20
This screen is used to set the sweep mode (continuous; triggered; hold and reset; manual) and
sweep direction.
Successive presses of the
direction
soft
−
key select one of the following sweep directions:
up
start frequency to stop frequency.
down
stop frequency to start frequency.
up/down
start frequency to stop frequency and back to start frequency.
down/up
stop frequency to start frequency and back to stop frequency.
The total sweep time is always that set on the
SWEEP TIME
screen, i.e. for
up/down
and
down/up
operation the sweep time in each direction is half the total. Similarly the total number
of steps is the same for all choices, i.e. there will be half the number of steps in each direction for
up/down
and
down/up
operation. In the sweep mode descriptions which follow the direction
is assumed to be
up
but all modes can be used with all sweep directions.
In
continuous
mode the generator sweeps continuously between the start and stop
frequencies, triggered repetitively by an internal trigger generator whose frequency is determined
by the sweep time setting. At the stop frequency the generator resets to the start frequency after
a delay long enough for an oscilloscope to retrace, for example, and begins a new sweep.
If
sync
is set to
on
(the default) the generator actually steps from the stop frequency to zero
frequency and then starts the next sweep from the first point of the waveform, synchronised to
the (internally generated) trigger signal. This is useful because the sweep always starts from the
same point in the waveform but the waveform discontinuity can be undesirable in some
circumstances, e.g. filter evaluation.
With
sync
set to
off
, the frequency steps directly and phase continuously from the stop
frequency to the start frequency but is not synchronised to the software
−
generated trigger signal.
In
triggered
mode the generator holds the output at the start frequency until it recognises a
trigger. When triggered, the frequency sweeps to the stop frequency, resets, and awaits the next
trigger. If
sync
is set to
on
the frequency resets to zero frequency (i.e. no waveform) and
starts a new sweep at the first point of the waveform when the next trigger is recognised. If
sync
is set to
off
the waveform resets to the start frequency and runs at that frequency until
the next trigger initiates a new sweep.
In
hold & reset
mode the generator holds the output at the start frequency until it
recognises a trigger; when triggered, the frequency sweeps to the stop frequency and holds. At
the next trigger the output is reset to the start frequency where it is held until the next sweep is
initiated by a further trigger. If
sync
is set to
off
the output operates exactly as described
above; if
sync
is set to
on
the frequency actually goes to zero at the start and begins each
new sweep at the first point of the waveform.
For
triggered
and
hold & reset
modes the trigger source can be the internal trigger
generator, an external signal applied to TRIG IN, pressing the MAN TRIG key on the front panel,
or a remote command. The trigger source is selected on the TRIG/GATE SETUP screen, called
by pressing the
gated setup
...
soft-key on the
MODE
screen; refer to the Gate Source
paragraph in the Gated Mode section for further details.
In
manual
mode the whole sweep process is controlled from the
MANUAL SWEEP
screen.
Manual Sweep
Before manual control can be used,
manual
must first be selected on the
SWEEP TYPE
screen, see above. Pressing the
manual
soft
−
key on the
SWEEP SETUP
screen then calls
the
MANUAL SWEEP
screen; if
manual
has not first been set as the sweep type, the
message
manual sweep mode not selected
will be displayed before the
MANUAL
SWEEP
screen is shown. Sweep parameters unique to manual operation are set on the
MANUAL SWEEP
screen and Manual Sweep operation using the rotary control is only possible
whilst this screen is shown.
