PowerXpert™ Help : Using the MA24105A : Measurement Factors
Measurement Factors
The following measurement factors may apply.
Multitone Signals
The MA24105A is a True-RMS sensor that can measure very wide bandwidth modulation. The only limitation is the frequency flatness of the sensor. Because the sensor’s sensitivity is not identical for all frequencies and when measuring multitone signals, the frequency entered into the sensor’s application should be the average frequency of all significant tones.
The MA24105A has an error of 0.05 dB for every 100 MHz bandwidth at frequencies between 0.5 GHz and 4 GHz, and an error of 0.5 dB for every 100 MHz bandwidth at frequencies below 0.6 GHz.
Noise and Averaging
To achieve a required reading resolution, particularly at low power levels, averaging is often needed to reduce noise and steady the displayed power reading. Use the noise vs. resolution Table: MA24105A Averaging Table (Forward Average Power) and Table: MA24105A Averaging Table (Forward Peak Power) to determine the number of averages that will typically be required for a given resolution. Alternatively, determine the number of averages through calculation by using the noise specifications and the fact that noise will be proportional to the square root of N, where N is the number of averages.
For example, a CW tone at +25 dBm is to be measured to 0.01 dB resolution. Using Table: MA24105A Averaging Table (Forward Average Power), the required number of averages is seven averages when measuring average power in the forward direction.
The set number of averages applies to both forward and reverse readings.
Settling Time
The MA24105A samples power continuously every 150 ms. The sensor’s front end and digitizer settles completely to a step change in power in this amount of time. However, there is no way to synchronize the sensor’s sampling to any other event, such as a power step or bus request for a measurement. Therefore, the first measurement requested from the sensor after a power step may not be fully settled. To ensure a fully settled measurement when operating the sensor over the bus, wait 150 ms after a power step before requesting the measurement from the sensor. Alternatively, request two measurements from the sensor and discard the first.
If averaging is required as described above, settling time increases by N × sample period, where N is the number of averages and the sample period is the time in milliseconds. The measurement sample period is 150 ms. When operating the sensor over the bus, request N+1 measurements from the sensor, discard the first, and then average the subsequent readings. The settling time is approximately (N+1) × sample period.
Maximum Power
The MA24105A is rated to meet all specifications up to an average input power level of 150 Watts. Although the average power of all signals should be kept at or below this level, time varying and burst signals having peak powers less than 300 W can be measured. To ensure accurate readings, the peak-to-average ratio (PAPR) of signals must be less than 12 dB.
Power in excess of that shown in Figure: Maximum Power Handling Capacity may damage the sensor.
Maximum Power Handling Capacity