Vsr Calculator

VSWR Calculator

This calculator helps you determine the Voltage Standing Wave Ratio (VSWR), Reflection Coefficient, Return Loss, and Mismatch Loss based on the forward and reflected power of your radio frequency (RF) system. A lower VSWR indicates a more efficient system with less power being reflected back to the transmitter.

function calculateVSWR() { var forwardPower = document.getElementById("forwardPower").value; var reflectedPower = document.getElementById("reflectedPower").value; var resultDiv = document.getElementById("result"); var pf = parseFloat(forwardPower); var pr = parseFloat(reflectedPower); if (isNaN(pf) || isNaN(pr) || pf <= 0) { resultDiv.innerHTML = 'Please enter valid, positive numbers for power. Forward Power must be greater than zero.'; return; } if (pr pf) { resultDiv.innerHTML = 'Reflected Power cannot be greater than Forward Power.'; return; } var reflectionCoefficient, vswr, returnLoss, mismatchLoss, reflectedPowerPercent; if (pr == 0) { reflectionCoefficient = 0; vswr = 1; returnLoss = Infinity; } else { reflectionCoefficient = Math.sqrt(pr / pf); vswr = (1 + reflectionCoefficient) / (1 – reflectionCoefficient); returnLoss = -20 * Math.log10(reflectionCoefficient); } mismatchLoss = 10 * Math.log10(1 – Math.pow(reflectionCoefficient, 2)); reflectedPowerPercent = (pr / pf) * 100; var outputHTML = '

Calculation Results:

'; outputHTML += 'VSWR: ' + vswr.toFixed(2) + ':1'; outputHTML += 'Reflection Coefficient (Γ): ' + reflectionCoefficient.toFixed(3) + "; if (returnLoss === Infinity) { outputHTML += 'Return Loss: ∞ dB (Perfect Match)'; } else { outputHTML += 'Return Loss: ' + returnLoss.toFixed(2) + ' dB'; } outputHTML += 'Mismatch Loss: ' + Math.abs(mismatchLoss).toFixed(2) + ' dB'; outputHTML += 'Reflected Power: ' + reflectedPowerPercent.toFixed(2) + '%'; resultDiv.innerHTML = outputHTML; }

What is VSWR?

Voltage Standing Wave Ratio (VSWR) is a measure of how efficiently radio-frequency (RF) power is transmitted from a source, through a transmission line (like a coaxial cable), and into a load (like an antenna). It quantifies the mismatch between the impedance of the transmission line and the load. In an ideal system, all power is transmitted to the load. In reality, some power is reflected back towards the source due to impedance mismatches.

Understanding Your VSWR Results

The VSWR is expressed as a ratio, with 1:1 being a perfect match. Here's a general guide to interpreting the results:

• 1.0:1 to 1.5:1 – Excellent. An ideal or near-perfect match, with minimal power loss.
• 1.5:1 to 2.0:1 – Good. A safe and acceptable match for most applications.
• 2.0:1 to 3.0:1 – Fair to Poor. Some power is being reflected. It may be acceptable for receiving, but for transmitting, it could cause issues and should be investigated.
• Above 3.0:1 – Bad. Significant power is being reflected. This can reduce system performance and potentially damage the transmitter's output stage due to the reflected energy. Immediate attention is required.

How is VSWR Calculated?

The calculator uses the forward power (power from the transmitter) and reflected power (power returned from the load) to determine the key metrics. The core steps are:

1. Calculate the Reflection Coefficient (Γ): This is the ratio of the reflected voltage to the forward voltage. It's calculated as the square root of the reflected power divided by the forward power: Γ = sqrt(Pr / Pf).
2. Calculate VSWR: Once the reflection coefficient is known, VSWR is found using the formula: VSWR = (1 + Γ) / (1 - Γ).
3. Calculate Return Loss: This is the reflection coefficient expressed in decibels (dB). It measures the power of the reflected signal relative to the incident signal. A higher return loss is better. Formula: Return Loss = -20 * log10(Γ).

Practical Example

Let's say you are using a transmitter that outputs 100 Watts of forward power. You use an inline meter and measure 4 Watts of reflected power coming back from the antenna.

• Forward Power (Pf): 100 W
• Reflected Power (Pr): 4 W

Using the formulas:

1. The reflection coefficient (Γ) is sqrt(4 / 100) = sqrt(0.04) = 0.2.
2. The VSWR is (1 + 0.2) / (1 - 0.2) = 1.2 / 0.8 = 1.5.

The resulting VSWR is 1.5:1, which is considered an excellent match for an antenna system.