MANET Link Budget Calculator

Interactive link budget calculator for military MANET radio systems. Calculate SNR, margin, Fresnel clearance, and maximum range for Silvus StreamCaster at 140-600 MHz.

Interactive: MANET Link Budget & Range Calculator

Free-Space Path Loss and MANET Link Reliability

The link budget calculator determines if the communication path between mesh nodes is viable reliably. The fundamental equation is the Friis free-space path loss formula: FSPL = 20×log10(d) + 20×log10(f) + 32.44, where d is distance in kilometers and f is frequency in megahertz. For the Silvus StreamCaster at 300 MHz over 10 kilometers, the free-space path loss is 102.0 dB. The received power equals transmit power plus antenna gains minus path loss minus environmental losses. If signal strength remains above the receiver sensitivity threshold (-110 dBm) by more than the required SNR (10 dB), the link works. The margin — how many decibels above the minimum threshold — determines reliability in adverse conditions such as rain, vegetation, or multipath interference.

Antenna Selection for Tactical MANET Deployment

The calculator compares three antenna types commonly available for field deployment. Omnidirectional antennas (+2 dBi) radiate equally in all directions — suitable for mobile platforms like vehicles and drones that change orientation. Patch antennas (+6 dBi) concentrate energy in a 60-90 degree sector — useful for ground stations with known direction to the relay drone. Yagi antennas (+9 dBi) focus energy in a 30-45 degree beam — the highest gain option for fixed point-to-point links. Upgrading from omni-to-omni to yagi-to-omni more than extends usable distance at minimal per-unit cost — the most cost-effective range improvement available.

Environmental Loss Factors in Nordic Terrain

Free-space path loss assumes an unobstructed vacuum between antennas. Nordic terrain adds environmental losses: light vegetation (spruce forest with canopy gaps) adds approximately 6 dB of loss, reducing effective range by 50 percent. Dense boreal forest (continuous canopy) adds 15 dB, reducing range by 80 percent. Urban environments (Kiruna, Luleå) add 25 dB. The practical implication: a link that works at 50 kilometers in free space may fail at 5 kilometers through dense forest. This is why the Fischer 26 relay drone at 200 meters altitude is essential — it provides line-of-sight clearance above the tree canopy, eliminating vegetation loss entirely.

Read the full technical documentation →

Multi-Hop Relay Planning for Brigade Operations

A single Fischer 26 at 200 meters altitude provides line-of-sight coverage to approximately 50 kilometers. But the MANET mesh often requires multiple relay hops to reach all units in a brigade-wide deployment spanning 30+ kilometers of complex terrain. Each hop adds 8 milliseconds of latency and reduces available bandwidth by approximately 15 percent due to the half-duplex relay overhead. The link budget calculator helps planners determine the optimal number and positioning of relay nodes. For a typical Norrbotten deployment with rolling terrain and dense spruce forest, three relay hops (four total nodes including source and destination) provide reliable coverage across 25 kilometers with 44 milliseconds total latency and approximately 55 percent of point-to-point bandwidth — acceptable for real-time video streaming and COP updates.

Antenna Polarization and Ground Reflection Effects

The link budget calculator assumes free-space propagation modified by environmental loss factors. In practice, ground reflections create multipath interference that can either strengthen or weaken the received signal depending on geometry. Vertically polarized antennas experience less ground reflection than horizontally polarized ones, making vertical polarization the standard choice for tactical MANET deployments. The Silvus StreamCaster uses circular polarization which provides consistent performance regardless of the relative orientation between transmitter and receiver — essential when one node is a rotating Fischer 26 in flight and the other is a stationary ground station. Circular polarization sacrifices 3 dB compared to matched linear polarization but eliminates the risk of complete signal cancellation from polarization mismatch.

Implementation

# MANET Link Budget — Friis Free-Space Path Loss
import math

def link_budget(tx_dbm, tx_gain, rx_gain, freq_mhz, dist_km, env_loss=6):
    """Calculate received power and SNR margin."""
    fspl = 20*math.log10(dist_km) + 20*math.log10(freq_mhz) + 32.44
    rx = tx_dbm + tx_gain + rx_gain - fspl - env_loss
    snr = rx - (-110)  # noise floor
    margin = snr - 10   # required SNR
    return {"rx_dbm": round(rx,1), "snr": round(snr,1),
            "margin": round(margin,1), "link_ok": margin > 0}

# Silvus SL5200: 33dBm TX, 300MHz, omni antennas
r = link_budget(33, 2, 2, 300, 10, env_loss=6)
print(f"RX: {r['rx_dbm']} dBm | SNR: {r['snr']} dB | Margin: {r['margin']} dB")
print(f"Link: {'OK' if r['link_ok'] else 'FAIL'}")

Sources

• ArduPilot — ardupilot.org
• FOI — FOI publications catalogue (foi.se/publications)