Good Evening,
It was a cool week with some fog, then a thunderstorm with an inch
of rain. The forest enjoyed the moisture. Some of the ferns are
turning yellow from a few 30 degree nights. Smoke has returned but not
as thick as it was last week.
The sun continues to be moderately active with no X class flares
predicted. Solar flux is still high, it is simply less unsteady.
Nonetheless, there should be QSB and some hissing. The sun is rapidly
moving southward. Sunset is at 8:02 PM, forty minutes earlier than at
the beginning of August.
I posted the code necessary to calculate the electric field around a
1/2 wavelength dipole antenna. It will be used to create 3D mesh models
of antenna radiation patterns; then animate them as the user changes any
one of seven variables. I have similar code for 1/4 wave verticals and
1/2 wave loop antennas. Animating antenna radiation patterns should be
fun, the UI building less so :)
Please join us on (or near):
14050 kHz at 2200z Sunday (3 PM PDT Sunday)
7047 kHz at 0000z Monday (5 PM PDT Sunday)
73,
Kevin. KD5ONS
-
// dipole.c
// K. J. Rock
// August 25, 2023
// g++ -o dip dipole.c
#include <stdio.h>
#include <math.h>
#define ETA 376.991118308 // characteristic impedance of
free space
#define RAD 0.017453293 // radian to degree
#define PI 3.1415926535 // cherry, of course
#define TWOPI 6.28318530718 // Katzenjammer feast
#define PIOVR2 1.57079632679 // slipped from sill
int main( void )
{
float f = 100; // frequency in MHz
float lambda = 300 / f; // wavelength in meters
float l = lambda / 2; // length of antenna
in meters
float k = TWOPI / lambda; // save some space
float h = 1.0; // height of
antenna in wavelengths
float I0 = 2; // maximum
current in amperes
float r = 1000; // distance from
antenna to observer in meters
float dTheta = 20.0; // azimuth step size
float dPhi = 5.0; // elevation step size
float scale = 1.0; // fudge factor
for display purposes
for (float theta=0; theta<180; theta += dTheta) // azimuth
{
for (float phi=0; phi<360; phi += dPhi) // elevation
{
float radius = scale * (ETA * k * I0 * l * sin(k * r)
* sqrt(1 - sin(theta*RAD-PIOVR2) * sin(theta*RAD-PIOVR2) *
sin(phi*RAD) * sin(phi*RAD))
* sin(k * h * cos(theta * RAD-PIOVR2))) / (TWOPI * r);
printf("%7.4f ", radius ); // E(θ,φ) in
Volt/meter or Newton/Coulomb
}
printf("\n");
}
return 0;
}
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