Tektronix 492 - Page 21

(
8
)
memory B are displayed . With Save A mode off ,
all memory locations are displayed and updated
continuously . Data in A memory is interlaced with
data
from B
memory
.
SAVE A - When activated , this mode holds data in
A memory and inhibits further updating . With
SAVE
A
and
VIEW
A
active
,
data in A
memory
is
displayed but not updated , serving as a reference
to compare contents of B memory .
B - SAVE A - When activated , the differential
(
arithmetic
difference
) of
data in B
memory
and
the saved data in memory A is displayed . SAVE A
mode is activated and SAVE A button illuminated .
The zero
difference
point is
nominally
set
at the
middle graticule line with positive differences
displayed above this line and negative
differences
below . ( The
zero
difference
position
on screen is internally switch selectable . )
MAX
HOLD
-
When
activated the
digital storage
memory retains the maximum signal amplitude at
each memory location . This permits visual
monitoring of signal frequency and amplitude at
each memory location over an indefinite period of
23
time . This
feature
is
used to
measure
drift ,
stability , and
record peak
amplitudes
.
PEAK /
AVERAGE - This
control selects
the
amplitude at which the vertical display is either
peak
detected or
averaged
.
Video signals
above
the level set by the control ( shown by a horizontal
line or cursor ) , are peak detected and stored ;
video
signals below the
cursor are
digitally
averaged and stored . See Peak / Average Control
( Digital Storage ) under General Information .
MIN RF ATTEN dB and REFERENCE LEVEL .
These two concentric controls select
the
minimum RF attenuation ( in dB ) between the RF
INPUT and
the first
mixer and the
display
reference
level
respectively .
MIN RF ATTEN dB . Sets the minimum amount of
RF attenuation . Changing REF LEVEL will not
decrease
RF
attenuation below
that set by the
MIN RF ATTEN selector .
Both reference level and actual RF attenuation
(
which may
exceed
the
MIN RF
ATTEN dB
setting ) are
displayed by
the crt
readout .
492 Operator's Handbook
2-9