Making Power Measurements In The Field

Increasing data demands are changing the modulation signals in today's communication systems. It is no longer enough to have the ability to measure the power of CW signals. Digitally complex signals such as CDMA, EV-DO, GPRS, EDGE, WCDMA, and WiMAX add complexity to power measurement testing. These signals can have a large crest factor (ratio of peak and average power in dB), and a 10 to 12 dB peak-to-average power ratio is common for Quadrature Amplitude Modulated signals. This amplitude variation puts a constraint on the power meter solutions that can be used to obtain accurate power measurements, especially in the field.

The traditional CW diode detector is no longer the best choice for measuring complex modulation schemes. True RMS sensors provide much better readings for RMS power measurements of these non-constant amplitude modulated standards.

The Need For Accurate Power Measurements

Depending on the application, the accuracy of the power meter solution could have a significant impact on the overall performance, particularly if the output power of a base station must be verified.

The output power transmitted at the base station affects the coverage area. When the BTS (Base Transceiver Station) is installed, the output power is measured and verified. System designers try to optimize the coverage area while balancing trade-offs. More output power leads to greater coverage area but it also can create interference. If the power output is below a minimum limit, the coverage area will be reduced and this could eventually lead to dropped calls and dissatisfied customers.