#!/usr/bin/env perl

# J-Pole Antenna Design

# Assumes 1/2 inch copper pipe for all sections
# and 50 ohm coax for feedline and balun.
# Element C length is not critical.
# Refer to ARRL Antenna Handbook for more information.
# and http://qrp.cc.nd.edu/qrp-l/hints/jpole/JPOLE.HTML

sub Cent {
2.54 * $inch;
}

sub Print {                        
print "\33[H\33[J".
      "                                  To Antenna  ^    ^        \n".
      "                                          ____|    |        \n".
      "       ____                              |    |    |        \n".
      "      |          *                       |    |    |        \n".
      "      |          *                      | |--| |--| |       \n".
      "      |          *                      | |  | |  | |       \n".
      "      |          *         ____         | |  | |  | | Balun \n".
      "      |          *   *         |        | |  | |__| | 50 ohm\n".
      "   A  |          *   *         |        | |  |______|       \n".
      "      |          *   *         | B      | |                 \n".
      "      |____      *   *     ____|        | |                 \n".
      "                 *****                  |   To Transmitter  \n".
      "                 *                          50 ohm          \n".
      "                 *   |                                      \n".
      "                  ___| C                                    \n\n";
}

print "\n\n\t\tJ-Pole Antenna Design\n\n";

while (!$frq) {
	print "Enter center frequency (in MHz): ";
	chomp($frq = <STDIN>);
	$frq =~ tr/0-9.//csd;
}

print "\n";

while (!$_) {
	print "Do you want to enter your own K factor? [y|n]: ";
	chomp($_ = <STDIN>);
	tr/ynYN//csd;
}

print "\n";

if (/y/i) {

	while (!$k) {
		print "Enter K factor (0.??): ";
		chomp($k = <STDIN>);
		$k =~ tr/0-9.//csd;
	}
}

elsif (/n/i) {

	$a = (((491.8 / $frq) * 2) * 12) / 0.5;

if ($a < 20) {
	$k = 0.92;
}

elsif ($a >= 21 && $a <= 40) {
	$k = 0.93
}

elsif ($a >= 41 && $a <= 100) {
	$k = 0.95;
}

elsif ($a >= 101 && $a <= 400) {
	$k = 0.96;
}                     

elsif ($a >= 401 && $a <= 2000) {
        $k = 0.97;
}

elsif ($a >= 2001 && $a <= 40000) {
        $k = 0.98;
}

elsif ($a > 40001) {
        $k = 0.99;
 }
}            

print "\n";

while (!$vf) {
	print "Enter velocity factor for the coax (0.??): ";
	chomp($vf = <STDIN>);
	$vf =~ tr/0-9.//csd;
}

$shrt_in = 2878 / $frq;
$lng_in = $k * ((5904 / $frq) + $shrt_in);
$balun = ($vf * 5904) / $frq;
$space = (22 / $frq) * 12;
$feed = (23 / $frq) * 12;

&Print;

print  "   K factor : $k\n";
printf "  Element A : %.2f inches (%.2f cm)\n", $lng_in, &Cent($inch = $lng_in);
printf "  Element B : %.2f inches (%.2f cm)\n", $shrt_in, &Cent($inch = $shrt_in);
printf "  Element C : %.2f inches (%.2f cm)\n", $space, &Cent($inch = $space);
printf "      Balun : %.2f inches (%.2f cm)\n", $balun, &Cent($inch = $balun);
printf " Feed point : %.2f inches (%.2f cm)\n\n", $feed, &Cent($inch = $feed);