function showcredit()
{
var credit
credit="Script programmed by Jens T.Saetre 05112000"
credit+="\n08122002 Changed layout"
credit+="\n26052003 Changed G/T calculation"
credit+="\n26052003 LNB VSWR probably not contribute in G/T , use 1:1"
credit+="\n26082003 Changed G/T calculation- shold give correct value now"
credit+="\nUpdated 26082003"
window.alert(credit);

//var theResponse = window.prompt("Welcome?","Enter your name here.");
}



function Loss_dB()
{
return(-10*log10(1-(Loss_Percent()/100)));
}


function Loss_Percent()
{
var vswr,loss
vswr=1*document.Antenna.VSWR.value;
loss=100* Math.pow(  (  (vswr-1)/(vswr+1)  ),2   );
return(loss);
}



function main()
{
var GTsys,GainFeed_dB,SystemNoiseFiguredB,AntennaNoiseFigureKelvin,AntennaNoiseFiguredB

SystemNoiseFiguredB= 10*log10(1+(Tsys()/290)) ;

AntennaNoiseFigureKelvin=1*document.Antenna.NoiseTemperature.value;
AntennaNoiseFiguredB=10*log10(1+(AntennaNoiseFigureKelvin/290)) ;
document.Antenna.dBAntennaNoiseFigure.value=formatvalue(AntennaNoiseFiguredB, 5);

document.Antenna.SystemNoiseFigure.value=formatvalue(SystemNoiseFiguredB,5);

GainFeed_dB=1*document.Antenna.FeedLoss.value;
document.Antenna.Gain.value=formatvalue(AntennaGain(), 5);
document.Antenna.SystemNoiseTemperature.value=formatvalue(Tsys(), 5);
GTsys= AntennaGain() - 10*log10(Tsys()); // 


// ***OLD formula - probably wrong when G/T is referred to the antenna feed
//GTsys= AntennaGain() -Loss_dB() -GainFeed_dB - 10*log10(Tsys()); // 
document.Antenna.Log10SystemNoiseFigure.value=formatvalue(10*log10(Tsys()),5);

document.Antenna.GTsys.value=formatvalue(GTsys, 5);
//var theResponse = window.prompt("Welcome?",Loss_dB());





}


function log10(X)
{
return( Math.log(X)/Math.log(10)  );
// works OK !
}


function AntennaGain()
{
var AntennaEfficiency,RxFrequency,Gain,AntennaDiameter
RxFrequency=1*document.Antenna.Frequency.value;
AntennaEfficiency=document.Antenna.Efficiency.value;
AntennaDiameter=document.Antenna.Diameter.value ;
Gain=10*log10(AntennaEfficiency/100) +20*log10(RxFrequency/1000) +20*log10(AntennaDiameter)+20.4 ;
//window.prompt(Gain,"Test verdi");
return(Gain);
}


function Tsys()
{
var LNBNoiseFigure,LNBNoiseTemperature,GainFeed,FeedLoss_dB,FeedLoss,AntennaNoiseTemperature,T_sys
GainFeed_dB=1*document.Antenna.FeedLoss.value;
LNBNoiseFigure=1*document.Antenna.LNBNoiseFigure.value;
LNBNoiseTemperature= 290*(  Math.pow( 10,(LNBNoiseFigure/10)  )  -1) ;
AntennaNoiseTemperature=1*document.Antenna.NoiseTemperature.value;
GainFeed=Math.pow(10,(-FeedLoss_dB/10));
//T_sys= AntennaNoiseTemperature + (LNBNoiseTemperature/GainFeed)  ;   ikke riktig !!!!

T_sys=AntennaNoiseTemperature + 290*(  Math.pow( 10,((GainFeed_dB+Loss_dB())/10)  )  -1) + 290*(  Math.pow( 10,((LNBNoiseFigure)/10)  )  -1)  *(Math.pow( 10,((GainFeed_dB+Loss_dB())/10)));


//window.prompt(FeedLoss,"Test verdi");

return(T_sys)
}




function toNoiseTemperature()
{
var NoiseFigure,NoiseTemperature
NoiseFigure=1*document.Antenna.LNBNoiseFigure.value;
//NF=10log(1+Teq/290)

NoiseTemperature= 290*(  Math.pow( 10,(NoiseFigure/10)  )  -1) ;
document.Antenna.LNBNoiseTemperature.value=formatvalue(NoiseTemperature, 5);
}


function toNoiseFigure()
{
var NoiseFigure,NoiseTemperature
NoiseTemperature=1*document.Antenna.LNBNoiseTemperature.value;
NoiseFigure= 10*log10(1+NoiseTemperature/290) ;
document.Antenna.LNBNoiseFigure.value=formatvalue(NoiseFigure, 5);
}







function formatvalue(input, rsize) // Desimal avrunding
  {
   var invalid = "**************************";
   var nines = "999999999999999999999999";
   var strin = "" + input;
   var fltin = parseFloat(strin);
   if (strin.length <= rsize) return strin;
   if (strin.indexOf("e") != -1 ||
       fltin > parseFloat(nines.substring(0,rsize)+".4"))
      return invalid.substring(0, rsize);
   var rounded = "" + (fltin + (fltin - parseFloat(strin.substring(0, rsize))));
   return rounded.substring(0, rsize);
}