Product Manual

291, 292, 294
Users Manual
General
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 truly linearly swept, 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 4096 points in length; this is the
natural length for standard waveforms but all arbitrary waveforms are expanded or
condensed in software to 4096 points when Sweep is turned on. This does not affect the
original data.
Sweep mode is turned on and off either by the
on or off soft key on the
SWEEP SETUP
screen 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 simultaneously.
When sweep is turned on the software creates a table of 2000 frequencies between, and
including, the specified start and stop values. Because any frequency used in sweep
mode must be one of the tabled values, the centre frequency displayed (see Sweep range
below) may not be the exact midpoint and markers (see Sweep marker below) may not be
exactly at the programmed frequency. The frequency resolution of the steps will be
particularly coarse with wide sweeps.
Connections for Sweep Operation.
Sweeps are generally used with an oscilloscope or hard-copy device to investigate the
frequency response of a circuit. The
MAIN OUT is connected to the circuit input and the
circuit output is connected to an oscilloscope or, for slow sweeps, a recorder.
An oscilloscope or recorder can be triggered by connecting its trigger input to the
generator’s
SYNC OUT, which defaults to sweep sync when sweep is turned on.
The sweep sync signal goes high at the start of sweep and remains high for the duration
of the first frequency step.
To show a marker on the display instrument the
SYNC OUT can be set to additionally
output a marker pulse. See Sweep marker below for setting the marker frequency.
For triggered sweeps, a trigger signal may be provided by any of the possible trigger
sources, i.e. internal, external, manual or remote.
The generator does not provide a ramp output for use with X-Y displays or recorders.
Setting sweep parameters
Pressing the SWEEP key (or the sweep set-up soft key on the MODE screen) displays
the
SWEEP SETUP screen:
SWEEP SETUP: off
range… type…
time… spacing…
marker…
6-2