915 MHz US ISM Band Guide: LoRa, IoT & RF Diagnostics

Core Technical Specifications

center Freq 902–928 MHz (frequency hopping)

modulation FSK / GFSK / LoRa CSS

data Encoding LoRa SF7–SF12, NRZ, Manchester

operating Range 500 m – 15 km (LoRa)

antenna ¼ Wave Monopole (~8.2 cm) or SMA whip

tx Power ≤ 1 W (30 dBm) with spread spectrum / FHSS

bandwidth 125 / 250 / 500 kHz (LoRa)

channel Spacing 64+8 channels for US LoRaWAN

Real-World Devices & Applications

IoT & LPWAN

LoRaWAN sensor nodes (agriculture, smart cities, utilities)
Smart electricity, gas, and water meters (US market)
Asset tracking devices (logistics, fleet management)

Industrial

Wireless process monitoring (temperature, pressure, flow)
Remote telemetry units for oil/gas, water treatment
SCADA wireless links

Reference Circuits & Schematics

LoRa Transceiver — SX1276 at 915 MHz

Same SX1276/RFM95W module used for 868 MHz, configured for US915 frequency plan. The US915 plan uses 64 channels (125 kHz BW) from 902.3–914.9 MHz plus 8 channels (500 kHz BW).

Pin	Description
`VCC (3.3V)`	3.3V supply
`GND`	Ground
`SPI Bus`	MISO/MOSI/SCK/NSS
`DIO0`	Interrupt output
`ANT`	50Ω antenna (8.2 cm ¼ wave)

Circuit Walk-Through

Configuration is identical to 868 MHz — only frequency registers and channel plan change. US915 allows up to 1W TX power with spread spectrum, providing significantly more range than the 25 mW EU limit.

Signal Structure & Waveform Analysis

US915 LoRaWAN Channel Plan

72 channels across the 902–928 MHz band.

Uplink 125 kHz

Ch 0–63

902.3–914.9 MHz, 200 kHz spacing

Uplink 500 kHz

Ch 64–71

903.0–914.2 MHz, 1.6 MHz spacing

Downlink 500 kHz

Ch 0–7

923.3–927.5 MHz, 600 kHz spacing

Timing Notes: 400 ms max dwell time per channel (FCC). LoRaWAN manages frequency hopping automatically.

Analysis & Capture Tips

Verify sub-band config — many US gateways only listen on sub-band 2 (ch 8–15)
Check FCC compliance: max 1W TX, 400 ms dwell time
Use ChirpStack or TTN console for uplink monitoring

Bench Troubleshooting & Repair Guide

1. Regional Configuration

Firmware config review

Ensure firmware is set to US915, not EU868. Wrong region = wrong frequencies. Check library defines (e.g., LMIC: CFG_us915).

2. Sub-Band Selection

Gateway console

Many US gateways (TTN) only listen on sub-band 2 (ch 8–15). Configure LMIC_selectSubBand(1) in code if using TTN.

3. Antenna Match

NanoVNA / Multimeter

Verify 3.3V supply, antenna resonance at 915 MHz (¼ wave ≈ 8.2 cm), SWR < 2:1.

915 MHz US ISM Band