Vswr Calculator

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VSWR Calculator body { font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif; background-color: #f8f9fa; color: #333; line-height: 1.6; margin: 0; padding: 20px; } .vswr-calc-container { max-width: 800px; margin: 30px auto; background-color: #fff; padding: 30px; border-radius: 8px; box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1); display: flex; flex-wrap: wrap; gap: 30px; } .calculator-section { flex: 1; min-width: 280px; } h1, h2 { color: #004a99; text-align: center; margin-bottom: 20px; } .input-group { margin-bottom: 20px; padding: 15px; border: 1px solid #e0e0e0; border-radius: 5px; background-color: #fdfdfd; } .input-group label { display: block; margin-bottom: 8px; font-weight: 600; color: #004a99; } .input-group input[type="number"] { width: calc(100% – 20px); padding: 10px; border: 1px solid #ccc; border-radius: 4px; font-size: 1rem; margin-top: 5px; box-sizing: border-box; } .input-group input[type="number"]:focus { border-color: #004a99; outline: none; box-shadow: 0 0 0 2px rgba(0, 74, 153, 0.2); } button { background-color: #004a99; color: white; padding: 12px 25px; border: none; border-radius: 5px; font-size: 1.1rem; cursor: pointer; transition: background-color 0.3s ease, transform 0.2s ease; width: 100%; margin-top: 10px; } button:hover { background-color: #003366; transform: translateY(-2px); } button:active { transform: translateY(0); } #result { margin-top: 30px; padding: 20px; background-color: #e8f5e9; /* Light green for success */ border: 1px solid #28a745; border-radius: 5px; text-align: center; font-size: 1.8rem; font-weight: bold; color: #28a745; word-wrap: break-word; } #result span { font-size: 1rem; font-weight: normal; color: #333; display: block; margin-top: 5px; } .article-section { margin-top: 40px; padding: 30px; background-color: #fff; border-radius: 8px; box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1); } .article-section h2 { text-align: left; margin-bottom: 15px; } .article-section p, .article-section ul, .article-section li { margin-bottom: 15px; color: #555; } .article-section code { background-color: #eef; padding: 2px 5px; border-radius: 3px; font-family: Consolas, Monaco, 'Andale Mono', 'Ubuntu Mono', monospace; } @media (max-width: 600px) { .vswr-calc-container { flex-direction: column; padding: 20px; } button { font-size: 1rem; padding: 10px 20px; } #result { font-size: 1.5rem; } }

VSWR Calculator

Calculate Standing Wave Ratio (VSWR) based on reflected and forward power, or voltage measurements.

Understanding VSWR (Voltage Standing Wave Ratio)

Voltage Standing Wave Ratio (VSWR), often pronounced "Vis-war," is a measure of the impedance mismatch in radio frequency (RF) systems. It quantifies how efficiently power is transferred from a source (like a transmitter) to a load (like an antenna) through a transmission line. An ideal match results in a VSWR of 1:1, meaning all power is delivered to the load. Any deviation from this ideal indicates reflected power returning towards the source, which can cause inefficiencies, overheating, and potential damage to the transmitter.

How VSWR is Calculated

VSWR can be calculated using either power measurements or voltage measurements. The formulas are derived from the relationship between forward and reflected waves in a transmission line.

1. Using Power Measurements:

When you can measure the forward power (Pfwd) and the reflected power (Pref) from the source, VSWR is calculated as:

VSWR = (1 + sqrt(Pref / Pfwd)) / (1 - sqrt(Pref / Pfwd))

This formula is based on the fact that power is proportional to the square of the voltage amplitude.

2. Using Voltage Measurements:

If you can measure the maximum voltage amplitude (Vmax) and the minimum voltage amplitude (Vmin) along the transmission line, VSWR is calculated as:

VSWR = Vmax / Vmin

Alternatively, if you can directly measure the forward voltage amplitude (Vfwd) and the reflected voltage amplitude (Vref) at a reference point (like the source end), you can use:

VSWR = (Vfwd + Vref) / (Vfwd - Vref)

This calculation assumes a perfect transmission line with negligible loss. The second voltage formula corresponds directly to the maximum and minimum voltage amplitudes along the line.

Interpreting VSWR Values:

  • 1:1: Perfect match. All power is delivered to the load.
  • 1.1:1 to 1.5:1: Excellent match. Very little reflected power.
  • 1.5:1 to 2.0:1: Good match. Generally acceptable for most applications.
  • 2.0:1 to 3.0:1: Fair match. Some power is reflected. Performance may be affected.
  • Above 3.0:1: Poor match. Significant reflected power. Potential for damage and reduced system efficiency.

