function perRound(num, precision) {

var precision = 3; //default value if not passed from caller, change if desired

// remark if passed from caller

precision = parseInt(precision); // make certain the decimal precision is an integer

var result1 = num * Math.pow(10, precision);

var result2 = Math.round(result1);

var result3 = result2 / Math.pow(10, precision);

return zerosPad(result3, precision);

}

function zerosPad(rndVal, decPlaces) {

var valStrg = rndVal.toString(); // Convert the number to a string

var decLoc = valStrg.indexOf("."); // Locate the decimal point

// check for a decimal

if (decLoc == -1) {

decPartLen = 0; // If no decimal, then all decimal places will be padded with 0s

// If decPlaces is greater than zero, add a decimal point

valStrg += decPlaces > 0 ? "." : "";

}

else {

decPartLen = valStrg.length - decLoc - 1; // If there is a decimal already, only the needed decimal places will be padded with 0s

}

var totalPad = decPlaces - decPartLen; // Calculate the number of decimal places that need to be padded with 0s

if (totalPad > 0) {

// Pad the string with 0s

for (var cntrVal = 1; cntrVal <= totalPad; cntrVal++)

valStrg += "0";

}

return valStrg;

}

// send the value in as "num" in a variable

// clears field of default value

function clear_field(field) {

if (field.value==field.defaultValue) {

field.value=''

}

}

function dbw2watts(inValue)

{

return Math.round(Math.pow(10,eval(inValue)/10)*100000)/100000;

}

function watts2dbw(inValue)

{

return Math.round(10 * Math.log(eval(inValue))/Math.LN10 *

100000)/100000;

}

function txant(form)

{

EmptyString = ""

form.erpdbw.value = EmptyString;

form.eirpdbw.value = EmptyString;

form.eirpwatts.value = EmptyString;

form.erpwatts.value = EmptyString;

dipolegain = 10 * Math.log(1.64)/Math.LN10;

form.tpo.value = eval(form.tpo.value);

form.antgain.value = eval(form.antgain.value);

// 1/2 wave dipole gain = 1.64dB

if (form.tpounit.selectedIndex)

{

if (form.antgainunit.selectedIndex)

{

form.erpdbw.value = parseFloat(form.tpo.value) + parseFloat(form.antgain.value);

form.eirpdbw.value = parseFloat(form.erpdbw.value) + parseFloat(dipolegain);

form.erpdbwr.value = perRound(parseFloat(form.tpo.value) + parseFloat(form.antgain.value));

form.eirpdbwr.value = perRound(parseFloat(form.erpdbw.value) + parseFloat(dipolegain));

}

else

{

form.eirpdbw.value = parseFloat(form.tpo.value) + parseFloat(form.antgain.value);

form.erpdbw.value = parseFloat(form.eirpdbw.value) - parseFloat(dipolegain);

form.eirpdbwr.value = perRound(parseFloat(form.tpo.value) + parseFloat(form.antgain.value));

form.erpdbwr.value = perRound(parseFloat(form.eirpdbw.value) - parseFloat(dipolegain));

}

}

else

{

if (form.antgainunit.selectedIndex)

{

form.erpdbw.value = parseFloat(watts2dbw(form.tpo.value)) + parseFloat(form.antgain.value);

form.eirpdbw.value = parseFloat(form.erpdbw.value) + parseFloat(dipolegain);

form.erpdbwr.value = perRound(parseFloat(watts2dbw(form.tpo.value)) + parseFloat(form.antgain.value));

form.eirpdbwr.value = perRound(parseFloat(form.erpdbw.value) + parseFloat(dipolegain));

}

else

{

form.eirpdbw.value = parseFloat(watts2dbw(form.tpo.value)) + parseFloat(form.antgain.value);

form.erpdbw.value = parseFloat(form.eirpdbw.value) - parseFloat(dipolegain);

form.eirpdbwr.value = perRound(parseFloat(watts2dbw(form.tpo.value)) + parseFloat(form.antgain.value));

form.erpdbwr.value = perRound(parseFloat(form.eirpdbw.value) - parseFloat(dipolegain));

}

}

form.eirpwatts.value = dbw2watts(form.eirpdbw.value);

form.erpwatts.value = dbw2watts(form.erpdbw.value);

form.eirpwattsr.value = perRound(dbw2watts(form.eirpdbw.value));

form.erpwattsr.value = perRound(dbw2watts(form.erpdbw.value));

}

//-->

The Effective Isotropic Radiated Power (EIRP) is the apparent power transmitted towards the receiver, if it is assumed that the signal is radiated equally in all directions, such as as a spherical wave emanating from a point source; in other words, the arithmetic product of the power supplied to an antenna and its gain. Begin by testing the transmitter with a good dummy load and a good calibrated watt meter. Enter that value. Then enter the antenna gain. Finally, click on the Calculate button for the pure ERP and EIRP. This calculator is considering only power and antenna gain.

By definition, ERP is the abbreviation for Effective Radiated Power that is directed in a given direction. It is the power supplied to an antenna multiplied by the antenna gain in a given direction. If the direction is not specified, the direction of maximum gain is assumed and the type of reference antenna should be specified. It is also the product of the power supplied to the antenna and its gain relative to a half-wave dipole in a given direction and it is the effective radiated power of a transmitter (with antenna, transmission line, duplexers, etc.) Also, it is the power that would be necessary at the input terminals of a reference half-wave dipole antenna in order to produce the same maximum field intensity. ERP is usually calculated by multiplying the measured transmitter output power by the specified antenna system gain, relative to a half-wave dipole, in the direction of interest.

As a matter of definition, dB is the accepted abbreviation for decibel(s). One tenth of the common logarithm of the ratio of relative powers, equal to 0.1B (bel). Further, dBW is the abbreviation for dB referenced to one watt. The decibel is the conventional relative power ratio, rather than the bel, for expressing relative powers because the decibel is smaller and therefore more convenient than the bel. The dB is used rather than arithmetic ratios or percentages because when circuits are connected in series, expressions of power level, in dB, may be arithmetically added and subtracted. For example, in an RF transmission system, if a known amount of RF power, is fed into the system, and the losses, in dB, of each component (for example, lengths of feeder coax, connectors, duplexers, etc.) are known, the overall system loss may be quickly calculated with simple addition and subtraction.