#!/usr/bin/perl
#
#Utility to assist in measurement of effective noise bandwidth (ENB)
#of SSB receiver.
#Reads saved spectrum log from Spectrogram V11 of receiver response to
#white noise input, and calculates ENB.
#
# Copyright: Owen Duffy 06-04-2005. All rights reserved.

$id='$Id: sl2enb.pl,v 1.6 2007/09/03 23:03:06 owen Exp $';

use Getopt::Std;

printf("\nsl2enb $id\n",$enb1,$f1);


getopts('hc:l:');

if($opt_h){
  print "\nUsage: sl2enb.pl [-c ReferenceFrequency][-l LoCutFreq] <SpectrogramLogFile>\n\n";
  exit;
  }

$f2=1000;
$f3=$opt_c;
$locut=$opt_l;

#get spectrum resolution
while(<>){
  chomp; #strip newline
  if(!/^([\d\.]*) Hz Frequency Resolution$/){next;} #skip to resolution line
  s/^([\d\.]*) Hz Frequency Resolution$/$1/;
  $res=$_;
  last;
  }

#skip to col hdr
while(<>){
  chomp; #strip newline
  if(!/^Num/){next;}
  last;
  }

$pwrtot=0;
while(<>){
  next if (/^$/); #skip empty lines
  if (/^--/){last;}
  chomp; #strip newline
  ($num,$hz,$db)=split;
  next if $hz<$locut; #lo cut filter
  $pwr=10**($db/10);
  $obs[$#obs+1]="$pwr\t$hz";
  $pwrtot+=$pwr;
  if($hz>($f2-20) && $hz<($f2+20)){
    $midtot+=$pwr;
    $midn++;
    }
  }
#throw away the last obs, it is sometimes defective
$#obs--;

#1KHz (f2)
$f2pwr=$midtot/$midn;
$enb2=$pwrtot/$f2pwr*$res;

#find passband centre (f1)
@obs_s=sort {$b <=> $a} @obs;
$fl=100000;
($pwrmax,undef)=split('\t',$obs_s[0]);
#find fl and fu such that they are -10dB
for $x (@obs_s) {
  ($pwr,$hz)=split('\t',$x);
  if($pwr<$pwrmax/10){last;}
  if($fl>$hz){$fl=$hz};
  if($fu<$hz){$fu=$hz};
  }
#f1 is midway between fl and fu
$f1=($fl+$fu)/2;

#rescan the data to get the gain at f1.
$midtot=0;
$midn=0;
for $x (@obs_s) {
  ($pwr,$hz)=split('\t',$x);
  if($hz>($f1-20) && $hz<($f1+20)){
    $midtot+=$pwr;
    $midn++;
    }
  }
#passband centre (f1)
$f1pwr=$midtot/$midn;
$enb1=$pwrtot/$f1pwr*$res;

#rescan the data to get the gain at f3.
$midtot=0;
$midn=0;
if($f3>0){for $x (@obs_s) {
  ($pwr,$hz)=split('\t',$x);
  if($hz>($f3-20) && $hz<($f3+20)){
    $midtot+=$pwr;
    $midn++;
    }
  }
#specified freq (f3)
$f3pwr=$midtot/$midn;
$enb3=$pwrtot/$f3pwr*$res;
}

#show ENB wrt centre freq
printf("\nENB=%5.0fHz with respect to gain at %5.0fHz (passband centre frequency).\n\n",$enb1,$f1);
#if gain at f1 (1KHz) is greater than at centre freq -10dB, show ENB wrt f1
if($f2pwr>$f1pwr/10){
  printf("ENB=%5.0fHz with respect to gain at %5.0fHz.\n\n",$enb2,$f2);
  }
#if gain at f3 (command line arg) is greater than at centre freq -10dB, show ENB wrt f3
if($f3pwr>$f1pwr/10){
  printf("ENB=%5.0fHz with respect to gain at %5.0fHz (specified).\n\n",$enb3,$f3);
  }