Table of Contents
Advertisement
Model 3580A
GENERAL OPERATING INFORMATION
Section III
3-165. X-Axis Output.
The X-AXIS output supplies a de
voltage proportional to the position of the frequency sweep
on the CRT display. When the sweep is at the start
frequency, the X-Axis output is 0 V de; when the sweep is
at the end frequency, the output is + 5 V de. The output
resistance is 1 Kilohm, nominal.
3-166. In the Repetitive and Single sweep modes when
Adaptive Sweep is not used, the X-Axis output is a 0 V to
+ 5 V linear ramp. When Adaptive Sweep is used, the
output voltage tracks the forward and reverse excursions of
the sweep. In the Manual sweep mode, the X-Axis output
voltage corresponds to the sweep position set by the
MANUAL VERNIER control. When the Reset or Log Zero
mode is selected, the X-Axis output remains at 0 V de.
3-167. In the Log sweep mode, the frequency is swept
logarithmically but the X-Axis output is still a 0 V to + 5 V
linear ramp.
An
output of 0 V de corresponds to the 20 Hz
start frequency, an output of + 2.5 V de corresponds to
982 Hz at the center of the display and an output of+ 5 V
de corresponds to the 43 kHz end frequency.
NOTE
Because of the relatively fast sweep rates used
in the Log sweep mode, conventional X-Y
recorders connected to the X-AXIS output
cannot respond properly. To make amplitude
vs. log-frequency recordings, use an X-Y record-
er that has a built-in log converter for the
X-axis input (-hp- 7035B Opt. 020). Connect
the 3580A X-AXIS output to the X-axis input
of the recorder. With the recorder set to the log
mode, sweep the 3580A at a slow linear rate
using the Single or Repetitive sweep mode.
3-168. V-Axis Output.
The Y-AXIS output supplies a de
voltage proportional to the amplitude of the responses
appearing on the display.
An
output of 0 V de corresponds
to the bottom of the screen; an output of + 5 V de
corresponds to the top of the screen. The Y-Axis output
voltage is 0.5 V per division in the Linear amplitude mode,
0.05 V per dB in the Log 10 dB mode and 0.5 V per dB in
the Log 1 dB mode. Output resistance is 1 kilohm nomi-
nal.
3-169. There are several things about the Y-AXIS output
that should be noted:
a. In the Log 10 dB mode, rotating the AMPLITUDE
REF LEVEL control in a clockwise direction offsets the
display in steps of 10 dB. This also offsets the Y-Axis
output in steps of+ 0.5 V.
b. In the Log 1 dB mode, the display ranges from 0 dB
(+ 5 V) to -10 dB (0
V).
The Y-Axis output, however,
extends from approximately + 1 dB (+ 5.5 V) to - 13 dB
(-1.5 V).
c. Changing the baseline threshold using the ADAP-
TIVE SWEEP control does not effect the Y-Axis output
voltage.
3-170. Pen Lift Output.
The PEN LIFT output is provid-
ed for use with X-Y recorders having electrically operated
pen lift circuits that allow the pen to be remotely actuated
by a contact closure. The PEN LIFT output is operative
only in the Single sweep mode. If Adaptive Sweep is not
used, a contact closure is present between the PEN LIFT
output terminals for the duration of the single sweep. If
Adaptive Sweep is used, the contact closure is present only
when the instrument is sweeping slowly over a response.
This prevents the fast-forward and fast-backward excur-
sions of the sweep from being recorded. The PEN LIFT
output terminals are isolated from case ground. Do not
use clear-write to reset sweep.
3-171. Tracking 0 scillator Output.
3-172. The rear panel TRACKING OSC OUT connector
supplies a 5 Hz to 50 kHz sinusodial output signal that
tracks the tuned or swept frequency of the instrument.
The specified frequency response of the tracking oscillator
output signal is
±
3% over the 5 Hz to 50 kHz frequency
range. Total harmonic distortion and spurious is more than
40 dB below a 1 V rms signal level. The output impedance
is 600 ohms, nominal. When the output is terminated in
600 ohms, the LEVEL control may be used to adjust the
output from 0 V to 1 V rms.
3-173. The frequency accuracy of the tracking oscillator
output signal is specified at
±
2.5 Hz relative to the center
of the instrument's passband. On the 1 Hz and 3
Hz
bandwidtns, the passband is less than 2.5 Hz above and
below the center frequency. Thus, the tracking oscillator
output frequency may be slightly outside of the passband.
This is of little consequence except during closed-loop
measurements where the tracking oscillator signal is fed
into the INPUT through a network under test.
If
the
tracking oscillator frequency is outside the passband, inser-
tion loss will be encountered. Under worst case conditions,
maximum insertion loss is approximately 30 dB on the 1
Hz
bandwidth and 8 dB on the 3 Hz bandwidth. Typically, the
insertion loss is about 5 dB on the 1 Hz bandwidth and 2 dB
on the 3
Hz
bandwidth.
3-174. For most closed- loop measurements optimum re-
sults will be obtained using the 10 Hz or 30 Hz bandwidth.
If, for some reason, the 1 Hz or 3 Hz bandwidth is used,
insertion loss can be minimized by removing the top cover
and adjusting A2C4 (100 kHz ADJ) so that the tracking
oscillator frequency is in the center of the passband,
An
alternative approach is to apply an external reference signal
to the TRACKING OSC IN connector and adjust the
frequency of the reference so that the tracking oscillator
frequency is in the center of the passband (see Paragraph
3-176).
3-23
Advertisement
Chapters
Table of Contents
