Spectrum Measurements
R&S
®
ESR
227
User Manual 1175.7068.02 ─ 12
2. The powers of all trace pixels within the channel are summed up and the sum is
divided by the number of trace pixels 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
Using Fast ACLR, the R&S
ESR sets the center frequency to the different channel cen-
ter frequencies consecutively and measures the power with the selected measurement
time (= sweep time/number of channels).
The RBW filters suitable for the selected standard and frequency offset are automati-
cally used (e.g. root raised cos with IS 136).
The RMS detector is used for obtaining correct power measurement results. Therefore
no software correction factors are required.
Measurement Repeatability
The repeatability of the results, especially in the narrow adjacent channels, strongly
depends on the measurement time for a given resolution bandwidth. A longer sweep
time may increase the probability that the measured value converges to the true value
of the adjacent channel power, but obviously increases measurement time.
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 sweeptime cannot be used for chan-
nel power or ACLR calculation.
To obtain a high repeatability with short measurement times, the R&S
ESR offers a
"Fast ACLR" mode. In the Fast ACLR mode, the R&S
ESR measures the power of
each channel at the defined channel bandwidth, while being tuned to the center fre-
quency of the channel in question. The digital implementation of the resolution band-
widths makes it possible to select filter characteristics that are precisely tailored to the
signal. In case of CDMA2000, the power in the useful channel is measured with a
bandwidth of 1.23 MHz and that of the adjacent channels with a bandwidth of 30 kHz.
Therefore the R&S
ESR changes from one channel to the other and measures the
power at a bandwidth of 1.23 MHz or 30 kHz using the RMS detector. The power of the
frequency range between the channels of interest is not measured in Fast ACLR
mode, because it is not required for channel power or ACLR calculation. The measure-
ment time per channel is set with the sweep time. It is equal to the selected measure-
ment time divided by the selected number of channels.
Measurements
