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Model 5065A
Circuit Diagrams, Theory, and Maintenance
g. On the chassis-bottom side of the unit, note the
short jumper cable connected between J7 and J8 of the
-_
A3 Multiplier.
Disconnect this jumper from A3J8 and
note that the oscilloscope pattern will disappear.
h. Using the Micon-to-BNC test cable provided,
connect a 50-ohm coaxial load to A3J8.
~~
i. At the bottom of the A3 Multiplier is AGC
testpoint A3TP2. Connect a dc voltmeter between this
point and ground. Record the reading. Nominal AGC
_
voltage is about +4.5 volts.
j .
Remove the 50-ohm load from A3J8.
Recon
nect the short jumper cable to A3J8. The oscilloscope
pattern will reappear. Leave the dc voltmeter connected
to A3 TP2 so that the AGC voltage may be monitored
—
NOTE
The following adjustments may peak the
signal at several different points. In tuning
you should select peaks which are fairly
~-
broad and easy to tune.
In addition to
easier tuning, this ensures maximum RF
power stability over the specified operating
_
temperature range of the 5065A.
k. The next step is the adjustment of matching
network adjustments A3C59, A3C61, A3L25, and diode
s ^_ bias adjustment, A3R40. These adjustments are at the
side of the A3 Multiplier Assembly and can be reached
with the A5 Digital Divider removed.
The restricted
space calls for shortened tuning tools. A small mirror
_ will be helpful.
Adjust A3C59, A3C61, A3L25, and
A3R40 for maximum signal on the oscilloscope. Ensure
the AGC voltage does not fall below the value recorded.
If it does, retune these adjustments as necessary.
— During this adjustment, the oscilloscope pattern should
remain rounded at the top. If any clipping or distortion
occurs, the RF drive should be reduced slightly by
adjustment of A3R3.
This adjustment will be reset
~~ later in this procedure.
I. Adjust A3R3 ccw. The pattern on the oscillo
scope screen will get smaller. Continue to adjust A3R3
— ccw with oscilloscope set to .02 V/cm through a 10:1
probe until there is just enough definition at the ends of
the oscilloscope pattern to make a phase adjustment
(typical level .03 V). Now adjust A8R43 so that the ends
—
of the oscilloscope pattern coincide. When this adjust
ment is properly made the oscilloscope pattern will look
similar to Figure 5-10 with the ends of the pattern coin-
v o i d i n g , but with less amplitude. Adjust A3R3 cw until a
phase shift starts (the end of the oscilloscope pattern
just start to split).
m.
Repeat step k to ensure the matching network
\ ^ 1 A 3 C 5 9 , A3C61, and A3L25) and diode bias (A3R40)
^ _
are optimized. RF alignment is complete when (1) A3R3
is adjusted as far cw as possible without a phase shift
_occurring;
(2) A3C59, A3C61, A3L25, and R3R40 are
adjusted for a broad peak and maximum amplitude
signal;
(3) after the preceding adjustments the AGC
voltage is not less than the value recorded in step i; (4)
the signal-to-noise ratio (see Section 5-26) is greater
than 250.
n. Connect HP 302A to A7TP2.
Set HP 302A
MODE SELECTOR to BFO and adjust FREQUENCY con
trol to 137 Hz. Set MODE SELECTOR to AFC; SCALE
VALUE to ABSOLUTE, 300 mV full scale. Read 137 Hz
signal level; typical correct level should be 130 to
160 mV.
o.
Disconnect all test equipment and set OSC
FREQ ADJ FINE to 250.
5-26. Signal-to-Noise Ratio
a. Thistest requires the use of alowfrequency wave
analyzer such as an HP 3581A (if another wave analyzer
is to be used, see step m).
NOTE
The purpose of this test is to insure that the
signal-to-noise ratio of the RVFR, as installed
in the instrument, is sufficient to give the
Model 5065A its specified short-term stability.
This test is not critical to the alignment of the
5065A and may be ignored insofar as align
ment is concerned.
b. Set front-panel controls: OSC FREQ ADJ FINE
at 250, FUNCTION switch . . . at LOOP OPEN.
c.
Connect a dc voltmeter to A8TP3.
d.
Adjust OSC FREQ ADJ COARSE for a reading
of less than ±0.05 volt.
e.
Remove voltmeter from A8TP3.
f.
Set OSC FREQ ADJ FINE at 300.
g.
Set 5381A controls:
POWER
ON
SCALE
VOLTS
AMPLITUDE REF LEVEL
NORMAL
dBv/LIN - dBm
dBv/LIN
INPUT SENSITIVITY
3V (VERNIER TO CAL)
SWEEP MODE
OFF
RESOLUTION BANDWIDTH
10 Hz
DISPLAY SMOOTHING
MAX
FREQUENCY
137 Hz
h.
Connect a 100Kfi resistor across the 3581A input
terminals. Type, tolerance or rating of this resistor is not
important in this application.
i.
Connect 3581A input to A7TP2. Connect 3581A
ground to 5065A chassis. Adjust 3581A FREQUENCY
and INPUT SENSITIVITY for a maximum on-scale read
ing. Record this reading as V
s
. It should be approximately
150 mV.
5-13
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