English
Menu

What is Free-space path loss (FSPL)?

The rate at which radio power weakens as it spreads out spherically with distance between isotropic antennas in free space with no obstacles or reflections. It is given by L = (4πd/λ)², and in dB it grows by about 6 dB each time the distance doubles and by 20 dB each time it increases tenfold. It is used as the reference propagation loss in link budget calculations.

Japanese name: 自由空間伝搬損失

Free-space path loss (FSPL) appears in 1 practice question across 1 topic, including Wireless Communication Basics.

Field: Wireless Communication Basics

Try it: questions about Free-space path loss (FSPL)

With transmit and receive antenna gains of 0 dBi, which is closest to the free-space path loss when a 2.4 GHz radio wave (wavelength 0.125 m) travels 100 m through free space?

  1. A40 dB
  2. B60 dB
  3. C80 dB
Show answer and explanation

Answer: C. 80 dB

Free-space path loss is the rate at which power weakens between isotropic antennas as it spreads out spherically with distance, given by L = (4πd/λ)². With d = 100 m and λ = 0.125 m, 4πd/λ ≈ 1.0×10⁴, so L = 20·log₁₀(1.0×10⁴) ≈ 80 dB. In dB, the loss grows by about 6 dB each time the distance doubles and by 20 dB each time it increases tenfold. In this formula, at the same distance the loss is larger at higher frequency (shorter wavelength).

Free-space path loss (FSPL) in the explanations

Questions that mention Free-space path loss (FSPL) (1)

  1. With transmit and receive antenna gains of 0 dBi, which is closest to the free-space path loss when a 2.4 GHz radio wave (wavelength 0.125 m) travels 100 m through free space?

Books on Wireless Communication Basics Ad

As an Amazon Associate I earn from qualifying purchases.

Related terms

Beamforming Bluetooth Low Energy (BLE) Direct-conversion receiver Fading Hidden node problem Link budget LPWA (low-power wide-area) MIMO (multiple-input multiple-output) NFC (near-field communication) Noise figure (NF)

Back to the glossary