HP 654A Operating And Service Manual page 37

Model 654A
Section V
TEST OSCILLATOR
hp654A
654A-8-1902
I DB/STEP
ATTENUATOR
hp
355C
THERMAL
CONVERTER
hpl 10504
e
n:
DC NULL
VOLTMETER
hp
4194
O O
r
-
® REFERENCE I
0 SUPPLY
I
SEE FIGURE 5-4 I
Figure 5-16. Meter Tracking Adjustment
i. Check the 654A meter tracking as follows:
1) Set the external attenuator to - 1dB position
and adjust the 654A AMPLITUDE control for
null indication on the dc null voltmeter; the
654A meter should indicate 0 +/-0.05dBm.
2) Set the external attenuator to 0 dB position
and adjust the 654A AMPLITUDE control for
null indication on the dc null voltmeter; the
654A meter should indicate - 1 ± 0.01 dBm.
3) If the tolerances in steps 1) and 2) are not met
then readjust A3R7 ( Meter Offset Cal) as in
step c and repeat steps d through i of this
paragraph.
j. The meter tracking adjustment is completed by
performing Paragraph 5-60.
k. For troubleshooting information refer to Para-
graph 5-94.
5-60. AMPLITUDE CONTROL AND METER
CALIBRATION.
NOTE
Perform adjustments of Paragraph 5-59
before making the following adjustments.
a. Connect the equipment shown in Figure 5-1 using
the 50 ohm termination.
b. Set the 654A controls as follows:
FREQUENCY dial 1
FREQUENCY RANGE X1K
OUTPUT LEVEL dBm + 10.0
IMPEDANCE 50 UNBAL
c. Adjust the 654A AMPLITUDE control for an
indication on the ac differential voltmeter of
.7071V rms (+ 10dBm); adjust A3R7 (Meter Offset
Cal) for a 654A meter indication of OdBm.
d. Set the 654A AMPLITUDE control to the extreme
clockwise position and adjust A3R20 ( Amplitude
Cal) for an ac differential voltmeter indication of
0.80V rms ( approximately + 11.05dBm).
e. For troubleshooting information refer to Para-
graph 5-95.
5-61. AMPLITUDE ACCURACY CALIBRATION.
a. Perform the Amplitude Accuracy checks of
Paragraphs 5-9 through 5-14 but do not make any
adjustments except as outlined below. If the +/- 1%
limits are met for all impedances do not perform
the remaining steps of this Paragraph.
b. If the +/- 1% limits are not met for any impedance:
1) Verify that the impedance networks on the
Impedance Selector board ( A4) have the
correct impedance and if necessary replace any
faulty resistors. The impedance can be checked
by measuring the open circuit voltage ( for each
impedance) which should be twice the
terminated voltage; alternatively set the
attenuator to -80dB position and measure the
output impedance with an ohmmeter.
2) Perform procedure of Paragraph 5-60 except, in
step c (of 5-60) adjust the 654A AMPLITUDE
control for an ac differential voltmeter
indication slightly higher or lower than 0.707V
rms (see example below) so as to correct any
error noted in step a of this Paragraph ( 5-61):
the offset from 0.707V rms should be as small
as possible, but in any case, must remain within
the limits of 0.700 to 0.714V rms.
5-17