Fig. 2-2. Handle positioned to provide a stand for the instrument.
C A U T I O N
T h e T y p e 4 9 1 s h o u l d n o t b e o p e r a t e d w i t h t h e s e
v o l t a g e s e l e c t o r s w i t c h e s i n i m p r o p e r p o s i t i o n s .
Operation of the instrument with incorrect voltages
will either blow the protective fuses or the instru-
m e n t w i l l n o t o p e r a t e p r o p e r l y .
The Voltage Range Selector located on the rear panel
permits the instrument to operate on line voltages above and
below the nominal 115 or 230 volts. Each selection provides
correct regulation through an overlap voltage range into the
next higher or lower range. It is best to select a range with
its center voltage near your nominal line voltage, thus pro-
viding adequate regulation over a plus and minus devia-
tion of the input line voltage.
The following procedure will prepare the instrument for
operation at your average input line voltage:
1. Remove the cover assembly over the selectors by
unscrewing the two cap screws, then pull the cover with the
attached fuses away from the panel.
2. Pull the Line Voltage Selector out and turn the connector
around to plug it back into the correct position.
3. To change the regulating range, pull out the Range
Selector bar, slide it to the desired range and plug it into
the correct position. Select a range which is centered about
the average line voltage to be applied to the instrument.
See Fig. 2-3.
4. Re-install the cover. Make certain the cover fits firmly
against the rear panel, so the line fuses are seated in their
sockets, and tighten the two cap screws.
5. Before applying power to the instrument, check that the
indicating tabs on the switch bars are protruding through
the correct holes for the desired voltage setup.
2-2
Fig. 2-3. Power panel and selectors.
Spectrum Analyzer Terms
The following glossary of spectrum analyzer terms is pre-
sented as an aid to understanding the terms as they are used
in this manual.
Spectrum Analyzer-A device that displays a graph of the
relative power distribution as a function of frequency, typi-
cally on a cathode-ray tube or chart recorder.
Types: Real-time and non real-time.
A real-time spectrum analyzer performs a continuous
analysis of the incoming signal, with the time sequence of
events preserved between input and output.
A non-real-time spectrum analyzer performs an analysis
of repetitive events by a sampling process.
Methods: Swept front end and swept intermediate fre-
quency.
A swept front end spectrum analyzer is a superheterodyne
spectrum analyzer in which the first local oscillator is swept.
A swept IF spectrum analyzer is a superheterodyne spec-
trum analyzer in which a local oscillator other than the first
is swept.
Summary of Contents for 491
Page 4: ...i i Fig 1 1 The Type 491 Spectrum Analyzer ...
Page 24: ...2 16 Fig 2 17 Control set up chart ...
Page 34: ...Fig 3 1 Function block diagram of the Type 491 3 2 ...
Page 42: ...Fig 3 10 Block diagram of the video detector and vertical amplifier 3 1 0 ...
Page 48: ......
Page 53: ...Fig 4 4 Power Supply Circuit board assembly with wiring color code 4 5 ...
Page 54: ...Fig 4 5 Horizontal Display circuit board assembly showing color code to pin connectors 4 6 ...
Page 55: ...Fig 4 6 IF Control board assembly Wiring color code to pin connector 4 7 ...
Page 64: ...Fig 4 20A Tube subassembly removal procedure 4 16 ...
Page 65: ...Fig 4 20B Tube subassembly installation procedure 4 17 ...
Page 68: ...Fig 4 22 Power supply board assembly with component call out 4 2 0 ...
Page 69: ...Fig 4 23 Vertical Amplifier and Blanking board assembly with component call out 4 21 ...
Page 70: ...Fig 4 24 IF control board assembly with component call out 4 22 ...
Page 71: ...Fig 4 24 IF control board assembly with component call out 4 23 ...
Page 72: ...Fig 4 25 Horizontal display board with component call out 4 24 ...
Page 73: ...Fig 4 25 Horizontal display board with component call out 4 25 ...
Page 74: ...Fig 4 26 Phase lock board with component call out 4 26 ...
Page 88: ......
Page 90: ...Fig 6 1 Test equipment recommended for calibration of the Type 491 6 2 ...
Page 138: ......
Page 192: ......
Page 195: ...SECTION II B 3 ...
Page 196: ......
Page 200: ......
Page 201: ...SECTION 9 DIAGRAMS MECHANICAL PARTS LIST ILLUSTRATIONS ACCESSORIES ...
Page 202: ......
Page 203: ...9 1 ...
Page 204: ...9 3 ...
Page 205: ...9 5 ...
Page 206: ...9 7 ...
Page 207: ...9 9 ...
Page 208: ...9 11 ...
Page 209: ...9 13 ...
Page 210: ...9 15 ...
Page 211: ...9 17 ...
Page 212: ...9 19 ...
Page 213: ...9 21 ...
Page 214: ...9 23 ...
Page 215: ...9 25 ...
Page 216: ...9 27 ...
Page 217: ...FIG 1 9 29 ...
Page 218: ...FIG 2 REAR 9 31 ...
Page 219: ...9 33 FIG 3 IF CHASSIS PHASE LOCK ASSEMBLIES ...
Page 220: ...FIG 4 POWER CHASSIS 9 35 ...
Page 221: ...FIG 5 TIME DIV SWITCH OSCILLATOR ASSEMBLIES 9 37 ...
Page 222: ...FIG 6 CRT SHIELD ASSEMBLY 9 39 ...
Page 223: ...FIG 7 CABINET ASSEMBLY HANDLE 9 4 1 ...
Page 224: ...FIG 8 491 STANDARD ACCESSORIES FIG 8 491 STANDARD ACCESSORIES 9 43 ...
Page 225: ......
Page 226: ...PIN 028017 000 ...