Aim-TTI TGA1240 Series, Инструкция по эксплуатации

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Sweep Operation
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
). 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 at once but
the sweep parameters are the same for all channels.
When sweep is turned on the software creates a table of 2048 frequencies between, and
including, the specified start and stop values. For sweep times of 1·03s and greater the sweep
will step through all 2048 frequency values. Below 1·03s, however, the frequency sweep will
contain fewer steps because of the minimum 0·5ms dwell at each step; at the shortest sweep
time (30ms) 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 frequency. The frequency resolution of
the steps will be particularly coarse with wide sweeps at the fastest sweep rate.
Connections for Sweep Operation. Sync Out and Trig In
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; SYNC OUT defaults to
sweep sync
when sweep is turned on.
sweep sync
goes high at the start of sweep and low at the end of sweep. At the end of sweep it is low long
enough for an oscilloscope to retrace, for example.
To show a marker on the display instrument the rear panel CURSOR/MARKER OUT socket
should be connected to a second channel. Alternatively, for an oscilloscope the signal can be
used to modulate the Z
−
axis. See Sweep Marker section for setting marker frequency. The
cursor/marker polarity and level is set up on the
cursor/marker
… menu of the UTILITY
screen, see System Operations section.
For triggered sweeps, a trigger signal must be provided at the front panel TRIG IN socket or by
pressing the MAN TRIG key or by a remote command. The function of TRIG IN is automatically
defaulted to external when triggered sweep is selected; a sweep is initiated by the rising edge of
the trigger signal.
The generator does not provide a ramp output for use with X
−
Y displays or recorders.