Filter
Top Products
Theory of Operation
2715 Spectrum Analyzer Service Manual
3-93
The Horizontal Display circuit is a paraphase amplifier. Gain and DC offset
(Horizontal Position) are set so the signal at the input of the paraphase amplifier
swings from --1 V to +1 V. The output of the paraphase amplifier then drives the
horizontal deflection plates.
Two signals may be applied to the Horizontal Display circuitry:
H SWP (Sweep from the Sweep board)
H DSHOR (from the Display Storage board)
When an active signal is displayed in normal mode, the horizontal drive signal is
the sweep (SWP), and the vertical drive signal is the detected video (LOGVID);
when a stored signal is displayed, the horizontal drive signal becomes DSHOR
from the Display Storage board, and the vertical drive signal becomes DSVER
from the Display Storage board.
When the video monitor mode is enabled, the vertical signal is a vertical scan
signal (VIDVERT) and LOGVID and DSVER are switched out. At the same
time DSHOR is also switched out, and the sweep signal (SWP) is set to a TV
line rate. A third signal, VIDZ (live video), is routed to the Z Axis circuit.
The Z Axis circuits receive signals from the Display Storage and Sweep boards
and accept control levels from the front panel INTENSITY control. These
signals are then used to control the CRT beam brightness by modifying the CRT
control grid voltage.
VIDZ from the sweep board and /CRTINTS from the Front Panel are summed
into the Z Axis drive amplifier. Two gates also drive the amplifier: /DSBLANK
during readout display periods and SWPGATE during sweep display periods.
The Z Axis clipper circuit consists of two series diodes, plus associated
components. The voltage that passes the clipper circuit is coupled through a
capacitor to the Z Axis rectifier.
The clipped Z Axis drive signal is rectified by a pair of diodes. The rectified
voltage is then fed to the grid of the CRT. A capacitor couples fast changes of the
drive voltage to the grid to speed up the response of the grid circuit. The CRT
grid is protected from high voltage arcs by a spark gap (E110). Also, a 4.75 kΩ
resistor at the junction of the clipper diodes protects the rectifier diodes from
high voltage surges in case the CRT arcs. Clamp diodes CR200 and CR201
protect the Z Axis amplifier from high voltage transients.
Horizontal Display
Z Axis