Logarithmic Addition Of - HP 654A Operating And Service Manual

Model 654A Section V
TEST OSCILLATOR
hp6544
63.-B-1900
10 MHz
LOW PASS
FILTER
SEE FIGURE 5-12
AC VOLTMETER
hp400E
5011 FEED—THRU
TERMINATION
hp11048C
Figure 5-11. Hum and Noise Check
c. Adjust the 654A AMPLITUDE control for an ac
voltmeter indication of OdB on the OdB range.
IN THE FOLLOWING STEP THE 654A
TUNER CAPACITOR IS SHORTED TO
GROUND. CARE SHOULD BE TAKEN
NOT TO TOUCH OR DAMAGE THE
PLATES OF THE TUNER CAPACITOR
OTHERWISE THE INSTRUMENT WILL
HAVE TO BE RECALIBRATED.
DO NOT MOVE THE TWO WIRES BE-
TWEEN TUNER AND RANGE SWITCH
(95 AND 8); THEIR POSITION WILL
EFFECT FREQUENCY. ALL WIRES
ON OR AROUND THE FREQUENCY
RANGE SWITCH CAN EFFECT FRE-
QUENCY RESPONSE.
LLI
<LI
LLIt
y
j
03 _1
—
Z
(no
—I>
LL.Ic
r
aa
+1.5
CO—
(/)
1:CCe
W<
+2.5
+2 0
+1.0
+0.5
r.
0
0 - 2 - 4 - 6 - 8 - - 2 - 4 - 16
DECIBEL DIFFERENCE BETWEEN TWO VALUES
Figure 5-12. Logarithmic Addition of Harmonic Components
d. Remove the 654A top cover: insert a screwdriver
between the tuner capacitor (point X on Figure
5-14) and chassis ground. The residual hum and
noise indicated on the ac voltmeter should be
greater than 70dB below the OdB reference.
Figure 5-13. 10MHz Low Pass Filter
e. If the tolerance is not met ensure that a good
ground connection was made in step d before
troubleshooting the instrument.
5-37. COUNTER OUTPUT CHECK.
a. Set the 654A controls as follows:
FREQUENCY dial 1
FREQUENCY RANGE X10
b. Connect an ac voltmeter to the 654A rear panel
COUNTER OUTPUT; terminate the the cable to
the ac voltmeter with a 50 ohm feedthrough
termination.
c. Sweep the FREQUENCY dial slowly from 1 to 10
for all positions of the FREQUENCY RANGE
switch.
5-11