915 MHz North American ISM / LoRa Band Engineering Guide & Solvers
FCC Part 15 license-free ISM band for LoRaWAN, RFID, Meshtastic, and SCADA links in the Americas.
Dedicated Calculators Tuned for 915 MHz
915 MHz Wavelength
Compute resonant wavelength element lengths, matching specs, and RF parameter formulas for 915 MHz.
915 MHz Half-Wave Dipole
Compute resonant half-wave dipole element lengths, matching specs, and RF parameter formulas for 915 MHz.
915 MHz Quarter-Wave Vertical
Compute resonant quarter-wave vertical element lengths, matching specs, and RF parameter formulas for 915 MHz.
915 MHz Yagi-Uda Array
Compute resonant yagi-uda array element lengths, matching specs, and RF parameter formulas for 915 MHz.
915 MHz Free Space Path Loss
Compute resonant free space path loss element lengths, matching specs, and RF parameter formulas for 915 MHz.
915 MHz Atmospheric & Terrain Propagation Dynamics
Signals at 915 MHz propagate primarily via line-of-sight space waves, with terrain diffraction and atmospheric refraction determining coverage beyond the optical horizon.
- Free-space wavelength of 0.328 meters (32.8 cm) allows compact, high-efficiency antenna elements.
- Geometric path loss is 91.7 dB at 1 kilometer and 111.7 dB at 10 kilometers in unobstructed free space.
- RF skin depth in copper conductors is 2.18 micrometers, requiring high-conductivity plating on high-power tank circuits.
- Tropospheric bending extends the radio horizon approximately 15% beyond optical line-of-sight under standard 4/3 k-factor atmospheric refraction.
Resonant Antenna Cut Dimensions at 915 MHz
| Antenna Type | Metric Dimension | Imperial Dimension | Workshop & Tuning Advice |
|---|---|---|---|
| Half-Wave Center-Fed Dipole | 0.156 m (0.078 m per leg) | 0.51 ft (0.26 ft per leg) | Includes 0.95 physical end-effect shortening. Cut 3% longer for tuning with an antenna analyzer. |
| Quarter-Wave Ground Plane Vertical | 0.078 m radiator height | 0.26 ft radiator height | Equip with 4 downward-sloping radials (45-degree droop) to match 50 Ohm coax directly. |
| 5/8-Wave High-Gain Vertical | 0.195 m radiator | 0.65 ft radiator | Provides approximately 3 dB of omnidirectional gain with low take-off angle; requires a base series matching inductor. |
Coaxial Feedline Attenuation at 915 MHz (per 100 Feet)
| Coaxial Cable Model | Loss / 100 ft | Power Delivered | Engineering Recommendation |
|---|---|---|---|
| RG-58 (Thin Coax) | 13.3 dB | 5% | Avoid for runs over 15 feet due to high attenuation. |
| LMR-400 (Low-Loss Foam) | 3.0 dB | 50% | Recommended standard for base station antenna feedline runs up to 100 feet. |
| 1/2" Heliax Hardline | 1.4 dB | 72% | Optimal for commercial repeater masts and weak-signal satellite stations. |