Fig. 6- 45. Alternate equipment setup that will check dial accuracy, mixer and oscillator operation, and LO phase lock effectiveness.
38B. Alternate Procedure to Check Dial Accur-
acy, Oscillator Mixer Operation and Ef-
fectiveness of Local Oscillator Phase Lock
a. Equipment setup is shown in Fig. 6-45.
b. Apply 100 MHz (10 ns) markers from the marker output
of the time-mark generator through the harmonic generator,
the 200 MHz trap, and the 20 dB attenuator to the band B
RF INPUT connector.
c. Switch the band selector to B. Set the DISPERSION to
2 MHz/div and switch the VERTICAL DISPLAY selector to
LOG.
d. Check the dial accuracy as follows:
1) Tune the RF CENTER FREQUENCY through the band.
Observe the 100 MHz harmonics and their image spurii as
they travel across the screen towards the center and merge
with the IF feedthrough response, as the dial crosses a fre-
quency check paint. The harmonics then separate and move
off the screen. See Fig. 6-46. Maximum error between the
dial readings and frequency check points must not exceed
± (2 MHz + 1% of the dial reading).
2) Adjust the MIXER PEAKING control to optimize signal
amplitude. Note the spectral display of the harmonic genera-
tor signals. Tune the RF CENTER FREQUENCY through the
band, checking for dead spots which could be caused by
either local oscillator failure or mixer malfunction. The MIXER
PEAKING must be peaked at all check points.
e. Check-Local oscillator phase lock operation as follows:
1) Turn the INT REF FREQ control on. Decrease the DIS-
PERSION to 500 kHz/div.
2) Depress the LOCK CHECK button and adjust the FINE
RF CENTER FREQ control to position the display to the center
of the graticule area. Release the LOCK CHECK button.
3) Shift the IF feedthrough rsponse approximately 2 divi-
sions off center with the IF CENTER FREQ control, then tune
the RF CENTER FREQ to any harmonic signal. Depress the
LOCK CHECK button and adjust the FINE RF CENTER FREQ
control to establish a lock mode on the harmonic signal. See
Operating instructions.
4) Decrease the DISPERSION to 50 kHz/div, keeping the
signal centered an screen with the IF CENTER FREQ control.
5) Slowly adjust the FINE RF CENTER FREQ control until
the LO loses its lock. The signal may shift screen when the
LO loses phase lock. Re-establish phase lock by adjusting the
FINE RF CENTER FREQ control to return the signal an screen.
6-44
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 ...