Measurements
R&S
®
FSW
139
User Manual 1173.9411.02 ─ 19
●
Fast ACLR
(Zero-span method ), i.e. using a channel filter
IBW method
When measuring the channel power, the R&S
FSW integrates the linear power which
corresponds to the levels of the measurement points within the selected channel. The
signal analyzer uses a resolution bandwidth which is far smaller than the channel
bandwidth. When sweeping over the channel, the channel filter is formed by the pass-
band characteristics of the resolution bandwidth.
Fig. 5-20: Approximating the channel filter by sweeping with a small resolution bandwidth
The following steps are performed:
1. The linear power of all the trace points within the channel is calculated.
P
i
= 10
(Li/10)
where P
i
= power of the trace pixel i
L
i
= displayed level of trace point i
2. The powers of all trace points within the channel are summed up and the sum is
divided by the number of trace points in the channel.
3. The result is multiplied by the quotient of the selected channel bandwidth and the
noise bandwidth of the resolution filter (RBW).
Since the power calculation is performed by integrating the trace within the channel
bandwidth, this method is called the IBW method (
I
ntegration
B
and
w
idth method).
Fast ACLR
The integrated bandwidth method (IBW) calculates channel power and ACLR from the
trace data obtained during a continuous sweep over the selected span. Most parts of
this sweep are neither part of the channel itself nor the defined adjacent channels.
Therefore, most of the samples taken during the sweep time cannot be used for chan-
nel power or ACLR calculation.
To decrease the measurement times, the R&S
FSW offers a "Fast ACLR" mode. In
Fast ACLR mode, the power of the frequency range between the channels of interest
is not measured, because it is not required for channel power or ACLR calculation. The
Channel Power and Adjacent-Channel Power (ACLR) Measurement
