18
Sweep Operation
General
Principles of Sweep Operation
All waveforms can be swept phase-continuously from 0.2Hz up to the maximum frequency for the
selected waveform. Although the frequency is stepped, not truly swept as in an analogue
generator, the short step interval (100us) gives a close approximation to an analogue instrument
except for the widest sweeps in the shortest time; see the Frequency Stepping Resolution section
for further discussion.
The frequency steps are calculated in real-time using a 2-stage process. Major steps are
calculated every 5ms with full precision; the values calculated follow a linear or log sweep law
depending on the choice made on the
SWEEP SPACING
menu. Within each major step
minor steps are calculated every 100us by linear interpolation for both linear and log sweeps.
Linear interpolation gives a small loss of precision for the minor points of log sweeps but the error
is still less than ±1 digit of the displayed frequency except for the widest sweeps in the shortest
time. The advantage that linear interpolation of the minor points gives is that it is fast enough for
all points (major and minor) to be calculated in real time. This is turn permits Start, Stop and
Marker frequencies to be changed with Sweep still running, making performance much closer to
that of an analogue instrument.
Sweep mode is turned on and off either by the
sweep
soft
−
key on the
MODE
screen
(accessed from the Main menu), by the
on
and
off
soft-key on the
SWEEP SETUP
screen, accessed by pressing
setup
...
on the
MODE
screen, or by the
on
and
off
soft-keys on any of the
SWEEP SETUP
sub-menus. Turning sweep off from any of the latter
menus always returns the operating mode to continuous.
Connections for Sweep Operation. Aux 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 can be triggered by connecting its trigger input to the generator’s AUX OUT; AUX
OUT defaults to
sweep sync
when sweep is turned on.
sweep sync
goes low at the start
of sweep and high at the last frequency step of the sweep; depending on the sweep time set this
should be long enough for an oscilloscope to retrace, for example.
AUX OUT will additionally output a marker pulse if the marker frequency is set within the sweep
frequency range. See Sweep Marker section for setting marker frequency.
For triggered sweeps, a trigger signal must be provided at the front panel TRIG/GATE IN socket
or by pressing the MAN TRIG key or by a remote command.
The generator does not provide a ramp output for use with X
−
Y displays or recorders.
Setting Sweep Parameters
Pressing the
sweep setup
...
soft
−
key on the
MODE
screen displays the
SWEEP SETUP
screen.
SWEEP SETUP off
◊
◊
range…
type…
◊
◊
time…
spacing…
◊
◊
manual…
marker…
◊
