Keysight 85024A - Page 45

Performance Tests 5
Keysight 85024A User’s and Service Guide 45
Calculating equivalent power
The probe is usually used as a high impedance device. The compression
specification is given as a voltage (instead of power) because of the wide range of
devices with which the probe may be used. For testing the probe, the probe
adapter is used to make the probe input 50 W. Using this known impedance, an
equivalent power can be calculated.
To find the power level equivalent to the 0.3 peak voltage, perform the following
mathematical steps:
Steps Formula Example
1 Convert the peak voltage into
RMS.?
2 Convert the RMS voltage to a
raw power.
3 Convert the raw power to a
power which is relative to
1 mW.
Divide by 0.001w
4 Convert to dBm. 10(LOGx)
10(LOG 0.9) = –0.458 dBm
[a]
[a] Therefore, as shown in the example, the equivalent power to 0.3 V peak in a 50 W system is –0.458 dBm.
V
pk
1.4142135
---------------------
0.3V
1.4142135
--------------------- 0.212132V
RMS
=
V
2
R
----
0.212132()
2
50W
-------------------------0.0009w=
0.009w
0.001w
-------------- 0.9=