Agilent Technologies N9010A - Manual (Page 60)

60 Chapter 1
Agilent EXA Signal Analyzer
Power Suite Measurements
d. Expressed in decibels.
e. An ACP measurement measures the power in adjacent channels. The shape of the response versus fre-
quency of those adjacent channels is occasionally critical. One parameter of the shape is its 3 dB band-
width. When the bandwidth (called the Ref BW) of the adjacent channel is set, it is the 3 dB bandwidth
that is set. The passband response is given by the convolution of two functions: a rectangle of width
equal to Ref BW and the power response versus frequency of the RBW filter used. Measurements and
specifications of analog radio ACPs are often based on defined bandwidths of measuring receivers, and
these are defined by their
−6 dB widths, not their −3 dB widths. To achieve a passband whose −6 dB
width is x, set the Ref BW to be x
− 0.572 × RBW.
f. Most versions of adjacent channel power measurements use negative numbers, in units of dBc, to refer
to the power in an adjacent channel relative to the power in a main channel, in accordance with ITU
standards. The standards for W-CDMA analysis include ACLR, a positive number represented in dB
units. In order to be consistent with other kinds of ACP measurements, this measurement and its speci-
fications will use negative dBc results, and refer to them as ACPR, instead of positive dB results
referred to as ACLR. The ACLR can be determined from the ACPR reported by merely reversing the
sign.
g. The accuracy of the Adjacent Channel Power Ratio will depend on the mixer drive level and whether
the distortion products from the analyzer are coherent with those in the UUT. These specifications
apply even in the worst case condition of coherent analyzer and UUT distortion products. For ACPR
levels other than those in this specifications table, the optimum mixer drive level for accuracy is
approximately
−37 dBm − (ACPR/3), where the ACPR is given in (negative) decibels.
h. To meet this specified accuracy when measuring mobile station (MS) or user equipment (UE) within
3 dB of the required
−33 dBc ACPR, the mixer level (ML) must be optimized for accuracy. This opti-
mum mixer level is
−22 dBm, so the input attenuation must be set as close as possible to the average
input power
− (−22 dBm). For example, if the average input power is −6 dBm, set the attenuation to
16 dB. This specification applies for the normal 3.5 dB peak-to-average ratio of a single code. Note
that, if the mixer level is set to optimize dynamic range instead of accuracy, accuracy errors are nomi-
nally doubled.
i. ACPR accuracy at 10 MHz offset is warranted when the input attenuator is set to give an average mixer
level of
−14 dBm.
j. In order to meet this specified accuracy, the mixer level must be optimized for accuracy when measur-
ing node B Base Transmission Station (BTS) within 3 dB of the required
−45 dBc ACPR. This opti-
mum mixer level is
−19 dBm, so the input attenuation must be set as close as possible to the average
input power
− (−19 dBm). For example, if the average input power is −7 dBm, set the attenuation to
12 dB. This specification applies for the normal 10 dB peak-to-average ratio (at 0.01
% probability) for
Test Model 1. Note that, if the mixer level is set to optimize dynamic range instead of accuracy, accu-
racy errors are nominally doubled.
k. Accuracy can be excellent even at low ACPR levels assuming that the user sets the mixer level to opti-
mize the dynamic range, and assuming that the analyzer and UUT distortions are incoherent. When the
errors from the UUT and the analyzer are incoherent, optimizing dynamic range is equivalent to mini-
mizing the contribution of analyzer noise and distortion to accuracy, though the higher mixer level
increases the display scale fidelity errors. This incoherent addition case is commonly used in the indus-
try and can be useful for comparison of analysis equipment, but this incoherent addition model is rarely
justified. This derived accuracy specification is based on a mixer level of
−14 dBm.