#!/usr/pkg/bin/perl
use strict; 
use Math::BigFloat;
our @ARGV;

my $r = $ARGV[0];
my $L = $ARGV[1];
my $N = $ARGV[2];
my $C = $ARGV[3];

sub usage {
    print <<USAGE;
    $0 radius(cm) Lengh(cm) Turn Cap(pF)
USAGE
}

print $r,' ', $L,' ',$N,' ' , $C, "\n";

if ($#ARGV != 3 ) { usage();exit}

my $henry = 0.394 * $r * $r * $N * $N / ( 9 * $r  + 10 * $L);
								# microH  and  pico F
my $tune;
my $LC = $henry * $C;
$tune = 1000 / ( 2 * 3.14 * sqrt $LC );   # 1/ sqrt(10^-6 * 10^-12) = 10^9

printf("%15.2f micro henry, tune %15.2f MHz with %4.2f pF.\n", $henry, $tune, $C);
__END__
http://www.electronics-tutorials.com/receivers/crystal-radio-set.htm