Digitally-Stored Display; Recorder Outputs - HP 3580A Operating And Service Manual

Section III
GENERAL OPERATING INFORMATION
Model 3580A
allow at least 50% of the display range to be used. If the
Adaptive Sweep is not to be used in the Log mode, be sure
the ADAPTIVE SWEEP control is in the OFF position.
3-156. Adaptive Sweep Marker. When the ADAPTIVE
SWEEP control is set to the ON position, a sweep marker
appears on the display. The sweep marker is a blank spot or
gap in the trace that indicates the position of the frequency
sweep. The sweep marker is provided because the digital
memory that generates the display does not track the
fast-forward and fast-backward excursions of the Adaptive .
Sweep. The sweep marker enables the operator to observe
these excursions, making it easy to verify that the Adaptive
Sweep is operating properly.
3-157. In some cases it may be desirable to display the
sweep marker without using the Adaptive Sweep. This can
be done in the linear and Log 10 dB modes by setting the
ADAPTIVE SWEEP control to the ON position and leaving
the baseline threshold at the bottom of the display. With
the baseline threshold at the bottom of the display, the
video level exceeds the threshold level causing the instru-
ment to continually sweep at the panel-selected rate.
3-158. Digitally-Stored Display.
3-159. A unique feature of the 3580A is its digitally-stored
display. The digitally-stored display provides a number of
unusual operating conveniences. For example, display
adjustments are not required when the sweep parameters
are changed. The digitally-stored trace is automatically
cleared and updated at the correct rate. The INTENSITY
and FOCUS controls have the same effect as those of a
regular oscilloscope. Once they are set, they do not need to
be readjusted. Moreover, the INTENSITY control can be
set to any level without danger of burning the CRT face.
Digital storage provides a bright, crips, flicker-free presenta-
tion. There is no blooming of display ambiguity.
3-160. One of the major advantages of digital storage is its
ability to retain a trace indefinitely, i.e., as long as power is
applied to the instrument. When a single sweep is made, the
trace that is generated will continue to be displayed until
the CLEAR WRITE button is pressed or until it is replaced
by a new sweep. If a trace is needed for future reference, it
can be permanently stored in memory by simply pressing
the STORE pushbutton. The "stored trace" and a current
or "refresh trace" can then be displayed simultaneously
(Figure 3-29). If desired, the stored trace can be blanked
from the display by pressing the BLANK STOIIB button.
Releasing the BLANK STORE button returns the stored
trace to the display.
3-161. A permanently stored trace is not effected by
changing the control settings or by pressing the CLEAR
WRITE button. The only way the stored trace can be
cleared from memory is by releasing the STORE button or
turning the power off. When the STORE button is initially
released, the stored trace disappears and a series of dots
appear on the display (Figure 3-30). The dots are automati-
cally cleared when the display is updated by a new sweep.
3-22
STORED
TRACE
Figure 3-29. Stored Trace and Current Trace Displayed
Simultaneously.
3-162. Reduced Resolution. The digital memory in the
3580A has 1024 addresses where the Y-axis amplitude
information is stored. When the STORE button is not
pressed, each address corresponds to a given position of the
frequency sweep and the X-axis of the display is divided
into 1024 discreet segments. When the STORE button is
pressed, the memory is split in half. One half (512
addresses) is used for the stored trace and the other half is
for the refresh trace. Since only 512 addresses are used for
each trace, the display resolution is decreased. This means
that the display is not quite as detailed as it is with a single
trace stored in 1024 addresses. The techniques used for
storing information and splitting the memory are such that
the peaks of the responses are always retained. Thus, the
reduced resolution does not normally obscure any useful
information.
Figure 3-30. Store Button Released.
.3-163. Recorder Outputs.
3-164. Recorder outputs are provided on the rear panel of
the 3580A to permit the use of an external X-Y recorder/
plotter. The -hp- Model 7035B Option 020 X-Y Recorder is
recommended. Although the Standard Model 7035B and
other X-Y recorders can be used, the 7035B Option 020 is
preferable because it has some special features that simplify
scale calibration. In addition, the Model 7035B Option 020
is equipped with an X-axis log converter which can be used
to scale the 3580A linear sweep to obtain a full log sweep
over a 3-decade (10 Hz to 10 kHz) range.