Coaxial cable, often called "coax," is a type of electrical cable with an inner conductor surrounded by an insulating layer,
which is then surrounded by a braided metal shield, and finally an outer insulating layer. This construction makes it
ideal for carrying high-frequency electrical signals, such as those used for radio, television, and data transmission,
because the shield protects the signal from external interference and prevents the signal from radiating outwards.
However, coaxial cables are not perfect conductors. As signals travel through the cable, they experience a reduction in power,
known as signal loss or attenuation. This loss is a critical factor in designing communication systems, as excessive loss can
degrade signal quality, reduce transmission range, or even render the communication impossible.
Factors Affecting Coaxial Cable Loss
Several factors contribute to signal loss in coaxial cables:
Frequency: Higher frequencies experience greater attenuation than lower frequencies. This is because
the AC resistance (skin effect) of the conductors increases with frequency.
Cable Length: Naturally, the longer the cable, the more signal loss will occur. Loss is typically
specified per unit length (e.g., dB per 100 meters).
Cable Construction (Type/Dielectric): The materials used for the inner conductor, dielectric (insulator),
and shield, as well as their dimensions, significantly impact loss. Different types of coax (like RG-58, RG-6, RG-11)
are designed for different applications and have varying loss characteristics. The dielectric material (solid polyethylene,
foamed polyethylene, etc.) plays a crucial role in the cable's impedance and loss.
Connectors and Splices: Each connector, splice, or adapter introduces a small amount of loss due to impedance
mismatches and imperfect contact. While individual connector loss is usually small (e.g., 0.1-0.5 dB), the cumulative effect
of many connectors can become significant.
Temperature: While less significant than other factors for typical installations, temperature can slightly affect
the electrical properties of the cable materials.
Calculating Coaxial Cable Loss
The total signal loss in a coaxial cable system is generally calculated as the sum of the loss due to the cable itself and the
loss introduced by connectors.
Cable Loss Calculation:
The loss in the cable itself (in dB per unit length) is often provided by the manufacturer and typically varies with frequency.
A common approximation for attenuation ($A$) in dB per unit length (e.g., per 100 meters) at a given frequency ($f$) is:
$A \approx K_1 \sqrt{f} + K_2 f$
Where:
$f$ is the frequency in MHz.
$K_1$ is a constant related to conductor losses (skin effect).
$K_2$ is a constant related to dielectric losses.
These constants ($K_1$, $K_2$) are specific to the cable type and construction. For simplicity in this calculator, we use
pre-defined attenuation figures for common cable types at specific frequencies. The loss per meter is then derived, and
multiplied by the total cable length.
Connector Loss Calculation:
Each connector adds a fixed amount of loss, regardless of frequency or length. This is often estimated based on the quality
of the connector and installation. A typical value might be 0.2 dB per connector.
Total Loss:
The total loss ($L_{total}$) is the sum of the cable loss and the total connector loss:
$L_{total} = (\text{Attenuation per meter} \times \text{Cable Length}) + (\text{Loss per connector} \times \text{Number of Connectors})$
The result is typically expressed in decibels (dB).
Example Use Cases
Home Entertainment: Calculating loss for TV antenna feeds (CATV, Satellite) to ensure good picture quality.
Ham Radio: Determining signal strength at the antenna or receiver for HF/VHF/UHF communications.
Network Installation: Estimating loss in Ethernet over coax (MoCA) or CCTV camera systems.
Test & Measurement: Ensuring minimal signal degradation in sensitive RF test setups.
Interpreting the Results
A lower dB loss is always desirable. For sensitive applications (like satellite TV or weak signal radio), even a few dB of loss
can be critical. For less sensitive applications, higher loss might be acceptable. This calculator provides a baseline estimate;
real-world losses can vary slightly due to installation quality, cable aging, and environmental factors.
function getAttenuationData(cableType, frequency) {
// Attenuation data (dB per 100 meters) at specific frequencies (MHz)
// Sources vary; these are approximate values for illustration.
