Theory of Operation
2715 Spectrum Analyzer Service Manual 3-93
The Horizontal Display circuit is a paraphaseamplifier. Gain and DC offset
(Horizontal Position) are setso 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 maybe applied to the Horizontal Display circuitry:
HSWP (Sweepfrom the Sweep board)
HDSHOR (from the Display Storag e board)
When an active signal is displayedin 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 becomesDSVER
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 setto a TV
line rate. A third signal, VIDZ (live video),is routed to the Z Axis circuit.
The Z Axis circuits receive sig nals from the Display Storage and Sweep boards
and accept control levels from the front panel INT ENSITY control. These
signals are then used to controlthe CRT beam brightness by modifying the CRT
control grid voltage.
VIDZ from the sweep boardand /CRTINTS from the Front Panel are summed
into the Z Axis drive amplifier. Twogates also drive the amplifier: /DSBLANK
during readout display periods andS WPGATE during sweep display periods.
The Z Axis clipper circuit consistsof 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 ofthe 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 voltagearcs by a spark gap (E110). Also, a 4.75 kΩ
resistor at the junction of the clipper diodes protects the rectifierdiodes from
high voltage surges in casethe CRT arcs. Clamp diodes CR200 and CR201
protect the Z Axis amplifier from high voltage transients.
Horizontal DisplayZ Axis