Emergency Communication Range Calculator

Line-of-sight range grows with the square root of antenna height (1.42 × √height), while effective range only grows with the square root of power relative to a 5-watt reference — both are diminishing-returns relationships, but height is applied before the terrain and band multipliers scale everything down, so a taller antenna raises the whole baseline range that those multipliers act on. This is why the 'Range w/ 100ft antenna' output, which models a repeater or tower mount, is often dramatically higher than your handheld's effective range even at the same power.

Line-of-sight range is the theoretical maximum assuming no obstructions between the two antennas, purely a function of their heights. Effective range multiplies that number by a terrain factor (as low as 0.15 in mountains, since hills and forest canopy absorb or block signal), a power factor, and a band multiplier, so real-world terrain and equipment limitations can cut the theoretical range to a fraction of the line-of-sight figure — this gap is the whole point of modeling terrain separately.

Only HF (band 3) reflects off the ionosphere to enable long-distance 'skip' propagation that can reach hundreds or thousands of miles independent of line-of-sight; FRS, GMRS, and VHF are all effectively limited to line-of-sight distances at the frequencies and antenna heights typical of emergency use. The skip range shown is a rough function of transmit power only, since real skip distance depends heavily on solar activity, time of day, and exact frequency — treat it as an order-of-magnitude indicator, not a reliable link-budget number.

It assumes a typical 2000mAh handheld battery running a duty cycle of 5% transmitting, 5% receiving, and 90% standing by, with each state drawing a different current — transmit draw scales with your entered power (200 mA per watt), while receive and standby draw fixed baseline currents. The weighted average current draw is then divided into the battery capacity to estimate hours of use, so higher transmit power reduces battery life proportionally to how much of your operating time is spent actually transmitting.