Why VSWR Matters:

  • Efficiency: High VSWR means less power reaches the antenna, reducing transmission range and effectiveness.
  • Equipment Protection: Reflected power can cause excessive heat and damage to transmitters (especially solid-state amplifiers).
  • System Performance: In sensitive RF systems, poor VSWR can lead to signal distortion and interference.

Regularly checking VSWR is crucial for maintaining the health and performance of any RF system, from amateur radio setups to professional broadcast and telecommunications infrastructure.

function calculateVSWR() { var forwardPower = parseFloat(document.getElementById("forwardPower").value); var reflectedPower = parseFloat(document.getElementById("reflectedPower").value); var forwardVoltage = parseFloat(document.getElementById("forwardVoltage").value); var reflectedVoltage = parseFloat(document.getElementById("reflectedVoltage").value); var resultElement = document.getElementById("result"); resultElement.innerHTML = ""; // Clear previous result var vswr = null; var calculationType = ""; // Prioritize power calculation if available and valid if (!isNaN(forwardPower) && !isNaN(reflectedPower) && forwardPower > 0 && reflectedPower >= 0) { if (reflectedPower >= forwardPower) { resultElement.innerHTML = "Error: Reflected power cannot be greater than or equal to forward power."; return; } if (reflectedPower === 0) { // Handle perfect match case vswr = 1.0; calculationType = "based on power measurements (perfect match)"; } else { var ratio = reflectedPower / forwardPower; if (ratio >= 1) { resultElement.innerHTML = "Error: Reflected power ratio must be less than 1."; return; } vswr = (1 + Math.sqrt(ratio)) / (1 – Math.sqrt(ratio)); calculationType = "based on power measurements"; } } // If power calculation wasn't possible or yielded an error, try voltage calculation else if (!isNaN(forwardVoltage) && !isNaN(reflectedVoltage) && forwardVoltage > 0 && reflectedVoltage >= 0) { if (reflectedVoltage >= forwardVoltage) { resultElement.innerHTML = "Error: Reflected voltage cannot be greater than or equal to forward voltage."; return; } if (forwardVoltage – reflectedVoltage === 0) { resultElement.innerHTML = "Error: Division by zero. Forward voltage cannot equal reflected voltage."; return; } vswr = (forwardVoltage + reflectedVoltage) / (forwardVoltage – reflectedVoltage); calculationType = "based on voltage measurements"; } // If neither calculation is possible else if (isNaN(forwardPower) && isNaN(reflectedPower) && isNaN(forwardVoltage) && isNaN(reflectedVoltage)) { resultElement.innerHTML = "Please enter at least one set of values (Power or Voltage)."; return; } else if (isNaN(forwardPower) || isNaN(reflectedPower)) { // Partial power inputs, but not enough. Check voltages. if (!isNaN(forwardVoltage) && !isNaN(reflectedVoltage) && forwardVoltage > 0 && reflectedVoltage >= 0) { if (reflectedVoltage >= forwardVoltage) { resultElement.innerHTML = "Error: Reflected voltage cannot be greater than or equal to forward voltage."; return; } if (forwardVoltage – reflectedVoltage === 0) { resultElement.innerHTML = "Error: Division by zero. Forward voltage cannot equal reflected voltage."; return; } vswr = (forwardVoltage + reflectedVoltage) / (forwardVoltage – reflectedVoltage); calculationType = "based on voltage measurements"; } else { resultElement.innerHTML = "Please enter valid Forward and Reflected Power values, or Forward and Reflected Voltage values."; return; } } else if (isNaN(forwardVoltage) || isNaN(reflectedVoltage)) { // Partial voltage inputs, but not enough. Check powers. if (!isNaN(forwardPower) && !isNaN(reflectedPower) && forwardPower > 0 && reflectedPower >= 0) { if (reflectedPower >= forwardPower) { resultElement.innerHTML = "Error: Reflected power cannot be greater than or equal to forward power."; return; } if (reflectedPower === 0) { vswr = 1.0; calculationType = "based on power measurements (perfect match)"; } else { var ratio = reflectedPower / forwardPower; if (ratio >= 1) { resultElement.innerHTML = "Error: Reflected power ratio must be less than 1."; return; } vswr = (1 + Math.sqrt(ratio)) / (1 – Math.sqrt(ratio)); calculationType = "based on power measurements"; } } else { resultElement.innerHTML = "Please enter valid Forward and Reflected Power values, or Forward and Reflected Voltage values."; return; } } // Display result if a valid VSWR was calculated if (vswr !== null) { resultElement.innerHTML = vswr.toFixed(2) + "" + calculationType + ""; } else { // This else block handles cases where inputs are present but not fully valid for either calculation resultElement.innerHTML = "Please enter complete and valid input values for either power or voltage."; } }

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