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Free-space path loss
Ideal path loss from frequency and distance.
HB3YAQ · Ajdin HadzicLearning to take awayhttps://hb3yaq.ch/en/tools/free-space
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Formula & context
FSPL = 20 log₁₀(4πdf/c)
The formula describes geometric spreading between isotropic antennas in free space. It uses distance in metres and frequency in hertz.
A worked example
145 MHz over 10 km gives approximately 95.68 dB free-space path loss.
Assumptions & limits
Far-field model without terrain, buildings, ground reflection, atmosphere or ionosphere. It does not guarantee reception or coverage.
Building a radio link budgetUnderstand the reasoning →From reading to experimenting
Free-space path loss
145 MHz over 10 km gives approximately 95.68 dB free-space path loss.
Open example with starting values →Frequency: 145 MHz · Distance: 10 kmBack to the learning article →Then change exactly one value. Compare the result and use the formula to explain why it changes. The model limits below the calculator also apply here.