Insertion Loss Calculator

What Is Insertion Loss?

Insertion loss measures how much a component or network reduces signal level when placed in a circuit. RF filters, attenuators, and couplers are rated in decibels (dB). This calculator converts before-and-after power or voltage readings into insertion loss.

Formulas

Power ratio mode:

$$IL = 10 \log_{10}\left(\frac{P_{\text{before}}}{P_{\text{after}}}\right)$$

Voltage ratio mode:

$$IL = 20 \log_{10}\left(\frac{V_{\text{before}}}{V_{\text{after}}}\right)$$

Power uses a factor of 10 because power is proportional to amplitude squared. Voltage mode uses 20 log for the same reason.

Practical Notes

Positive insertion loss means the signal is weaker after insertion. A 3 dB loss means half the power is delivered. A 10 dB loss means only one-tenth of the power remains.

Frequently Asked Questions

When should I use power vs voltage mode?

Use power mode when you measure power directly. Use voltage mode when you only have voltage readings on the same impedance.

Why is the voltage formula multiplied by 20?

Power is proportional to voltage squared. Taking 10 log of a power ratio equals 20 log of the corresponding voltage ratio.

Can insertion loss be negative?

Yes, if the after value exceeds the before value, the network amplifies rather than attenuates. That is gain, shown as negative loss in dB.

What does 10 dB loss mean?

10 dB corresponds to a 10:1 power ratio. Only 10% of the input power reaches the output.

Do I need matched impedances?

For accurate power-based measurements, source and load impedances should match the test setup. Voltage mode assumes the same impedance before and after.

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What Is Insertion Loss?

Formulas

Practical Notes

Frequently Asked Questions

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