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SECTION 3
Operation
hold mode. In the sweep execution mode, the Model
3933A halts the sweep as long as this input remains low.
If you attempt to start a sweep when this input is low, the
Model 3933A immediately enters the sweep hold mode.
Note that pressing HOLD/RESM
does not resume
sweep operation with the hold signal held low; you must
set SWEEP HOLD IN high to resume the sweep.
SWEEP HOLD IN is internally pulled up to a high logic
level, and sweep operation is not affected when this con-
nector is left disconnected from external signals.
3.5.1
Sweep Phase and Sweep Output
Relationships
Figure 3-10 illustrates how sweep PHASE, MKR OUT,
SWEEP SYNC OUT, and X DRIVE OUT signals change
with time.
The MKR OUT signal is low when the sweep phase is
higher than the marker phase. When the sweep function
is or, the high signal level is maintained even after a sin-
gle sweep is terminated.
The SWEEP SYNC OUT signal goes low during the tran-
sition from the start phase to stop phase. When the sweep
function is, the phase changes at the center point of this
output signal.
The X DRIVE OUT jack supplies a voltage that varies be-
tween OV and 1OV in proportion to the lapse of sweep
time, and according to the direction of the sweep phase.
The X DRIVE OUT signal also varies linearly with time.
The X DRIVE OUT signal varies between OV and lOV,
corresponding directly to the change in direction of the
phase sweep.
Substituting
Marker Phase for Center Phase
Press SI-IIFI CTR to set the center phase to the present
marker phase value. This operation produces the same
result as programming an identical phase with the nu-
meric keys. The marker phase is not affected by this op-
eration.
Changing
Settings During
Sweep Operation
Because of processing execution time in the sweep execu-
tion mode, the Model 3933A may respond to the keys and
GPIB commands more slowly than in other modes. If you
change the sweep range, sweep time, or sweep function
with MODIFY while the Model 3933A is in the sweep
execution mode, the unit will recalculate the new pa-
rameters each time you change the setting, resulting in
slower response.
If you set the sweep range based on center and span
phases, an error may occur depending on the order of pa-
rameter selection, whether or not the Model 3933A is in
the sweep execution mode.
Example:
Assume CTRis set to 0", SPAN is set to 180" and you wish
to change these values to 300 and 90, respectively. If you
try to set the CTR to 300, then the SPAN to 90, an error
will occur because the system sees this as an attempt to
set CTR to 390, which is out of range. It is necessary to set
SPAN to 90 first. Then set CTR to 300.
Number of Steps in a Sweep
Software controls the sweep in the Model 3933A. There-
fore, instrument processing speed and phase shift resolu-
tion (12 bits) are the limiting factors in achieving a
smooth sweep curve, except, of course, in the case of a
stepped sweep operation.
The manner in which the sweep resolution is calculated is
shown below. The definition of "step quantity" is the
number of discrete steps between start phase and stop
phase, for the two linear functions (recipro), and (repeat).
Step width is derived from step quantity, as is shown in
the-following formula.
- -
-
Step Quantity =
Sweep Width (deg)
2
or,
Sweep Time (set) x 2000
x 4096
3-32
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