SNR Measurement Estimator Calculator

• SNR (linear): SNR = Ps / Pn
• SNR (dB): SNR(dB) = 10 · log10(Ps / Pn)
• Voltage to power: P = Vrms² / R (same impedance for signal and noise)
• Thermal noise estimate: Pn = k · T · B · F, where F = 10^(NF/10)
• Averaging estimator: coherent gain ~ N, incoherent gain ~ sqrt(N)

1. Select an estimator mode that matches your measurement setup.
2. Enter signal and noise values using consistent units and bandwidth.
3. When using voltage, provide the correct impedance used in the test.
4. For thermal estimates, enter bandwidth, temperature, and noise figure.
5. Click Calculate to view results above the form.
6. Use CSV or PDF export to document the calculated values.

Signal-to-noise ratio (SNR) describes how clearly a measured signal rises above random noise. In real setups, SNR depends on bandwidth, detector settings, impedance, and how you estimate noise. Use the mode that matches your instrument readout, and record bandwidth with every exported result.

1) Define signal and noise consistently

For power readings, SNR compares average signal power to average noise power in the same bandwidth. For voltage readings, convert to power with P = Vrms² / R so the ratio reflects power, not raw amplitude.

2) Use linear and dB forms correctly

Linear SNR is Ps / Pn, while dB SNR is 10 · log10(Ps / Pn). A 10 dB change equals a 10× power-ratio change, and 3 dB is about 2×. In dB form, power readings subtract cleanly.

3) Bandwidth sets the measured noise

Noise power grows with bandwidth: a 10× wider bandwidth drops SNR by 10 dB for a fixed signal. Room-temperature thermal noise density is about -174 dBm/Hz before noise figure.

4) Thermal noise option and noise figure

The thermal estimate uses Pn = k·T·B·F, where F is set by the noise figure. It works best when noise is broadband and near thermal-limited behavior. For a quick reference, 290 K over 1 MHz is roughly -114 dBm before noise figure. If you see interference, spurs, or excess device noise, add extra noise power.

5) Averaging improvements: coherent vs incoherent

Averaging can improve SNR only if noise is uncorrelated across repeats. With coherent averaging (phase-aligned waveforms), improvement can scale near N. With magnitude or power averaging without phase alignment, improvement is typically closer to sqrt(N), provided the signal remains stable and the noise is random.

6) Impedance keeps voltage and power consistent

Voltage-based SNR becomes ambiguous when impedance changes. Use the actual load or input impedance so Vrms, watts, and dBm stay consistent.

7) Worked example with common numbers

If a tone reads -20 dBm and the measured noise in the same RBW reads -50 dBm, then SNR is 30 dB, meaning the signal power is 1000× larger than noise. If you widen RBW from 10 kHz to 100 kHz, noise rises by 10 dB and SNR drops by 10 dB.

8) Quality checks before exporting results

Verify noise was measured away from the signal bin and record RBW, averaging, and detector settings. Export CSV or PDF so assumptions stay attached to your computed SNR.

1) What is the difference between SNR and signal minus noise in dB?

SNR is a ratio of powers, so in dB it becomes subtraction: SNR(dB) = Signal(dBm) − Noise(dBm), but only when both are measured over the same bandwidth.

2) Can I use peak-to-peak voltage readings?

Yes. Convert to RMS first. For a sine wave, Vrms = Vpp/(2\u221A2). If the waveform is not sinusoidal, use a true-RMS measurement or compute RMS from samples.

3) Why does my SNR change when I change RBW or bandwidth?

Integrated noise power scales with bandwidth. Increasing bandwidth by 10× increases noise power by 10×, reducing SNR by 10 dB if the signal power stays constant.

4) When should I trust the thermal noise option?

Use it when noise is mainly thermal and broadband, such as resistive sources and many receivers. If your system shows strong interference, spurs, or device excess noise, include extra noise power.

5) Does averaging always improve SNR?

Only if noise is uncorrelated between averages and the signal stays stable. Coherent averaging can improve faster, but drift, phase noise, and nonstationary noise reduce the expected gain.

6) Why does the calculator show both dBm and watts?

Many instruments display dBm, while physics formulas often use watts. Showing both helps verify unit conversions and makes it easier to compare results with datasheets and lab notes.

7) What should I export to document a measurement?

Export SNR, signal and noise levels, impedance, bandwidth, temperature, noise figure, and any added noise assumptions. That set allows someone else to reproduce the estimate and compare setups fairly.