Concepts and features
R&S
®
ZNA
118User Manual 1178.6462.02 ─ 29
●
The integration time T
i
controls the change of the controller output based on the
integral of the error over time. If the value is high, the ALC becomes slower. If it is
too low, the ALC can overshoot and thus become unstable.
The proportional and integration terms are summed to calculate the controller out-
put, so there is a tradeoff between the two terms.
T
control
is the (maximum) time the level control is performed – per sweep point. After
it has elapsed, the VNA proceeds with the measurement. T
control
cannot be set by
the user.
The control parameters can be set manually, or selected automatically by the ana-
lyzer. With automatic ALC parameter setting, the control parameters are deter-
mined by the selected ALC bandwidth as shown in the following table.
ALC IF
band-
width
IF filter (analog): normal IF filter (analog): wideband, narrowband
K
r
(dB) T
i
(ms) T
control
(ms) K
r
(dB) T
i
(ms) T
control
(ms)
20 Hz 0.225 9.5 112.5 0.225 9.5 105.57
30 Hz 0.29 7.5 62.345 0.275 7 60.495
50 Hz 0.3 4.5 36.155 0.275 4.5 48.075
100 Hz 0.34 2.5 29.6 0.6 3.5 26.6
200 Hz 0.85 2.5 20.12 0.0043 0.03 20
500 Hz 1.2 2 13.955 0.65 0.75 5.167
1 kHz 0.8 0.5 3.835 0.3 0.25 1.9
10 kHz 0.66 0.042 0.35 0.3 0.025 0.215
100 kHz 0.11 0.0014 0.04 0.315 0.003 0.031
1 MHz – – – 0.177 .001475 0.04
For some test scenarios, an adjustment of the ALC parameters (loop tuning) can
improve the stability and speed of the ALC.
ALC pre-measurement
Since firmware version 2.30 the ALC measurements are performed separately, before
the user-requested measurements with their corresponding source settings. The ALC
measurements are done one after the other, until all sources have a precise level.
The new pre-measurement allows you to use ALC also for mixer, intermodulation, and
group delay measurements. It also induces a more predictable behavior for pulsed
measurements and higher precision for phase coherent source signals.
ALC optimization
To reduce the overall measurement time, the ALC pre-measurements can also be per-
formed in a speed-optimized way. By default this optimization is done if a single source
is using ALC, but not if pulsed or phase coherent source signals are generated.
Basic concepts
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