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/* From the feeble mind of N3GO - Gary O'Neil - March 17, 1995 */
/* End-fed Zepp/J-pole design calculations */
/* */
/* Converted from BASIC to C by SM5SXL Mats Petersson 950407 */
/* Ncurses conversion 970319 */

#include <config.h>
#include <stdio.h>
#ifdef STDC_HEADERS
# include <stdlib.h>
#endif
#include <math.h>

input(char *p, double *v)
{
printf("%s", p);
while (! scanf(" %lf", v))
getchar();
}

design()
{
/* ZA = Antenna Feedpoint Impedance, ZF = Feedline Impedance, and */
/* Z0 = the impedance of the matching transmission line. */
/* ZA = 3500 to 5000 ohms for end fed dipole. */
/* ZF = 50 ohms in my analysis */
/* Z0 = 300 Ohms nominal ** Note: Maximum = sqrt(ZA*ZF) */

double za, z0, zf, zmax, zp, rho, yf, b, l1, l2, x1, x2, dipole, series,
shunt, r,f,v;
static char fs[21], vs[21];
char tmp[82];

za = 5000;
zf = 50;
z0 = 300;

zmax = sqrt(za * zf);
if (z0 > zmax) goto errexit;

printf("\nFeedline Impedance (Ohms): %.0f\n",zf);
printf("Matching Transmission line Impedance: %.0f\n",z0);
input("\nFrequency (MHz): ", &f);

/* V = velocity factor of transmission line used for matching network */

input("\nVelocity factor: ", &v);

while (1) {
/* ZP = the antenna impedance ZA normalized to the stub impedance Z0 */

zp = za/z0; /* Equation A1 */

/* RHO = the antenna reflection coefficient with respect to the matching
stub impedance */

rho = (zp-1)/(zp+1); /* Equation A2 */

/* YF = the feedline admittance 1/ZF normalized to the stub admittance 1/Z0 */

yf = z0/zf; /* Equation A3 */

/* B = the normalized susceptance of the shorted stub section */

b = sqrt((pow(rho,5) * pow(yf+1,2) - pow(yf-1,2)) /
(1-pow(rho,2))); /* Equation A4 */

/* X2 = the normalized reactance of the shorted stub section */

x2 = 1/b; /* Equation A5 */
l2 = atan(x2) * (180/M_PI); /* Equation A6 */
r = yf/(pow(yf,2)+pow(b,2)); /* Equation A7 (Real) */
x1 = b/(pow(yf,2)+pow(b,2)); /* Equation A8 (Imag) */
l1 = 90 - (atan(x1) * (180/M_PI));

/* The constant 5606 is 95 per cent of the speed of light in inches
for a half wavelength at 1 MHz */

dipole = 5606 / f; /* Equation A9 - A */

/* The constant 32.78 is the speed of light in inches/degree/MHz */

series = 32.78 * v * (l1/f); /* Equation A9 - B */
shunt = 32.78 * v * (l2/f); /* Equation A9 - C */

printf("\nFrequency in MHz = %f\n",f);
printf("Wavelength in air = %f cm\n",(299.7*39.37/f) * 2.54);
printf("Length of stub = %f wavelengths\n",(l1+l2)/360);
printf("Height of 'Tap' = %f wavelengths\n",l2/360);
printf("Dipole Length = %f cm\n",dipole * 2.54);
printf("Series Trans. Line = %f cm\n",series * 2.54);
printf("Shunt Trans. Line = %f cm\n",shunt * 2.54);
printf("Stub Length = %f cm\n",series * 2.54 + shunt * 2.54);
printf("Overall Length = %f cm\n",series * 2.54 + shunt * 2.54 + dipole * 2.54);
printf("\n");
printf("Impedances used for this calculation are as follows:\n\n");
printf("Impedance of End-fed Dipole: %.0f Ohms\n",za);
printf("Antenna System Feedline Impedance: %.0f Ohms\n",zf);
printf("Matching Section Transmission line Impedance: %.0f Ohms\n",z0);
printf("Maximum Usable Matching line Impedance: %.0f Ohms\n",zmax);
printf("Velocity Factor of Matching Section: %f\n",v);
input("\nNew Velocity factor (enter zero to quit): ", &v);
if (v == 0) return;
}

errexit:
printf("\nUse matching transmission line impedance less than %f Ohms\n",zmax);
printf("Change term in data statement to reflect a lower impedance.\n");
}

/****************************************************************************/

tuning()
{
/* Antenna adjustment calculations by N3GO 03/24/95 */

double f1, f2, dl;
static char f1s[21], f2s[21];
char tmp[82];

input("\nFrequency (MHz) where minimum VSWR is desired: ", &f2);

while (1) {
input("\nMeasured minimum VSWR frequency (MHz): ", &f1);
if (! f1) return;

dl = (491.78 * (f2-f1)) / (f1*f2); /* Equation B1 */

if (! dl) break;

if (dl > 0)
printf("\nReduce the length of the halfwave element "
"by: %f cm\n", dl * 12 * 2.54);
else
printf("\nIncrease the length of the halfwave element "
"by: %f cm\n", fabs(dl) * 12 * 2.54);
}
printf("\nGood Job!!!\n");
}

/****************************************************************************/

velocity()
{
double f1, f2, v, l, l1, l2, dl;
static char f1s[21], f2s[21], vs[21], ls[21];
char c, tmp[82], yesno;

input("\nDesired operating frequency (MHz): ", &f1);
input("\nEstimate the velocity factor of the transmission line: ",
&v);
printf("\nCut an electrical half wavelength sample.\n");

l1 = (v * 491.78) / f1; /* Equation C1 */

printf("\nCut sample length to: %f cm\n",l1 * 12 * 2.54);

while (1) {
input("\nFrequency (MHz) where VSWR is lowest: ", &f2);

/* Compute new velocity factor estimate based on VSWR measurement result */

v = l1 * f2 / 491.78;

printf("\nCurrent velocity factor estimate: %f\n",v);

/* Compute new sample length based on new velocity factor estimate */

l2 = 491.78 * v / f1;

/* Compute length change required for desired frequency sample */

dl = l2 - l1;

printf("\nAdjusted length of %f MHz sample: %f\n",
f1, l2 * 12 * 2.54);
printf("\nDoes the VSWR at %.4f MHz equal that of the "
"dummy load? ", f2);
while(! scanf(" %c", &yesno))
getchar();
if (yesno == 'y')
break;

if (dl <= 0)
printf("\nReduce the stub length by "
"%f cm\n", fabs(dl) * 12 * 2.54);
else
printf("\nIncrease the stub length by "
"%f cm\n", dl * 12 * 2.54);

l1 = l2;
}

input("\nMeasured physical length (cm): ", &l);
l = l / 2.54 / 12;

/* Equation C3 in Appendix C */

printf("\nThe velocity factor is: %f\n", l * f2 / 491.78);
}

/***************************************************************************/

main()
{
char c;

printf("\nJ-Pole design calculations by N3GO Gary O'Neil\n");
printf("----------------------------------------------\n");

while (1) {
printf("\n1 Antenna design calculations\n");
printf("2 Antenna adjustment calculations\n");
printf("3 Velocity factor calculations\n");
printf("Q Quit\n");
while (! scanf(" %c", &c))
getchar();
switch(c) {
case '1':
design();
break;
case '2':
tuning();
break;
case '3':
velocity();
break;
case 'q':
case 'Q':
exit(0);
}
}
}