is maximised in the Z direction
this means that both length and position are optimised for this wire.
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INPUT:
GW 3 5 .000 -455. 1400. .000 455. 1400. 5.000
GW 4 5 .000 -450. 2000. .000 450. 2000. 5.000
GW 5 5 .000 -435. 3000. .000 435. 3000. 5.000
PARNR:
GW 3 9 0 -4 5 0 4 5
GW 4 9 0 -6 7 0 6 7
GW 5 9 0 -8 9 0 8 9
Associate parameters 4 to 9 to these 3 wires.
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INPUT:
GW 6 5 .000 -460. 3600. .000 460. 3600. 5.000
PARNR:
GW 6 9 0 -10 11 0 10 11
Optimise length an position for wire 6.
Alternative for PARNR:
GW 6 9 0 -10 0 0 10 0
Optimise length only for wire 6. This will cause an optimisation for a fixed
boom length of 3.600 meters.
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INPUT:
GM 0 0 .000 .000 .000 1700. 1800. .000 .000
PARNR:
GM 0 0 .000 .000 .000 12. 13. .000 .000
The antenna was placed with the midpoint of the reflector at the origin.
Move the whole structure 1700 millimetres in the X direction and
1.8 millimetres in the Y direction. Optimise the position for this antenna
by associating the parameters 12 and 13 to the X and Y shift respectively.
Causes optimisation of the stacking configuration in combination with
the GX option.
When optimising a single antenna, remove these lines and the GX line.
When optimising at a fixed stacking geometry, replace 12. and 13. in
PARNR.NEC by 0.
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INPUT:
GS 0 0 .00100000 .000 .000 .000 .000 .000 .000
Has to be identical to the GS line in PARNR, see above.
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INPUT:
GX100 110 .000 .000 .000 .000 .000 .000 .000
Reflection of structure in coordinate planes. This will create new wires
at the opposite side of the specified reflection plane(s). These new wires
will be numbered by adding the 100 (cols 3-5) to the ITAG value of the
original wires. Cols 8 to 10 specify the reflection planes. 110 means X and Y
but not Z.
First the structure, wires 1 to 6, is reflected along the X axis,
producing a new identical 6 element antenna with the centre of each element
at X=-1700 and Y=1800. The wires (elements) of this new antenna are numbered
201 to 206. Since the elements are along the Y axis the structure now
corresponds to two yagis stacked above each other at 3.4 meters distance.
Then the whole structure, wires 1-6 and 201-206, is reflected along the
Y-axis, producing two new antennas at the other side of the XZ plane so
the total structure becomes an array of 4 yagis at 3.4 vertical and 3.6
horizontal the new wires are numbered 201-206 and 301-306.
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INPUT:
GE 0 0 .000 .000 .000 .000 .000 .000 .000
End of structure section.
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INPUT:
FR 0 1 0 0 .1441E+03 .0000 .0000 .0000 .0000 .0000
Has to be identical to the corresponding line in PARNR.NEC, see above.
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INPUT:
EK 0 0 0 0 .0000E+00 .0000 .0000 .0000 .0000 .0000
Use the extended thin wire model of NEC2 (always do so!!)
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INPUT:
LD 5 1 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000
LD 5 2 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000
LD 5 3 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000
LD 5 4 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000
LD 5 5 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000
LD 5 6 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000
LD 5 101 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000
LD 5 102 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000
LD 5 103 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000
LD 5 104 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000
LD 5 105 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000
LD 5 106 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000
LD 5 201 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000
LD 5 202 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000
LD 5 203 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000
LD 5 204 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000
LD 5 205 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000
LD 5 206 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000
LD 5 301 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000
LD 5 302 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000
LD 5 303 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000
LD 5 304 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000
LD 5 305 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000
LD 5 306 0 0 .2701E+08 .0000 .0000 .0000 .0000 .0000
To account for ohmic losses, which is essential in optimising yagis, all
elements have to be loaded. The LD lines above specify aluminium as the
element material. There are more options for LD - refer to the NEC2 manual.
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INPUT:
KH 0 0 0 0 .1500E+01 .0000 .0000 .0000 .0000 .0000
Use a simplified field approximation at segment separations
above 1.5 wavelengths.
