Tektronix 492 - Page 22

24
25
26
2-10
REFERENCE LEVEL - a continuous control that
requests
the
microcomputer
to
change the
reference level
one step
each time
the
control is
moved one detent . The normal steps are 10 dB in
the 10 dB / DIV vertical display mode and 1 dB in
the 2 dB / DIV mode . When the vertical display is
changed
to LIN
, the
reference
level
remains
the
same , but can be changed in dB steps equivalent
to
a
full - scale
display
( 8
divisions
X
volts /
division ) ;
in LIN
, the
normal
volts /
division
steps
are
a
1-2-5
sequence .
See
FINE
below
for
the fine
reference
level
steps .
UNCAL . This indicator lights when the display
amplitude is
no
longer calibrated ( e.g.
, selecting
a
sweep
rate
that is
not
compatible
with
the
frequency span
/ div and
resolution
bandwidth ) .
LOG and AMPL CAL . These adjustments
calibrate the dynamic range of the display . The
LOG calibrates the logarithmic gain in dB / Div ,
the AMPL calibrates the reference level of the top
graticule line at the top of the screen .
FINE . A
pushbutton
used to
select fine
incremen
tal
steps for the
REFERENCE
LEVEL . The
reference level
does not
change
when FINE
is
a
switched off
even if it
is not at a
normal step
for
the
display
mode .
Vertical
Display Mode
10
dB /
DIV
2 dB / DIV
LIN
27
FINE Increment
1
dB
0.25 dB ( AA mode ) ²
Voltage
equivalent to
1
dB
MIN
NOISE / MIN
DISTORTION
. One of two
algorithms is
selected to
control
attenuator and
IF
gain . MIN
NOISE
( button
illuminated
) reduces
the
noise
level
by
reducing
attenuation 10
dB and
reducing
IF
gain
10 dB
.
MIN
DISTORTION
reduces IM
distortion due
to input
mixer
overload . To
observe any
change , the RF
ATTEN ,
displayed
by the
crt
readout ,
must be 10
dB
higher
than that set
by the
MIN RF
ATTEN
selector .
In MIN DISTORTION mode ( button not il
luminated
)
distortion
is
minimum .
For
AA
mode
description see
Delta A
Mode
under General
Operating
Information
.
492
Operator's
Handbook