Meaning
A programmable adjustment value applied to the reference transmission power of a radio frequency transceiver compensates for hardware path losses or regional power limits. By configuring a transmit power offset, developers ensure that the actual radiated power at the antenna connector matches the target value. This setting is crucial for ensuring compliance with regulatory bodies that enforce strict limits on effective isotropic radiated power.
The offset value is typically stored in the non-volatile memory of the wireless module during production calibration.
Offset Purpose
Compensating for the attenuation caused by internal cables and circuit board traces is the primary objective of the setting. If a board layout introduces a loss of two decibels between the radio chip and the antenna port, a corresponding transmit power offset is applied to boost the internal amplifier output. This adjustment guarantees that the device delivers the expected signal strength to the antenna, maintaining the specified range.
Conversely, the offset can be used to decrease output power to prevent overloading nearby receivers.
Antenna Adaptation
Different antenna designs require specific offset configurations to maintain both regulatory compliance and link budget. High-gain directional antennas radiate power more efficiently in a single direction, meaning the transmit power offset must be adjusted downward to avoid exceeding the maximum regional limits. During the integration of a new antenna, engineers must measure the radiation pattern and calculate the correct offset.
This calculation ensures that the system operates at the highest permissible power level without violating certification parameters. The adjusted values are hardcoded into the device firmware, preventing any unauthorized modification that could lead to illegal operation of the radio.
Handover Document
The final offset values are recorded in the device’s configuration sheet and verified during the end-of-line test. This report serves as a record that each manufactured unit has been calibrated to meet the regional radio frequency standards. The document is often required as part of the technical construction file during regulatory audits to prove compliance.
