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SECTION3
Operafion
whichever results in better resolution.
Step Width =
Sweep Width (deg)
Step Quantity (de@
The MKR OUT signal is synchronous with the sweep
steps. With an ascending sweep, the MKR OUT signal is
low when the sweep phase is higher than the marker
phase. With a descending sweep, the marker output is
high when the sweep phase is lower than the marker
phase. The deviation between the set marker phase value
an8 the actual output in the MKR OLJT~signal is:
Marker Deviation (Maximum) = &Step Width (deg)
The X DRIVE OUT signal will also change synchronously
as the sweep progresses. Resolution of this output signal
is 8 bits. Therefore, when the sweep step quantity is be-
low 255, the sweep step quantity and the X DRIVE output
step quantity are identical.
3.52
Output Range Mode
The Model 3933A amplitude control (waveform and DC
offset) is handled by a multiplying
D/A circuit and an
output attenuator.
AUTO MODE
In AUTO mode, amplitude and DC offset values control
the attenuator, while the output voltage is determined by
the multiplying
D/A device and the attenuator. These
circuits allow a 3-place resolution for:
l
Amplitude (VP-p and Vrms setting)
l
DC offset
A O.ldBV resolution is provided for the dBV setting.
The use of an attenuator assures a quality waveform out-
put (low distortion and noise, high precision) even when
the output signal is low.
Amplitude and DC offset are combined such that the
cummulative value does not exceed 15 volts. However,
when these ratios become large, the one with the lower
voltage loses quality.
FXD MODE
When the output range mode is FXD, the output at-
tenuator is set to Odb. Thus, even if phase, amplitude and
DC offset are changed, the output reflects a smooth tran-
sition. However, the output does pause briefly for
waveform and AM on/off changes.
Amplituded and DC offset can be set independently, as
long as the cummulative voltage does not exceed the
range of rt15. Amplitude may be set to OVp-p, but Vrms
and dBV units may not be used.
Keep in mind, the amplitude setting is controlled only by
the D/A device, so the smaller the amplitude setting, the
fewer the a number of digits and the worse the resolution.
Also, even though amplitude can be set to OVp-p, the ac-
tual output is not truly zero. The greater the phase angle,
the more this tends to happen.
WAVEFORM
QUALITY
AUTO mode is most effective where precise, low level
output is required, and in cases where changes involve a
wide range in uniform steps.
FXD mode is most effective with continuous output
(waveform and DC offset) or when large DC offsets are
added to low level waveforms, and where uniform
changes range from OV to full scale.
See Figure 3-9 for details concerning DC offset setting
range.
See Figure 3-9 for details concerning AC setting resolu-
tion.
3-33
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