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c. Note the power reading. Reading, plus the loss
through the filter and pads, must equal
-20 dBm, ±0.3 dB.
3. Signal Substitution Method
NOTE
A power meter is used to verify the output level of the
reference signal. Harmonics of the signal source must
be greater than 40 dB down.
a. Apply a 100 MHz signal from a signal source
(signal generator) through a 3 dB attenuator to
the power meter. Adjust the output level for
-20.0 dBm reading on the power meter.
b. Set the front-panel controls as follows:
FREQUENCY
100 MHz
FREQ SPAN/DIV
500 kHz
RESOLUTION 1 MHz
REF LEVEL
— 10 dBm
TIME/DIV
AUTO
Video Filter Off
Digital Storage VIEW A/B
(Option 02)
PEAK/AVERAGE Fully cw
I
c. Disconnect the meter and (using the same in
strument cable and attenuator) apply the cali
brated reference signal to the 492/492P RF
INPUT.
d. Switch to the 2 dB/DIV display mode and tune
the reference signal to center screen. Select a
REF LEVEL that positions the top of the signal
to a graticule line (2nd or 3rd from the top of the
screen). Select a span/div and resolution
bandwidth to obtain a broad display for more
accurate measurement. If the 492/492P has Op
tion 0 2 , store the reference display by activating
SAVE A.
e. Remove the reference signal and apply the CAL
OUT signal to the RF INPUT.
f. Note the displacement of the CAL signal from
the reference. If the 492/492P has Option 02,
activate B-SAVE A and note the displacement
between the CAL signal and the reference. Dis
placement must not exceed 0.3 dB (0.75 minor
division with a 2 dB/DIV display mode).
NOTE
If greater accuracy is desired, the vertical signal can
be amplified through an external amplifier, such as the
TEKTRONIX 7A15, to increase the vertical sensitivity.
This is done by applying the veritical signal at the rear
panel VERT connector of the 492/492P to the exter
nal amplifier input and selecting the vertical amplifica
tion and Time/Div values that provide the degree of
accuracy desired.
Calibration—492/492P Service Vol. 1 (SN B030000 & up)
Performance Check
4. Check RF Attenuator (within 0.3 dB/10 dB to a
maximum of 0.7 dB over the 60 dB range to 4 GHz;
within 0.5 dB/10 dB to a maximum of 1.4 dB over the
60 dB range to 18 GHz)
NOTE
The attenuator is factory checked to ensure accuracy.
Any change in characteristics should be targe enough
to be readily noticed in operation. The Functional
Check in the Operators manual provides a good indi
cation of attenuator performance and would detect
component failure. External 10 dB, 20 dB, or a 30 dB
step attenuator (calibrated by the user or manufactur
er to within 0.05 dB) must be used as a standard to
check the RF attenuator in this procedure.
a. Test equipment is shown in Fig. 3-3. Apply a 0 dBm,
4 GHz signal, from a signal generator through 30 dB of cali
brated attenuation to the RF INPUT of the 492/492P. Set
the front panel controls as follows:
FREQUENCY RANGE
FREQ SPAN/DIV
AUTO RESOLUTION
REF LEVEL
Vertical Display
TIME/DIV
PEAKING
Band 3 (3.0—7.1 GHz)
200 MHz
On
-30 dBm
10 dB/DIV
AUTO
Max
b. Tune the signal to center screen as the FREQ
SPAN/DIV is reduced to 20 kHz and change the RESOLU
TION BANDWIDTH to 100 kHz. Activate the 2 dB/DIV Ver
tical Display mode and the NARROW Video Filter. Adjust
the signal generator output so the signal peak is at some
graticule reference level, such as seven divisions. If the in
strument has Digital Storage, activate SAVE A.
c. Change the REFERENCE LEVEL 10 dB by switching
to —20 dBm (this will add 10 dB of RF ATTENuation).
d. Remove 10 dB of external attenuation and compare
the difference between the reference level and the new level.
REV JUN 1983
3-11
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