HP 85020A Operating And Service Manual page 34

Performance Tests
Model 85020A/B
the 8756A, press
[SHIFT] [SCALE]
for the AUTOSCALE function,
then press
[CURSOR] [CURSOR MAX 1]
to find the point of
minimum return loss (the high point on the trace). Record the
displayed CURSOR value on the Performance Test Record, Table
4-1. This value represents the scalar sum of directivity
signals (desired measurement) plus reflected signals from the
fixed load (undesired error). Thus, fixed load quality
directly affects the quality of directivity measurements.
Refer to Figure 4-2. The shaded areas in this figure indicate
the probable range of measurable values for each specified
directivity value. On the horizontal axis, locate the fixed
load's reflection coefficient or its specified return loss
(convert from SWR, if necessarv). Move up from this point to
the upper limit of the shaded area between the diagonal lines.
Enter the value of this upper limit on the Performance Test
Record, Table 4-1. Allowing for the load error, anv
directivity measurement that falls below this limit indicates
that the 85020A/B is probablv within specifications for the
frequency band of interest. If the measurement falls above the
upper limit, the bridge does not meet specifications, and
troubleshooting procedures should be performed.
6. On the 8350A/B Sweep Oscillator, set the START and STOP
frequencies to the next band listed in Table 4-1 (2.4 to 3.0
GHz). Repeat Steps 4 and 5.
Measured
Value
Directivity (p)
(dB)
28.0 .030
31.1 .028
31.7 .026
32.4 .024
33.2 .022
34.0 .020
34.9 .018
35.9 .016
37.1 .014
38.4 .012
40.0 .010
41.9 .008
44.4 .006
48.0 .004
54.0 .002
oo 0
oo
54 48 46
44.4 43.1 42 40.9
(Return Loss)
Specified p or Return Loss of Load
Figure 4-2. Probable Range of Measurable Directivity Values
4-4