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Fig. 6-42. Typical equipment setup to check response flatness, sensitivity, frequency calibration and phase lock operation for band C.
A secondary or alternate source of accurate fre-
quency markers is the combination of two calibra-
tion fixtures (Harmonic Generator 067-0594-00
and a 200 MHz Trap 067-0595-00) and a rela-
tively low frequency, accurate (at least 0.1%)
signal source such as a Time-Mark Generator (Type
184).
The harmonic generator will produce sufficient
harmonic signal power, from the Type 184, to pro-
duce frequency markers into the GHz range. The
200 MHz trap attenuates the IF feedthrough spuri-
ous response.
This procedure is divided into two steps, with step
38B describing the dial check procedure using the
harmonic generator.
a. Equipment setups are shown in Fig. 6-41 through 6-43.
Fig. 6-45 shows the setup for the alternate procedure to check
dial accuracy (step 38 B),
b. Apply a frequency and amplitude calibrated signal,
between -60 dBm and -30 dBm, to the appropriate RF
INPUT connector. Switch the Type 491 band selector switch
to the appropriate band.
c. Set the DISPERSION to 500 kHz/div and the RESOLU-
TION control for a resolution bandwidth of 100 kHz (fully
clockwise).
d. Adjust the GAIN control for an average noise ampli-
tude of one division. Center the IF CENTER FREQ and FINE
RF CENTER FREQ controls.
e. Tune the signal on screen with the RF CENTER FRE-
QUENCY control. Reduce the signal amplitude with the
signal generator output attenuator control for an on-screen
display, then adjust the MIXER PEAKING control and sweep
rate for optimum signal amplitude. (Sweep rate 5 ms/div
or slower.)
f. Calibrate the signal generator output, then adjust the
variable output attenuator control on the signal generator
until the signal amplitude is two divisions (twice the noise
amplitude). See Fig. 6-44.
g. Check the total signal attenuation (in dB) below 0 dBm
as indicated on the signal generator attenuator dial. This
is the sensitivity of the analyzer for the RF center frequency
indicated. Check as listed in Table 6-9 under 100 kHz re-
solution. Sensitivity can also be checked for 1 kHz resolu-
tion, however, a very stable signal source is required at the
higher frequencies. Sweep speed must be rduced to 50 ms/
div or slower to check sensitivity at 1 kHz resolution.
6-41
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 ...