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INPUT:
EX 0 2 3 0 .1000E+01 .0000 .0000 .0000 .0000 .0000
PARNR:
EX 0 2 5 00 50 0 0.05
Specify feed point.
cols 3-5 Type of excitation 0=Voltage source (applied-E-field source)
5=Voltage source (current-slope-discontinuity)
The other modes available in NEC2 are illegal in OMNEC
cols 6-10 Number of wire to feed. The number has to be the same in both
inputs and here 2 specifies the wire with ITAG=2 to be a radiator.
cols 11-15 Segment number for segment to feed. The number is taken from
INPUT.NEC while the number in PARNR.NEC is ignored. If this
number = (NS+1)/2 the element is fed at its centre. Here with
NS=5 (see above, GW 2 ...) the centre point is on segment 3.
cols 21-30 INPUT: Real part of applied feed voltage.
PARNR: Desired value for real part of feed impedance
cols 31-40 Imaginary part of feed voltage.
PARNR: Desired value for imaginary part of feed impedance
cols 41-50 ZWEI, a weight factor giving the weight for the impedance error
equation in the total least squares problem. Large values
give impedances close to the desired value even if the cost is
high in gain, while small values will give the desired impedance
only if it can be obtained at a marginal loss of gain.
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INPUT:
EX 0 102 3 0 -.1000E+01 .0000 .0000 .0000 .0000 .0000
EX 0 202 3 0 .1000E+01 .0000 .0000 .0000 .0000 .0000
EX 0 302 3 0 -.1000E+01 .0000 .0000 .0000 .0000 .0000
PARNR:
EX 0 102 0 00 50 0 0
EX 0 202 0 00 50 0 0
EX 0 302 0 00 50 0 0
Note that all image antennas have to be properly fed. When an antenna is
reflected along the Y axis, the direction of the elements change sign so
in order to be properly phased, these antennas have to be fed with
a 180 degrees phase shift.
Since the feed impedance is identical for identical antennas, there is
no reason to include more equations doing the same thing. Therefore
cols 41-50 is 0.
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INPUT:
RP 0 12 60 0 .9000E+02 .0000 .0004 .0003 .0000 .0000
Calculate radiation pattern. This line allows a compromise between computing
speed and accuracy. The optimisation is done by a simultaneous minimisation
of the power radiated in all directions except forward. The directions for
which the field is calculated are controlled by the stepping parameters of
this line.
cols 3-5 NPPRT, a parameter to control radiation pattern listed in
output file PATTERN.NEC.
NPPRT=0 No radiation pattern in output.
NPPRT=1 Pattern with theta=0, phi is stepped.
NPPRT=2 Complete pattern, phi and thete stepped.
NPPRT=3 Integrated pattern: Power radiated from 0 to
phi (integrated over theta) as a function of phi.
cols 6-10 NTH is the number of values of theta. Theta is a rotation
around the Z-axis, and for a single yagi very few points are
needed. For a stacking configuration like in this example, more
points are needed.
cols 11-15 NPH is the number of values for phi, the angle to the forward
direction. phi=0 means forward and phi=180 degrees is backwards.
cols 21-30 Largest value for theta. For a symmetric antenna there is no
need to turn more than 90 degrees on theta. Continuing up to
360 degrees will just repeat the lobe pattern which does not
help the optimisation. In this example the radiation pattern is
calculated in 12 directions. The step size is 90/12=7.5 degrees
and the radiated power is calculated with theta=3.75, 11.25,
18.75,.....,86.25
cols 31-40 Start value for phi. If this value is not 0, the summation
excludes points near the forward direction, and the gain as
calculated by integration becomes incorrect. The optimisation
results in a broader main lobe and better suppression of the
lobes above the start value. Do not use large numbers here.
Try points on the main lobe of the initial structure.
cols 41-50 GOVERT, a parameter putting more weight on the least squares
equations above 30 degrees in phi. Large values should improve
lobe suppression above 30 degrees at the expense of gain. By
variation of this parameter it should be possible to find optimum
G/T (?).
cols 51-60 EFFWEI, a weight factor on an equation in the least squares fit
for ohmic losses. With this parameter lower losses are obtained
at the expense of gain. Lower losses means less current so this
parameter tends to reduce Q and thereby it improves bandwidth.
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INPUT:
EN
The last line - an end mark.
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