ADL5920 Formula or Method Query for the Reflectometer

Question

Accepted Answer

Question: 
 A customer developing a reflectometer is requesting guidance on signal level conversion. They are currently using Arduino-based software to acquire raw voltage data (e.g., VRMSR = 43.7 mV ) from the reflectometer. 
 They would like to know whether a standard formula or method exists to convert this voltage measurement into the corresponding RF power level in dBm (e.g., –29.24 dBm ). 
 
 Answer: 
 For best accuracy, customers should calibrate their own device to determine the logarithmic slope and intercept , which are used in a simple formula to convert measured voltage to dBm. 
 This method is detailed in the RF Power and Return Loss Calculation section on page 21 of the datasheet. 
 At 100 MHz, the datasheet provides typical values: a slope of 61 mV/dB and an intercept of 29.8 dBm . Using these, a measured Vrms of 43.7 mV the calculation is -29.8dBm + (43.7mV)/(61mV/dB) = -29.1dBm. 
 
 Note these values may vary, so calibration is advised. Also, accuracy is best within the detector’s linear range (–20 dBm to +30 dBm) . Below –20 dBm, the voltage-to-dBm relationship becomes nonlinear and should be corrected for in the user’s system.

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ADL5920: FAQ