Keysight N1913 User Manual page 205

Using U2000 Series USB Power Sensors 7
Accuracy
The value of –12 dBm lies in the lower range of the U2000/1/4A sensor. In
autoranging mode ("AUTO"), the power meter determines the average power level
is below –10 dBm and selects the low power path. However, the peak amplitude
of –6 dBm is beyond the specified, square law response range of the low power
path diodes.The high power path (–10 dBm to +20 dBm) should be used to ensure
a more accurate measurement of this signal. However, range holding in "UPPER"
(the high power path), for a more accurate measurement, results in a considerably
increased number of filtering processes.
Speed and Averaging
The same signal also requires that consideration is given to measurement speed.
As shown above, in autoranging mode the power meter selects the low power
path in the U2000/1/4A sensor. With auto-averaging also configured, minimal
filtering is applied. Values of one to four for average power levels above –20 dBm
are used in the low power path. (Refer to "U2000 Series auto-averaging settings"
on page 198.)
If the range is held in "UPPER" for more accuracy, the measurement is slower.
More filtering is applied due to the increase in noise susceptibility at the less
sensitive area of the high power path. Values of one to 128 for average power
levels less than –10 dBm are used. (Again, refer to "U2000 Series auto-averaging
settings" on page 198.) Manually lowering the filter settings speeds up the
measurement but can result in an unwanted level of jitter.
Summary
Attention must be paid to signals whose average power levels are in the low
power path range whilst their peaks are in the high power path range. You can
achieve best accuracy by selecting the high power path or best speed by selecting
the low power path.
Keysight N1913/1914A User's Guide 205