SFRA45 User Manual
11-2
dc = 1/2
v(
) d
0
Having computed the true rms and the dc component, the
ac component can be derived from:
rms
2
= ac
2
+ dc
2
=> ac
2
= rms
2
– dc
2
The ac component is also expressed in dB referred to 1mW
into 600
(dBm):
dBm = 20 log (Vac/Vref)
where Vref =
(1mW x 600
)
or 20 log (Iac/Iref)
where Iref =
(1mW / 600
)
The peak measurement is simply the value with the largest
magnitude. Positive and negative peaks are independently
filtered then the result with the largest magnitude is taken
as the peak value.
In order to measure surge conditions, the maximum
instantaneous peak value (unfiltered) is also recorded. It is
important that the device does not auto range while
measuring surge – either set the range to manual or
repeat the test with ranging set to up only. To reset the
maximum, press START.
Crest factor is derived from the peak and rms:
cf = peak / rms
