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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    */

#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
#include <math.h>

main()
{
	HideCur();
	while(1)
	{
		clrscr();
		printf("J-Pole design calculations by N3GO Gary O'Neil\n");
		printf("----------------------------------------------\n\n");

		printf("(1) Antenna design calculations\n");
		printf("(2) Antenna adjustment calculations\n");
		printf("(3) Velocity factor calculations\n\n");
		printf("(Q) Quit\n");
		switch(bioskey(0) & 0xff) {
			case '1': design();break;
			case '2': tuning();break;
			case '3': velocity();break;
			case 'q':
			case 'Q': ShowCur();
						 exit(0);
		}
	}
}


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;
char s[20];

	clrscr();

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

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

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

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

	input("                     Velocity factor: ",s,&v);

	while(1)
	{
		clrscr();

/*  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("   Frequency 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\n\n");
		printf("Impedances used for this calculation are as follows: \n");
		printf("\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);
		printf("\n\n\n");
		input("New Velocity factor (enter zero to quit): ",s,&v);
		if(v == 0) return;
	}

errexit:
	printf("Use 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;
char s[20];

	clrscr();
	printf("\n\n\n");
	input("       Frequency (MHz) where minimum VSWR is desired: ",s,&f2);
	printf("\n");

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

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

		if(! dl) break;

		if(dl > 0)
			printf("    Reduce the length of the halfwave element by: %f cm\n",dl * 12 * 2.54);
		else
			printf("  Increase the length of the halfwave element by: %f cm\n",fabs(dl) * 12 * 2.54);

		printf("\n\n");
	}
	clrscr();
	printf("\n\n\n          Good Job!!!\n");
	getch();
}


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


velocity()
{
double f1,f2,v,l,l1,l2,dl;
char s[20];
char c;

	clrscr();
	printf("\n\n\n");
	input("              Desired operating frequency (MHz): ",s,&f1);
	printf("\n");
	input("      Estimate the velocity factor of the transmission line: ",s,&v);
	printf("\n");
	printf("              Cut an electrical half wavelength sample.\n");

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

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

	while(1)
	{
		input("            Frequency (MHz) where VSWR is lowest: ",s,&f2);
		clrscr();
		printf("\n\n");

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

		v = l1 * f2 / 491.78;

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

/*  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("      Adjusted length of %f MHz sample: %f\n", f1, l2 * 12 * 2.54);
		printf("\n\n\n");
		printf("         Does the VSWR at %.4f MHz equal that of the dummy load?", f2);

		c = bioskey(0) & 0xff;
		if((c == 'y') || (c == 'Y')) break;

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

		l1 = l2;
	}

	clrscr();
	printf("\n\n");
	input("        Measured physical length (cm): ",s,&l);
	l = l / 2.54 / 12;

/*  Equation C3 in Appendix C */

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


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


input(char *p, char *s, double *v)
{
	printf("%s",p);
	ShowCur();
	gets(s);
	HideCur();
	*v = atof(s);
}

HideCur()
{
	asm{
		push ax
		push cx

		mov ah,01h
		mov ch,00100110b
		mov cl,00000111b
		int 10H

		pop cx
		pop ax
	}
}

ShowCur()
{
	asm{
		push ax
		push cx

		mov ah,01H
		mov ch,00000110b
		mov cl,00000111b
		int 10H

		pop cx
		pop ax
	}
}
.

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