// Format: { cableType: { freq1: val1, freq2: val2, … } }
var attenuationData = {
"RG58": { 50: 10.0, 100: 15.0, 400: 32.0, 1000: 55.0 },
"RG59": { 50: 7.0, 100: 10.0, 400: 21.0, 1000: 35.0 },
"RG6": { 50: 5.0, 100: 7.0, 400: 15.0, 1000: 25.0, 2000: 38.0 },
"RG11": { 50: 3.5, 100: 5.0, 400: 10.0, 1000: 17.0, 2000: 26.0 },
"RG213":{ 50: 6.5, 100: 9.5, 400: 20.0, 1000: 33.0 }
};
var specificData = attenuationData[cableType];
if (!specificData) return null; // Cable type not found
// Find the closest frequency data point or interpolate if needed
// For simplicity here, we'll just try to find a direct match or the next lower one
var freqs = Object.keys(specificData).map(Number).sort(function(a, b){ return a – b; });
var effectiveFreq = frequency;
var attenuationPer100m = null;
// Simple lookup: Try to find the exact frequency
if (specificData.hasOwnProperty(frequency)) {
attenuationPer100m = specificData[frequency];
} else {
// If exact frequency not found, find the closest lower frequency data point
for (var i = freqs.length – 1; i >= 0; i–) {
if (freqs[i] <= frequency) {
attenuationPer100m = specificData[freqs[i]];
// Adjust for frequency difference if necessary (linear approximation)
if (i + 1 freqs[i]) {
var nextFreq = freqs[i+1];
var nextAtten = specificData[nextFreq];
// Crude linear interpolation/extrapolation for illustrative purposes
// A more accurate model would be logarithmic or polynomial
if (nextAtten !== undefined) {
var freqRatio = (frequency – freqs[i]) / (nextFreq – freqs[i]);
attenuationPer100m = attenuationPer100m + freqRatio * (nextAtten – attenuationPer100m);
}
}
break;
}
}
// If frequency is lower than the lowest available data point
if (attenuationPer100m === null && freqs.length > 0) {
attenuationPer100m = specificData[freqs[0]];
// Possibly extrapolate downwards – simple model might not handle this well
}
}
if (attenuationPer100m === null) {
console.warn("Attenuation data not available for the specified frequency for " + cableType);
return null;
}
// Convert attenuation from dB per 100m to dB per meter
var attenuationPerMeter = attenuationPer100m / 100.0;
return attenuationPerMeter;
}
function calculateLoss() {
var cableLength = parseFloat(document.getElementById("cableLength").value);
var frequency = parseFloat(document.getElementById("frequency").value);
var cableType = document.getElementById("cableType").value;
var connectors = parseInt(document.getElementById("connectors").value);
var resultDiv = document.getElementById("result");
resultDiv.style.display = 'block'; // Make sure the result div is visible
// Input validation
if (isNaN(cableLength) || cableLength <= 0) {
resultDiv.innerHTML = "Error: Please enter a valid positive cable length.";
resultDiv.style.color = "#dc3545"; // Red for error
return;
}
if (isNaN(frequency) || frequency <= 0) {
resultDiv.innerHTML = "Error: Please enter a valid positive frequency.";
resultDiv.style.color = "#dc3545"; // Red for error
return;
}
if (isNaN(connectors) || connectors < 0) {
resultDiv.innerHTML = "Error: Please enter a valid number of connectors (0 or more).";
resultDiv.style.color = "#dc3545"; // Red for error
return;
}
var attenuationPerMeter = getAttenuationData(cableType, frequency);
var connectorLossPerUnit = 0.2; // Approximate loss per connector in dB
if (attenuationPerMeter === null) {
resultDiv.innerHTML = "Error: Attenuation data not found for " + cableType + " at " + frequency + " MHz.";
resultDiv.style.color = "#dc3545"; // Red for error
return;
}
var cableLoss = cableLength * attenuationPerMeter;
var totalConnectorLoss = connectors * connectorLossPerUnit;
var totalLoss = cableLoss + totalConnectorLoss;
// Ensure total loss isn't negative due to potential rounding or data issues
if (totalLoss < 0) totalLoss = 0;
resultDiv.innerHTML = "Total Estimated Loss: " + totalLoss.toFixed(2) + " dB";
resultDiv.style.color = "#004a99"; // Professional blue for result
// You might want to add conditional styling based on the magnitude of loss
if (totalLoss > 10) {
resultDiv.style.borderColor = "#ffc107"; // Yellow for significant loss
resultDiv.style.color = "#856404";
}
if (totalLoss > 20) {
resultDiv.style.borderColor = "#dc3545"; // Red for very high loss
resultDiv.style.color = "#721c24";
}
}
function resetCalculator() {
document.getElementById("cableLength").value = "";
document.getElementById("frequency").value = "";
document.getElementById("cableType").selectedIndex = 0; // Reset to first option
document.getElementById("connectors").value = "0";
document.getElementById("result").innerHTML = "";
document.getElementById("result").style.display = 'none'; // Hide result
}