Hum And Noise Check 5-1; 10 Mhz Low Pass Filter - HP 654A Operating And Service Manual

Section V
Model 654A
TEST OSCILLATOR
hp654A
am
65.- B-1899
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500 FEED-THRU
TERMINATION
hp11048C
DISTORTION ANALYZER
hp
333A
Figure 5-10. Distortion Check
b. Set the 654A controls as follows:
FREQUENCY dial 1
FREQUENCY RANGE X10
OUTPUT LEVEL dBm + 10,0
IMPEDANCE 50 UNBAL
AMPLITUDE Adjust for + 1dBm
on 654A meter.
c. Verify distortion of greater than 40dB below the
fundamental frequency by checking the distortion
at the following frequency settings of the 654A:
1) FREQUENCY dial at 1, 2, 5, 8 and 10 for each
FREQUENCY RANGE switch setting, X10,
X100, X1K, and Xl0K.
2) FREQUENCY dial at 1, 2 and 5 for X1OOK
setting of FREQUENCY RANGE switch.
d. Disconnect the 654A from the distortion analyzer
and connect the 654A to the wave analyzer
(remove 50 ohm feedthru termination).
e. Set the 654A FREQUENCY RANGE switch to
X1M and the FREQUENCY dial to 1.
f. Tune the wave analyzer to 1MHz and note the
level (in dB) of the 654A fundamental frequency
as indicated on the wave analyzer meter.
g. Tune the wave analyzer to the second and third
harmonics of the 654A frequency and record the
difference ( in dB) between the level of each
harmonic and the level of the fundamental.
Calculate the total harmonic distortion
(calculation below) which should be at least 40dB
below the fundamental frequency level.
NOTE
If both harmonics are more than 43dB
below the fundamental, the total
harmonic distortion will be more than
40dB down and it will not be necessary
to make the following calculation.
1) Ascertain the difference between the
two harmonic levels (in dB).
2) Using the chart below (Figure 5-12),
determine the dB to be added to the
largest harmonic level.
3) Add this amount to the largest har-
monic level. This total should be
40 dB below the level in step f.
Example:
If two harmonics with levels of
-42dB and -48dB are measured, the
difference is -48 -(-42)= -6. Observing
the chart this corresponds to an added
level of 1.0dB. Adding this to the
largest harmonic level (-42dB) gives
-42 + 1.0= -41dB.
h. Set the 654A frequency to 5MHz; tune the wave
analyzer to 5MHz and repeat steps f and g to
measure the total harmonic distortion at 5MHz,
which should be greater than 34dB below the
fundamental.
i. Set the 654A frequency to 10MHz; tune the wave
analyzer to 10MHz and record the level indicated
(in dB) on the wave analyzer meter.
J. Tune the wave analyzer to 20MHz and measure
the distortion which should be at least 34dB below
the level recorded in step i.
k. Perform the adjustment of Paragraph 5-51 if the
tolerances are not met.
5-36. HUM AND NOISE CHECK.
a. Connect the equipment shown in Figure 5-11.
Figure 5-13 shows the parts required to build the
10MHz Low- Pass Filter.
b. Set the 654A controls as follows:
FREQUENCY dial Extreme Clockwise
FREQUENCY RANGE X1K
OUTPUT LEVEL dBm + 10,0
IMPEDANCE 50 UNBAL
5-10