Tektronix 184, Инструкция по эксплуатации

Страница: 35 / 95

Control settings:
Typ
e
1 84
MARKER SELECTOR
TRIGGER SELECTOR
MARKER AMPLIFIER
H.F. SELECTOR
Test Oscil loscope
Crt controls
Horizontal Display
Sweep Controls
A Time/Cm
Variable
A Triggering Mode
Trigger Slope
A Stability
A Triggering Level
Vertical Plug-In Unit
Volts/Div
Variable
Input Coupling
Vertical Position
.1 p.S
1 p.S
OFF
OFF
Adjust for well focused
display of nominal
brightness
Time Base A
.1 p.SEC
Calibrated
AC
+ Int
Preset
Midrange
As required
Calibrated
DC
Midrange
5.
Check or Adjust Crystal Oscillator
0
Adjusting the crystal oscillator frequency requires an
accurate 1 0 MHz frequency standard or frequency measur­
ing device. The National Bureau of Standards through
transmitting stations at Boulder, Colorado (WWVB), Wash­
ington, D.C. (WWV) or Hawaii (WWVH) provide one menas
of checking the oscillator. Another method could be direct
frequency measurement with an Electronic Digital Frequency
Counter. The two methods are described as follows.
NOTE
Allow a m i n i m u m warm-up time of
2
hours for
the crystal oven to stabil ize, before
attempting
to measure or adjust the osci ll ator freq uen cy.
Method 1
a. Test equ ipment setup is shown in Fig. 6-1 0a.
Calibration-Type 1 84
b. Apply the Type 1 84 .1 p.S markers from the MARKER
OUTPUT connector through a 50
n
coaxial cable and 50
n
termination to the Input connector of the Frequency Counter.
c. Adjust C1 1 on the Type 1 84 for equal drift in both
directions of the frequency as the crystal oven cycles.
d. Remove the cable and termination from the Frequency
Counter.
Method
2
a. Test equipment setup is shown in Fig. 6-1 0b. There
is no direct connection between the Type 1 84 and either the
receiver or the test oscilloscope.
b. Trigger the test osci lloscope internally from the signal
input to the vertical plug-in unit.
c. The oscillator may be calibrated by beating the fre­
quency of the crystal oscillator against the frequency from
National Bureau of Standards broadcasting stations. Tune
the receiver to 1 0 or 20 MHz, whichever is stronger. The
signal of the National Bureau of Standards can be recog­
nized by the clicks which occur once each second. Dur­
ing a portion of each minute a 440- or 1000-cycie tone is
heard. Adjust the test oscilloscope vertical sensitivity (Volts/
Cm switch) during this tone time, for a signal amplitude
of approximately 4 cm. Tune the CW or Beat Note Oscilla­
tor in the communications receiver. Tune the receiver care­
fully until only the 440- or 1 000-cycle tone can be heard,
then turn off the CW or Beat Note Oscil lator.
Install a 50-n terminating resistor on the MARKER OUT­
PUT connector of the Type 1 84 and insert a short (12- to 1 5-
inch) piece of wire in the center conductor of the terminator.
d.
Push
the .1 p.S MARKER SELECTOR switch on the Type
1 84. The short wire will act as a radiator for the .1 p.S
signal and wi ll be received by the communications re­
ceiver. If the signal is too strong from the Type 1 84, it
may block out the signal for the National Bureau of Stand­
ards, so if this occurs shorten the radiating wire from the
Type 1 84 until both signals can be heard.
e. During the time the 440- or 1 000-cycle tone is not
being transmitted from the National Bureau of Standards,
adjust C1 1 in the Type 1 84 for minimum beat note, or for
minimum deflection of the signal on the 'test oscilloscope.
After the crystal oscillator frequency has been adjusted,
do not disturb any of the components in the oscillator cir­
cuit. This adjustment of C1 1 will not affect the adjust­
ment of the other markers since they are timed by this
basic frequency and wi ll follow small changes of the os­
cil lator.
f. Disconnect the test equipment setup from the Type
1 84.
g. Interaction - Will affect accuracy of all marker and
trigger signals.
6-9