Fig. 2-7. Changing band C Coaxial Mixer to Wave Guide Adapter,
The Mixer Adapter or Coaxial Mixer may be removed from
the input receptacle by turning the retainer ring in either
direction. See Fig. 2-7. To replace either assembly, push the
adapter or coaxial mixer against the spring until the flange
bottoms, then turn until the latch snaps to hold the unit in
place.
Signal input power to the analyzer should not exceed -30
dBm. Signal above this level will overload the 1st mixer and/
or the 1st IF stage and generate spurious signals on the dis-
play. Add at least 10 dB of attenuation to the input when
the signal begins to compress (no increase of signal amplitude
with an increase of signal level). A conversion chart (Fig.
2-8) may be used to calculate input signal level.
CAUTION
Signals stronger than +15 dBm applied to the
input or mixer will damage or burn out the mixer
diodes.
Mismatches between the signal source and the RF INPUT
connectors may be caused by signal source output imped-
ance, long coaxial cables, etc. These mismatches will ad-
versely affect display flatness. When optimum flatness is
desired and signal strength is adequate, a 50
Ω
attenuator
pad of approximately 6 to 10 dB should be added between
the signal source and the input to the mixer. The addition
of the attenuator will minimize reflections and optimize dis-
play flatness.
Three attenuator pads, 10 dB, 20 dB and 40 dB are sup-
plied with the accessories kit, These three attenuators may
be stacked on the N type connector to provide up to 70 dB
attenuation. A support should be provided however, if
more than 2 attenuators and an N to BNC adapter are
stacked on the band A connector. The attenuators are rated
at 2 watts (average).
Fig. 2-8. Volts-dBm-Watts conversion chart for 50
Ω
Ω
i m p e d a n c e .
2-9
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 ...