Formula used
- Noise factor: F = SNR_in / SNR_out, and NF(dB) = 10·log10(F).
- From SNR in dB: NF(dB) = SNR_in(dB) − SNR_out(dB).
- Equivalent noise temperature: Te = (F − 1)·T0, where T0 is the reference temperature.
- Cascaded (Friis): F_total = F1 + (F2 − 1)/G1 + (F3 − 1)/(G1·G2) + …, with gains G in linear scale.
- Thermal noise power: N = k·Tsys·B, where Tsys = F_total·T0 and B is bandwidth.
How to use this calculator
- Select a calculation mode that matches your available measurements.
- Keep T0 = 290 K unless you have a defined reference.
- For cascaded chains, choose stages and enter each stage’s NF and gain.
- Optionally add bandwidth to estimate the input noise power.
- Press Calculate to view results above the form.
- Use the download buttons to save CSV or PDF outputs.
Example data table
| Scenario | Stage 1 (NF / Gain) | Stage 2 (NF / Gain) | Stage 3 (NF / Gain) | Notes |
|---|---|---|---|---|
| Handheld jobsite radio front-end | 3.0 dB / 15 dB | 6.0 dB / 10 dB | 10.0 dB / 5 dB | Good first-stage gain reduces later-stage impact. |
| Receiver with lossy input filter | 2.0 dB / -2 dB | 3.0 dB / 18 dB | 9.0 dB / 8 dB | Front-end loss can dominate total noise figure. |
| Long coax run to a site antenna | 1.0 dB / -4 dB | 2.5 dB / 20 dB | 8.0 dB / 10 dB | Consider moving the LNA closer to the antenna. |
Project notes for receiver noise figure
Noise figure and site reliability
On construction sites, receivers share spectrum with welders, hoists, and temporary generators. A 3–6 dB noise figure is common for rugged handheld or telemetry radios. Each 1 dB improvement in NF increases sensitivity by roughly 1 dB, often turning marginal voice links into dependable coverage around steel and concrete. In planning, pair NF with antenna height to forecast dead zones and place repeaters under cranes, pits, towers, and scaffolds.
Using Friis for multi-stage receivers
Front-end loss matters. A -2 dB filter or long coax run acts like negative gain, so later stages contribute more noise. Friis shows why an LNA placed before losses is valuable: high first-stage gain reduces the (F2−1)/G1 and later terms. Use cascaded mode to compare alternative chains quickly. If stage gain is uncertain, use conservative values; early losses dominate the total.
Interpreting Te and Tsys on projects
Noise temperature converts NF into an input-referred quantity. With T0 at 290 K, an NF of 4 dB corresponds to F≈2.51 and Te≈440 K. System temperature Tsys = F·T0 helps when combining receiver performance with antenna temperature, enclosure heating, or extreme weather planning for outdoor cabinets. Te also helps when datasheets publish noise temperature directly.
Bandwidth and noise floor estimates
Thermal noise rises with bandwidth. When you enter bandwidth, the calculator estimates input-referred noise power using N = k·Tsys·B. For example, at Tsys 600 K and 200 kHz bandwidth, noise power is about -120 dBm. This supports quick checks of required signal levels for digital modems and remote sensors. For 12.5 kHz channels, the thermal floor drops, so interference may dominate.
Documenting results for compliance
Exported CSV and PDF outputs help standardize commissioning notes. Record the mode used, stage assumptions, and bandwidth. Include the measured gain or loss of site cabling, splitters, and lightning protection. A consistent record simplifies troubleshooting when crews relocate antennas, add repeaters, or change channel plans mid-project. Attach exports to daily logs for handovers.
FAQs
Noise figure describes how much a receiver degrades signal-to-noise ratio compared with an ideal device. Lower values mean better sensitivity. It is reported in dB, while the underlying noise factor is a linear ratio.
Friis cascading shows later stages are divided by the gain ahead of them. Strong low-noise gain early in the chain reduces the contribution of mixers, IF stages, and baseband sections to the overall noise figure.
Yes. Treat losses as negative gain in dB. Include input filters, splitters, lightning protectors, and long feedlines. A small loss before the first amplifier can raise total noise figure noticeably.
Use the receiver’s effective noise bandwidth. For digital links, use the channel bandwidth or symbol-rate-based equivalent. For analog systems, use the IF filter bandwidth. If unsure, start with the licensed channel width.
Equivalent noise temperature converts noise figure to kelvin using Te = (F−1)·T0. It is helpful when combining receiver performance with antenna temperature or when comparing microwave equipment specified in kelvin.
Use it when you have measured SNR at the receiver input and output under the same conditions. The difference in dB gives NF directly. This is handy for field checks when internal stage data is unavailable.