Tektronix 492, 492P, Service Manual

Page: 41 / 303

Calibration—492/492P Service Vol. 1 (SN B030000 & up)
Performance Check
TM 503 Main Frame
Comb G e n e r a t o r / ^
/ Source /
ΓΊ
■ □
O
O 0
o
o
FM AM
O O
Digital
Counter
Time
Mark
Generator
492 Spectrum Analyzer
2 7 2 7 - 1 A
Fig. 3-1. Test equipment setup for checking frequency of the calibrator and the accuracy of the frequency readout.
f. Repeat this process checking frequency readout accu­
racy in 1 GHz or 2 GHz increments for bands 1 through 3 (0
to 7.1 GHz) applying the limit ±(0.2% of center frequency
+20% of span/div) above 2.5 GHz.
Tune a comb line (marker frequency) to center screen
with the FREQ SPAN/DIV at 1 MHz. Press DEGAUSS and
recenter the marker if necessary with the FREQUENCY
control. Activate the CAL pushbutton and adjust the FRE­
QUENCY control so the frequency readout equals the re­
quired accuracy at that point, (i.e. If the marker is above the
readout frequency then adjust the readout for a higher read­
ing; for example, the readout for a 2.000 GHz marker would
be moved to read 2.005 GHz with the marker centered.)
Now recheck the frequency readout accuracy to ensure that
the readout is within specifications over the range of the
oscillator tuning.
Since the other bands operate on harmonics of the oscil­
lator fundamental, accuracy or error will be the same as that
measured for the fundamental bands multiplied by the har­
monic number (n) of the band.
If you choose to check the higher bands, it may be nec­
essary to increase the REF LEVEL to —10 dBm to locate
true response of the 500 MHz comb. MIN RF ATTEN should
not be decreased below 10 dB unless the instrument has
the preselector (Option 01). When checking instruments
with the preselector, adjust the PEAKING control for maxi­
mum signal response, when operating above band
1 ( 0
to
1
. 8
GHz), as each signal is tuned to center screen.
g. Leave the comb generator connected for 492P; dis­
connect the comb generator for the 492.
2A. 492P only— TUNE Accuracy Check ±(7% of
frequency or 150 kHz)n, whichever is greater, after a
2-hour warm-up
a. Enter the following program on a 4050-Series
controller:
100 REMARK TUNE CHECK
110 PRINT @1 :"SAVEA OFF;TRIG FRERUN"
120 WBYTE @33,1:
130 INPUT T$
140 PRINT @1 :' SIGSWP;SAVEA ON;TUNE";T$;'';SIGSWP''
150 INPUT W$
160 GO TO 110
b. Connect the 4050-Series controller to the 492P with a
GPIB cable (both should already be turned on). Set the
492P GPIB ADDRESS switches for address 1 (switch 1 up,
all others in the switch bank down).