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281, 282, 284
Users Manual
6-2
Introduction
Principles of Sweep Operation
All standard and arbitrary waveforms can be swept with the exception of
pulse, pulse-
train and sequence. During sweep all waveforms are generated in DDS mode because this
offers the significant advantage of phase-continuous sweeps over a very wide frequency
range (up to 10
10
:1). However it must be remembered that the frequency is actually
stepped, not swept linearly, and thought needs to be given as to what the instrument is
actually doing when using extreme combinations of sweep range and time.
For DDS operation during sweep all waveforms must be 409
6 points in length; this is the
natural length for standard waveforms but all arbitrary waveforms are expanded or
compressed in software to 4096 points when sweep is turned on. The expansion or
compression leaves the original data unaffected.
Sweep mode is turned on and off by the on or off soft-key on the SWEEP SETUP
scre
en (accessed by pressing the SWEEP front panel key), or by the sweep soft-key
on the MODE screen. In multi-channel instruments two or more channels can be swept
at once but one set of swe
ep parameters applies to all the swept channels.
When sweep is switched on the software creates a table of 2048 frequencies between, and
including
, the specified start and stop values. For sweep times of 1·03 s and above the
sweep will step through all 2048 frequency values. Below 1·03 s, however, the frequency
sweep will contain fewer steps because of the minimum 0·5 ms dwell at each step; at the
shortest sweep time (30 ms) the sweep will contain only 60 steps.
Because any frequency used in sweep mode must be one of the tabled values, the centre
frequency
displayed (see Sweep Range) may not be the exact mid-point and markers (see
Sweep Marker) may not be exactly at the programmed frequencies. The frequency
resolution of the steps will be at its most coarse with wide sweeps at the fastest sweep
rate.
Connections for Sweep Operation
Sweeps are generally used with an oscilloscope or hard-copy
device to investigate the
frequency response of a device. The MAIN OUT is connected to the device input and the
device output
is connected to an oscilloscope or, for slow sweeps, a recorder.
An oscilloscope or recorder can be triggered by connecting its trigger input t
o the
generator’s SYNC OUT socket. This defaults to sweep sync when sweep is turned
on, going high at the start of sweep and lo
w at the end of the sweep. The low period is
sufficiently long to allow an oscilloscope to retrace.
To show a marker on the display instrument the rear panel CURSOR/MARKER OUT
socket should be connected to a second channel. It can also be used in the case of an
oscilloscope to m
odulate the Z-axis. See the Sweep Marker section below for information
on setting the marker frequency. The cursor/marker polarity and level is set up on the
cursor/marker… menu of the UTILITY screen, as described in chapter 14,
System Operations from the Utility Menu.
For triggered sweeps you must provide a trigger signal, either electrically at the front
panel TRIG IN socket, by a remote command or by manually pressing the MAN TRIG
key. The TRIG IN function automatically defaults to external when you select triggered
sweep. A sweep is initiated on the rising
edge of the trigger signal.
The generator does not provide a ramp output for use with X-Y display
s or recorders.
1.888.610.7664 sales@GlobalTestSupply.com
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