Link Budget Basics
Satellite Communications — Interactive Calculator
A link budget is an accounting of every gain and loss a signal experiences from transmitter to receiver. Engineers use it to answer the fundamental question: does the signal arrive with enough power to carry useful data? The answer is expressed as a link margin — positive means you have headroom, negative means the link fails.
Adjust the sliders below to explore how transmit power, antenna gain, frequency, distance, and data-rate all interact. The chain of equations is always visible so you can see exactly where the margin is won or lost.
Calculator
Governing Equations
Key Insights
At geostationary orbit (∼35,786 km), free-space path loss reaches roughly 205–210 dB at Ku-band — an extraordinary attenuation. To compensate, GEO systems rely on high-EIRP uplinks (large Tx apertures or kilowatt amplifiers) and high-G/T ground terminals. Even a 0.5 dB miscalculation can mean the difference between a working transponder and a failed link.
Doubling the data rate Rb subtracts exactly 3 dB from Eb/N0, cutting margin by the same amount. This is why high-throughput satellites (HTS) at 100+ Gbps aggregate must use aggressive spectral efficiency (high-order QAM, tight frequency reuse) and near-perfect link budgets — there is no free lunch when squeezing bits through a fixed power envelope.
Ka-band (26.5–40 GHz) offers wider bandwidth and smaller antennas, but atmospheric water vapor and rain can add 3–20+ dB of loss that this calculator does not model. Real Ka-band budgets include an “atmospheric margin” and often use adaptive coding and modulation (ACM) to trade data rate for link robustness during storms. Try raising frequency to 30 GHz here and watch FSPL climb — then imagine adding 10 dB of rain attenuation on top.