Tektronix 492, 492P, Руководство по обслуживанию

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Calibration—492/492P Service Vol. 1 (SN B030000 & up)
Adjustment Procedure
g. Adjust 2nd LO Sweep
1) Set the front panel controls as follows:
FREQUENCY RANGE
FREQUENCY
FREQ SPAN/DIV
AUTO RESOLUTION
Vertical Display
REF LEVEL
MIN RF ATTEN
5.4— 18 GHz (Band 4)
6.0 GHz
20 MHz
Activated
10 dB/DIV
— 10 dBm
20 dB
2) Connect the comb generator to the RF INPUT and
apply
1 0
ms markers from the time-mark generator
to the FM Input of the comb generator. Adjust
PEAKING (Option 1 instruments) to maximize the
amplitude of the comb markers.
NOTE
If a signal cannot be located at 6.0 GHz with Option 1
instruments, check preselector tracking, step 18.
3) Adjust REF LEVEL and FREQUENCY to display
and center the 6.0 GHz comb line, then reduce
FREQ SPAN/DIV progressively to 100 kHz while
keeping the 6.0 GHz signal centered on the
display.
4) Adjust the 2nd LO Swp, R1067, (Fig. 3-31) on the
Span Attenuator circuit board, so the two comb
lines near the graticule edges are
8
divisions
(800 kHz) apart.
5) Disconnect and remove the comb generator and
time-mark generator from the RF INPUT. Return
the FREQUENCY RANGE to band 1.
6. Check 2nd LO Frequency and Adjust Tune
Range
The procedure applies to both versions of the 2nd LO. An
alternate procedure is also described for use with the
programmable 492P over the GPIB bus.
refer to the Maintenance section for repair. If your in­
strument has the Cavity 2nd LO (B039999 and below)
proceed with the following adjustment.
a) Using a 5/16 inch open-end wrench and a 5/64 inch
, Allen wrench, loosen the lock nut and adjust the
Fine Tune slug in the cavity (Fig. 3-32B) for a
counter reading of 2182.0 MHz.
Do not adjust the two slotted slugs. These are
Varactor diode mounts.
b) Tighten the lock nut and recheck the oscillator fre­
quency. If correct, disconnect the counter and pro­
ceed with part b.
b. Adjust tuning range of the 2nd LO as follows:
1) On the Center Frequency Control circuit board, center
the Fine Tune Range, R4040, and the Fine Tune Sen­
sitivity, R3040, adjustments (see Fig. 3-33).
2) Set the FREQUENCY TO 5 MHz, FREQ SPAN/DIV to
100 kHz, REF LEVEL to +10 dBm and MIN RF
ATTEN to 10 dB. Apply 2 με markers from a time-
mark generator to the RF INPUT.
3) Adjust the FREQUENCY to position a frequency
marker 2.5 major divisions right of center then reduce
the FREQ SPAN/DIV to 50 kHz. Markers should now
appear at the graticule edge.
4) Turn the FREQUENCY control counterclockwise until
the 2nd LO reaches the end of its tuning range (mark­
ers stop moving).
a. Check the 2nd LO frequency as follows:
1) Set the FREQUENCY RANGE to band 1 and FREQ
SPAN/DIV to MAX.
2) Connect a microwave frequency counter, such as
Hewlett Packard 5342A, with a sensitivity of
-2 0 dBm or better, to the 2nd LO Output connector.
3) Measure the 2nd LO frequency. Frequency should be
2182 MHz ±1.0 MHz. If the frequency is not within
this limit, proceed as follows: Instruments that have
the 2182 MHz Phaselocked 2nd LO (B040000 and up)
5) Note the position of the marker signal. If the instru­
ment has digital storage, activate SAVE A to save the
marker reference position.
6
) Turn the FREQUENCY control clockwise and count
the markers as they cross the reference signal loca­
tion until the end of the tuning range is reached. The
9th marker should now be on screen close to the ref­
erence point. Note its position with respect to the ref­
erence established in part 5.
7) If the 9th marker is more than one major division from
the reference, adjust Fine Tune Range R4040 so as to
reduce this distance by one half.