Tektronix 491 Maintenance Manual page 14

1 M H z M A R K E R S O U T - E X T R E F F R E Q I N - A B N C c o n -
nector that provides 1 MHz marker output signals to cali-
With the INT REF FREQ control in
brate the dispersion.
the OFF position, an external signal between 1 MHz and
5 MHz (1 to 5 V peak to peak) applied to the connector
becomes the reference frequency for phase lock operation.
RF INPUTS-Coaxial connectors which connect through
either a coaxial cable, or (if above 12.4 GHz) a wave-
guide mixer, to the signal source. Band A frequency range
is 10 to 275 MHz. Band B frequency range is 275 MHz to
2 GHz. Band C consists of a coaxial mixer (green label) for
the frequency range 1.5 GHz to 12.4 GHz; or a Wave-
guide Mixer Adapter (black label) which connects through
a two foot cable to one of three external Waveguide
Mixers for the frequency range 12.4 GHz to 40 GHz.
Rear Panel
TRIG IN-A BNC connector to apply external triggering
signals. Frequency range: 20 Hz to 100 kHz, signal ampli-
tude equal to or greater than 0.2 V.
S A W O U T - A 7 0 t o 9 0 m V s a w t o o t h s i g n a l o u t p u t t h a t
is coincident with the analyzer sweep.
RECORDER-Signals on the display may be recorded by
connecting to the RECORDER output. A linear output, equal
to or greater than 4 mV per displayed division amplitude
of signal, in the LIN mode, inta a load impedance of
600 ohms.
FIRST TIME OPERATION
The following procedure demonstrates the basic functions
of the controls and connectors for the Type 491. We recom-
mend this procedure for first time familiarization. Careless
or incorrect operation may damage the instrument.
1. Check input power selector positions at the rear panel.
Correct selector positions for the different input line voltages
are given under Voltage Considerations in this section.
2. Preset the front panel controls as follows:
P O W E R
CRT Controls
I N T E N S I T Y
SCALE ILLUM
F O C U S
A S T I G M A T I S M
I N T E N S I F I E R
P O S I T I O N
(Both centrals)
Time Base Controls
T I M E / D I V
VARIABLE
SLOPE
LEVEL
S O U R C E
2-6
O F F
Ccw
Midrange
Midrange
Midrange
Ccw
Midrange
1 0 m s
CAL
+
FREE RUN
I N T
Analyzer
DISPERSION RANGE
DISPERSION—COUPLED
R E S O L U T I O N
I F A T T E N U A T O R d B
I F C E N TE R F RE Q
F I N E
VIDEO FILTER
VERTICAL DISPLAY
G A I N
R F C E N T E R F R E Q U E N C Y
F I N E R F C E N T E R F R E Q
INT REF FREQ
MIXER PEAKING
3. Connect the Type 491 to a suitable power source and
turn the POWER switch to ON. Allow a few minutes for
the instrument to stabilize.
4. Adjust the INTENSITY control clockwise until a trace
is visible, then adjust the FOCUS and ASTIGMATISM controls
for optimum trace definition.
5. Position the trace to the horizontal center and to the
bottom graticule line of the graticule with the POSITION
controls.
6. Adjust SCALE ILLUM control for the desired graticule
illumination.
7. Apply a signal with an amplitude between -60 and
-30 dBm, from a Signal Generator or other source that is,
within the frequency range of band B, through a coaxial
cable to band B, RF INPUT connector.
N O T E
I f a s i g n a l s o u r c e w i t h i n t h e f r e q u e n c y r a n g e a f
band B is not available, apply the signal to band
A or C and set the band selector to the appropri-
ate band.
8. Adjust the GAIN control for a moderate noise level
(1 division) on the display, then tune the RF CENTER FRE-
QUENCY control through the frequency range. Note that
some of the signals move across the screen at different rates,
and the direction of movement (left to right or right to left)
of the signals is not the same. (See Spurious and Image
Frequency displays later in this section.)
9. Tune the dial with the RF CENTER FREQUENCY control
to the frequency of the applied input RF signal.
1 0 . S w i t c h t h e M I X E R P E A K I N G c o n t r o l f r o m S E A R C H
position to manual, then adjust for optimum signal ampli-
tudes.
1 1 . A d j u s t t h e G A I N a n d / o r t h e I F A T T E N U A T O R d B
switches for a signal amplitude of approximately 6 divisions.
Controls
M H z / D I V
Controls coupled together
a n d i n t h e 1 0 M H z / d i v
position
All switches OFF position
Centered (000)
Midrange
O F F
L I N
C C W
Band B
Centered (approximately
5 full turns from either
extreme position)
Out of the OFF switch
detent in the VARIABLE
position
Fully CCW in the
switched SEARCH position