link-budget diagram
Transmitter
Path
Receiver
Free-Space Pathloss (FSPL)

{{ isFinite(fspl) ? fspl.toFixed(2) : '—' }} dB

Estimated RSSI / RX Power

{{ isFinite(rxPower) ? rxPower.toFixed(2) : '—' }} dBm

Categories: Wireless
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Accurately forecasting radio-link viability demands a rigorous yet streamlined method for translating frequency and distance into expected attenuation. Free Space Pathloss & RSSI Calculator fulfils this need in a single responsive page, quantifying propagation losses before hardware is deployed. Engineering trade-offs become clearer when exact decibel budgets are established at the design stage.

Beyond raw loss calculations, the calculator simultaneously estimates received-signal strength by factoring transmitter and receiver gains, cable losses, and supplementary impairments. Results update instantly as you type, enabling exploration of antenna configurations or path optimisations without laborious spreadsheets. Intuitive unit selectors remove conversion errors between megahertz, gigahertz, metres, and kilometres.

Whether you design Wi-Fi, cellular backhaul, or satellite telemetry, the calculator provides an authoritative baseline for link-budget reviews, compliance inspections, and technical presentations. Embed its outputs into documentation, proposals, or simulations to substantiate service-level commitments. Every decibel remains traceable, supporting defensible decisions throughout the wireless-system lifecycle.

Free Space Pathloss & RSSI Calculator combines empirical formulas with real-time analytics to deliver precise, context-aware link-budget metrics.

  • Implements ITU-R FSPL formula 20 log₁₀ d + 20 log₁₀ f + 32.44 [dB].
  • Calculates RSSI by aggregating gains, losses, and path attenuation.
  • Dual distance units (m, km) with automatic conversion to kilometres.
  • Dual frequency units (MHz, GHz) scaled internally to megahertz.
  • Reactive Vue 3 engine updates outputs on every keystroke.
  • Query-string binding permits bookmarkable, shareable scenarios.
  • Bootstrap 5 layout ensures seamless desktop and mobile usability.
Key Parameters
ParameterSymbolInput UnitExampleDescription
FrequencyfMHz/GHz2400 MHzCarrier or centre frequency
Distancedm/km1 kmLine-of-sight path length
Transmitter PowerPTXdBm20RF output at feeder port
Antenna GainGdBi5Directional gain relative to isotropic
Cable LossLCdB1.5Insertion loss from feeder cable
Additional LossLADDdB3Rain, foliage, or body loss margin 
const fspl = 20 * Math.log10(distanceKm) + 20 * Math.log10(freqMHz) + 32.44;
const rssi = txPower + txGain - txCableLoss + rxGain - rxCableLoss - additionalLoss - fspl;

Follow this structured workflow to obtain reliable FSPL and RSSI figures.

  1. Open Free Space Pathloss & RSSI Calculator in any modern browser.
  2. Enter transmitter Power (dBm) in the Transmitter panel. Tip
  3. Fill Antenna Gain and Cable Loss to complete transmitter characteristics.
  4. Specify Frequency and Distance under Path, choosing appropriate units. Caution Ensure line-of-sight conditions.
  5. Provide receiver-side Antenna Gain and Cable Loss; add any extra losses in Additional Loss.
  6. Review the blue FSPL and green Estimated RSSI cards; refine parameters until the RSSI meets link-budget requirements.

The frequently asked questions below clarify methodology and usage nuances.

How is free-space pathloss derived?

It uses the Friis transmission formula rearranged into decibels, incorporating frequency in MHz, distance in km, and a constant 32.44 that relates units to the speed of light.

Why does RSSI sometimes show “—”?

The dash appears when mandatory inputs are zero or non-numeric, yielding an undefined calculation. Provide positive frequency and distance values to resolve.

Does the calculator support non-line-of-sight models?

No. It assumes unobstructed free-space propagation. Apply terrain or clutter models separately and add their losses in “Additional Loss”.

Are antenna polarisation losses considered?

Not automatically. Insert cross-polar or misalignment penalties into the Additional Loss field for accurate budgeting.

Can I hyperlink a prepopulated scenario?

Yes. All inputs synchronise with the URL query string; copy the address bar to share identical parameters with collaborators.

Resolve common obstacles quickly using the checklist below.

  • Critical: NaN outputs — verify that frequency and distance exceed zero.
  • Unexpectedly high FSPL — confirm unit selectors; GHz values entered as MHz inflate loss by 1 000×.
  • Negative RSSI values stronger than transmitter power — re-check gain/loss signs; gains are positive, losses negative.
  • Query string not updating — ensure browser privacy mode permits URL modification.
  • Layout distortion on mobile — disable browser zoom or rotate device to portrait for optimal view.

Apply these professional recommendations to enhance accuracy and workflow.

  • Profile feeder cables at operational temperature; cold-bench figures understate in-field loss.
  • Allocate 3 dB fade margin for each kilometre at 5 GHz in humid climates.
  • Benchmark alternative antennas by adjusting gain while maintaining identical losses for objective comparison.
  • Embed calculator links in design spreadsheets to automate scenario documentation.
  • Use browser developer tools to export JSON snapshots of query-string parameters for change tracking.

Key terms appear below for quick reference.

FSPL
Free-Space Pathloss; attenuation over unobstructed line-of-sight.
RSSI
Received-Signal Strength Indicator; power at the receiver input.
dBm
Power level referenced to one milliwatt expressed in decibels.
dBi
Antenna gain relative to an ideal isotropic radiator.
Additional Loss
User-defined margin covering environmental or hardware penalties.
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