Sub-GHz Transceiver Crystal Passivation under Extended High Current Transmit Pulses
Sub-GHz transceiver crystal passivation prevents drive-level dependency shifts and frequency pulling during extended high-current power amplifier transmit pulses.
868 MHz Band
Meaning
Sub-gigahertz radio frequencies allocated for unlicensed short-range devices in Europe and other regions under ITU Region 1 provide a balance between propagation range and data rates. This spectrum segment, known as the 868 MHz band, accommodates low-power wide-area networks and wireless sensor applications without requiring licensing fees. It extends from 863 MHz to 870 MHz, offering a propagation profile that penetrates walls and obstacles better than higher-frequency alternatives.
Output power is generally limited to 25 milliwatts to prevent interference among co-located devices.
Regulatory Limit
Spectrum management authorities impose strict rules on transmit times and power levels to ensure fair access to shared channels. The 868 MHz band is divided into multiple sub-bands, each governed by specific maximum effective radiated power levels and duty cycles. Manufacturers of smart meters and tracking devices design their transmitter firmware to enforce these boundaries during active operation.
These restrictions govern the physical layer parameters of sub-gigahertz radio modules.
Duty Cycle
Transmit constraints dictate the percentage of time a device can occupy a channel within any one-hour window. In the 868 MHz band, a common duty cycle restriction of one percent means a transmitter can only be active for thirty-six seconds per hour. Wireless network protocols schedule data packets to prevent any violation of these limits.
Packet lengths and transmission intervals must remain within these boundaries to secure CE certification.
Coexistence Constraint
Sharing unlicensed spectrum requires reliable packet error handling and collision avoidance mechanisms in crowded environments. When multiple devices transmit simultaneously, packet loss increases and forces retransmissions. High-density deployments use frequency hopping spread spectrum techniques to distribute traffic across several channels.