#!/usr/bin/perl

sub log10 {
  log($_[0]) * (1 / log(10));
}

print "\n\n\t\tVHF/UHF Free Space Loss \\ Received Power Level Calculator\n\n";

while (!m/^([0-9.]+)(ft|FT|m|M|km|KM|mi|MI+)$/) {
	undef $_; undef $dis; undef $unit;
      	print "\nft = feet\n".
              "m  = meters\n".
              "km = kilometers\n".
              "mi = miles\n\n".
              "Enter Distance Between Antennas  [value][ft,m,km,mi]: ";
	chomp($_ = <STDIN>);
}

if (m/^([0-9.]+)(ft|FT|m|M|km|KM|mi|MI+)$/) {
	$dis = $1;
        $unit = $2;
}              

if ($unit =~ /ft/i) {
	$unit = "feet";
	$dist = $dis / 5280;
}

elsif ($unit eq "m" or $unit eq "M") {
	$unit = "meter";
	$dist = $dis * 0.00062137119;
}

elsif ($unit =~ /km/i) {
	$unit = "kilometer";
	$dist = $dis * 0.62137119;
}

elsif ($unit =~ /mi/i) {
	$unit = "mile";
	$dist = $dis;
}

print "\n";

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

print "\n";

while (!$pwr) {
	print "Enter Transmitter Power (in Watts): ";
	chomp($pwr = <STDIN>);
	$pwr =~ tr/0-9.//csd;
}

print "\n";

while (!$txant) {
	print "Enter Transmitter Antenna Gain (in dBi): ";
	chomp($txant = <STDIN>);
	$txant =~ tr/0-9.-//csd;
}

print "\n";

while (!$rxant) {
	print "Enter Receive Antenna Gain (in dBi): ";
	chomp($rxant = <STDIN>);
	$rxant =~ tr/0-9.-//csd;
}

$tx_dbm = 10 * log10($pwr) + 30;

$fs = (20 * (log10 $frq)) + (20 * (log10 ($dist * 1.609344))) + 32.447782;

$rx_dbm = $tx_dbm - $fs - ($txant + $rxant);

$rx_uvolt = (sqrt(( 10 ** ($rx_dbm / 10) / 1000) * 50)) * 1000000;

print "\n\n--------\n\n";
printf "          Antenna Spacing : %.3f %s%s\n", $dis, $unit, ($dis == 1) ? "" : "s";
printf "        Transmitter Power : %.3f Watts  (%.3f dBm)\n", $pwr, $tx_dbm;
printf "    Transmitter Frequency : %.3f MHz\n", $frq;
printf " Transmitter Antenna Gain : %.3f dB\n", $txant;
printf "     Receive Antenna Gain : %.3f dB\n\n", $rxant;
printf "         Received Voltage : %.9f microvolts\n", $rx_uvolt;
printf "           Received Power : %.3f dBm\n", $rx_dbm;
printf "   Free Space Attenuation : %.3f dB\n\n", $fs;