Attenuation Calculator

What Is Signal Attenuation?

Attenuation measures how much a signal is reduced as it passes through a cable, amplifier stage, or acoustic path. Engineers express it in decibels (dB), a logarithmic unit that makes large ratios easier to compare.

Attenuation Formulas

For power ratios:

$$A_{\text{dB}} = 10 \log_{10}\left(\frac{P_{\text{in}}}{P_{\text{out}}}\right)$$

For voltage (or current) ratios:

$$A_{\text{dB}} = 20 \log_{10}\left(\frac{V_{\text{in}}}{V_{\text{out}}}\right)$$

Example: 100 W input and 10 W output gives $10 \log_{10}(10) = 10$ dB of power attenuation. Doubling voltage corresponds to 6 dB because $20 \log_{10}(2) \approx 6.02$.

When to Use Power vs Voltage

Use the power formula when comparing actual power levels (RF transmitters, optical links). Use the voltage formula for signal amplitudes in audio, RF voltage measurements, or when impedances are equal so power scales with voltage squared.

Frequently Asked Questions

Why is the voltage factor 20 instead of 10?

Power is proportional to voltage squared at constant impedance. Taking $10 \log_{10}(V^2) = 20 \log_{10}(V)$ accounts for that squaring.

Can attenuation be negative?

Yes. Negative dB means gain: output exceeds input. Positive dB means loss.

How do I add attenuation in dB?

Decibels add for cascaded stages. Two 3 dB pads in series give 6 dB total attenuation.

What if output equals input?

The ratio is 1 and $\log_{10}(1) = 0$, so attenuation is 0 dB (no loss).

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What Is Signal Attenuation?

Attenuation Formulas

When to Use Power vs Voltage

Frequently Asked Questions

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