ThingMagic M5e-Compact - Manual (Page 35)

RF Power Setting
Functionality of the Embedded Modules 35
RF Power Setting
The power setting is calibrated at the factory and parameters are stored in flash memory
to ensure the power output is within +/– 1 dB of the desired setting. The power limits are
set by both hardware limitations and enforced by the firmware.
Power Units
All power values are reported in centi-dBm. Therefore, a power setting of 2500
corresponds to 25 dBm. All power values in the serial interface are specified as unsigned
16-bit integers. A dBm means power referenced to 1mW. Therefore, the conversion from
watts to dBm is:
dBm = 10 log
10
(power in mW)
For example: 0.1W = 100mW = 20dBm and 1W = 1000mW = 30dBm.
Power Calibration
A power calibration event occurs when the Power set point is changed, the Frequency is
changed, or the RF field is turned on. The power calibration routine calibrates the power
within 10 ms.
Note
Power calibration only occurs once when the RF power is turned on. It does
not occur periodically when the RF field is on.
This is not an issue during normal operation, since a frequency hop occurs at least every
400 ms and thermal drift does not affect the power level significantly. However, in CW
waveform mode (Transmit CW Signal), no power calibration occurs unless the power or
frequency is changed. Thus, it is possible to experience thermal drift in this usage if the
unit is left to transmit continuously for a significant period of time.
TX Read Power
The TX read power is used for all non-write commands to tags. This may include, but is
not limited to, commands to read a tag ID and read tag data.The TX Read Power can be
set in two ways: