FPV Link Budget & Range Calculator
Compute theoretical and practical line-of-sight range for any FPV video or control link using the Friis equation. Accounts for TX power, antenna gains, receiver sensitivity, system losses and fade margin, plus 60% Fresnel zone clearance for long-range planning.
How far will your FPV link actually fly? This calculator runs the Friis transmission equation on your real setup — TX power, antenna gains, receiver sensitivity, system loss — and tells you both the theoretical line-of-sight range (where signal exactly equals receiver noise floor) and the practical range after a fade margin. It also computes the 60% Fresnel zone radius at the midpoint, which is the obstacle-clearance number you need for true long-range flying over terrain.
curl -X POST https://toolsamurai.com/api/v1/drones-uav/fpv-link-budget-calculator \ -H "Authorization: Bearer sk_live_•••••••••••••••" \ -H "Content-Type: application/json" \ -d '{ "tx_power_mw": 1000, "frequency_mhz": "5800", "tx_antenna_gain_dbi": 2, "rx_antenna_gain_dbi": 8, "rx_sensitivity_dbm": -100, "system_loss_db": 2, "fade_margin_db": 10 }'
The method behind the numbers
Radio range in free space is bounded by the Friis equation. Convert TX power to dBm (P_dBm = 10 × log10(P_mW)), add antenna gains, subtract system loss to get the EIRP. Subtract the receiver sensitivity (a negative dBm value) to get the link budget — the total dB available to spend on path loss.
Free-space path loss grows with both distance and frequency: FSPL_dB = 20 × log10(d_km) + 20 × log10(f_MHz) + 32.44. Solving for the range that consumes the entire link budget gives the theoretical max range. Subtracting the fade margin first gives the practical range — what you can fly to and still expect a clean picture or recoverable telemetry after multipath, body shadowing, and atmospheric loss take their bite.
The Fresnel zone is the volume around the line-of-sight path where reflections can still constructively or destructively combine with the direct signal. For reliable long-range flight you want at least 60% of the first Fresnel zone clear of obstacles — its radius at the midpoint is √(d × λ / 4), and the calculator reports the 60% number for the practical range. If a tree line or ridge intrudes inside that radius, your effective range collapses far short of the theoretical figure.
See it in practice
Typical freestyle setup: dipole on craft, 8 dBi patch on goggles.
- tx_power_mw
- 600
- frequency_mhz
- 5800
- tx_antenna_gain_dbi
- 2
- rx_antenna_gain_dbi
- 8
- rx_sensitivity_dbm
- -90
- system_loss_db
- 2
- fade_margin_db
- 10
Long-range control link with omni TX and 8 dBi yagi receiver.
- tx_power_mw
- 250
- frequency_mhz
- 915
- tx_antenna_gain_dbi
- 2
- rx_antenna_gain_dbi
- 8
- rx_sensitivity_dbm
- -112
- system_loss_db
- 2
- fade_margin_db
- 10
Frequently asked questions
Why is 5.8 GHz so much shorter range than 900 MHz at the same power?
Free-space path loss includes a 20 × log10(frequency) term. Going from 900 MHz to 5.8 GHz adds roughly 16 dB of path loss at the same distance — equivalent to throwing away 40× of your transmit power. That's why control links (ELRS, Crossfire) live at 900 MHz / 2.4 GHz and video lives at 5.8 GHz with a much shorter expected range.
Are these numbers achievable in real flight?
Theoretical range assumes perfect line of sight, no multipath, no body shadowing, perfect antenna pointing, and a noise-free environment — none of which hold in reality. The practical range after fade margin is closer to what you'll see if you fly carefully with a directional antenna. A 10 dB fade margin is the sensible default; 15 dB or more for HD or BVLOS work.
What's the Fresnel zone and do I really need clearance?
It's the elliptical 3D volume around the LOS path where reflections affect the signal. If 60% or more of the first Fresnel zone is blocked by terrain, trees or buildings, expect significant signal loss even with line of sight to the antenna itself. Long-range pilots set up on hilltops or with antenna masts specifically to keep this zone clear over the flight area.
Does this work for ELRS / Crossfire control links?
Yes. Plug in your control TX power (often 100–250 mW for ELRS, 250 mW–2 W for Crossfire), set the frequency to 868 / 915 / 2400 MHz to match your module, and use the published receiver sensitivity (around −108 to −112 dBm for ELRS depending on packet rate). The link-budget math is identical to video.
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