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AN-49-005 (December 23, 2019) M176825 (R95497) File: AN-49-005(J).doc
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3.4
Sweep and Hop functions
The GUI
provides the ability to carry out an automated sequence of attenuations settings,
either a sequential sweep from a start value to a stop value, with a fixed step size (increment or
decrement) and dwell time, or an arbitrary "hop" sequence of attenuation and dwell time values.
3.4.1
PC Control Mode (Sweep & Hop Sequences)
This is the default mode, available on all programmable attenuator models. In this mode, the
attenuation sweep or hop sequence is managed by the GUI so each attenuation value is sent to
the attenuator one at a time, as needed. Since the GUI is managing the sequence it is always
able to display the current attenuation state but each attenuation setting is subject to
communication delays between the PC and attenuator. Communication delays vary by
computer but in practice this dictates a minimum dwell time in the order of 3 ms or more for USB
3.0 connections, or longer with USB 1 or 2 connections (10 - 20 ms is not uncommon for older
computers or slower connections).
3.4.2
High Speed Mode (Sweep & Hop Sequences)
In high speed mode, the attenuation sweep parameters or list of attenuation hop values are
loaded into the attenuator's internal memory. This initial configuration step, along with the Start
and Stop commands from the GUI, are subject to the same communication delays as above but
once executed the timing is controlled by the attenuator's internal reference and no further PC
communication is required. This enables high speed attenuation sequences with dwell times as
low as 600 µs or 400 µs (depending on model). Since the PC communication delays are
significantly longer than this minimum dwell time, the GUI will not be able to display the current
attenuation state in this mode until the sequence is stopped.
Figure 3.4:
Plot of signal when sweeping attenuation 0-40dB in 10 dB steps (scale 2ms/div)
