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Why can’t the U2000 Series USB Power Sensors accurately measure the average power of some pulse modulated signals?

The U2000 Series USB power sensors are not able to measure the true average power of pulse modulated signals where the duty cycle is small or the pulse period is very long.

For USB sensors with firmware revision A1.02.00 and A1.02.01: In order to accurately measure the average RF power of a pulsed signal, the pulse signal profile must have the following parameters:

- Duty cycle greater than 40%

- Pulse period greater than 100 microseconds and less than 2 milliseconds

If your pulse profile meets the recommended profile above, then use the following settings to achieve more accurate and repeatable average power measurements:

- Average count of 50 or more

- Step detect OFF

For pulse modulated signals with a duty cycle of less than 40% or a pulse period that is not within the range of 100 microseconds to 2 milliseconds, we recommend that you use the time-gated measurement feature of the U2000 Series USB power sensors, if an externaltrigger signal is available.

For USB sensors with firmware revision A1.03.01 or higher: the pulse signal profile must have the following parameters:
- Duty cycle greater or equal to 1%
- Pulse period less than 8 milliseconds
- Pulse width of greater or equal to 30 us
If your pulse profile meets the recommended profile above, then use the following settings to achieve more accurate and repeatable average power measurements:
- Use the command “SYSTem:PRESet BURST” to set the sensor in the burst mode. The N1918A provides this preset for average pulsed measurements
- Step Detect OFF
- Average count of 256 or more
For other pulse modulated signals we recommend that you use the time-gated measurement feature of the U2000 Series USB power sensors. This feature can use either external or internal triggering. See the U2000 series documentation for more information.
 

U2000 Time-gated feature