Tektronix 492 Operator's Handbook

When digital
storage is used , an
additional
quantization
error of 0.5 %
of full screen
must be added
to the
amplitude
performance
characteristics
( i.e.
,
frequency
response ,
sensitivity , etc. ) .
Digital storage memory is functionally divided into two
sections - A and B. Data can be stored in A or B or in both .
There are 512 horizontal locations in A and 512 horizontal
locations in B. When both are displayed , the origin of B is
shifted such that the A and B coordinates are interlaced to
provide 1024 display increments . Data in memory is
continually updated with each sweep so the display , when
viewing A or B , is always current .
When
SAVE Afunction is
activated , data in A
memory
is
held in storage and only B memory is updated . This
inhibition takes place whether A is displayed or not . This
mode captures an event or waveform for comparison with
a subsequent event displayed by VIEW B mode . In this
mode all of A memory is displayed , then all of B , each by a
separate sweep .
When B - SAVE A is activated , the contents of data in B
memory minus the contents saved in A are displayed . This
provides the comparison of the two events by presenting
the algebraic difference of the two displays . This con
venient mode can be used to align filters or other devices
when tuning for a null . The reference waveform is stored in
A and the unknown in B. If the device under test is active ,
@
the B waveform may be larger than the reference which
results in a shift in the zero reference line . The position of
the zero reference can be selected with an 8 - bit digital
switch . The reference level is normally set mid - screen so
positive and
negative quantities can be
observed .
Qualified service personnel can position the reference .
anywhere within the graticule window .
MAX
HOLD
causes
the
digital
memory to be
updated
only if the new input is of higher magnitude than the
former ( B memory only if SAVE A is active ) . This allows
monitoring of signals that may change with time and
provides
a
graphic
record
of
amplitude
/
frequency
excur
sions .
Signal averaging is useful for suppressing noise . The
number of samples averaged per digitized slot ( increment )
is a
function of the
spectrum
analyzer
sweep rate .
The
slower the
sweep speed , the
more
samples
averaged
per
resolution bandwidth . Resolution bandwidth also affects
the amplitude difference between peak detected and
average levels of cw signals . When the resolution
bandwidth is less
than 1 /
30th the
span /
division ( e.g. ,
100 kHz or less with 5 MHz span / div ) there will be
significant
difference
between
peak and
average
amplitude levels of cw signals . The peak value will be the
true value , the
average value will be in
error ,
especially if
only A or B is displayed . It is best to run digital storage with
both A and B
interlaced when using narrow
resolution
bandwidth with
wide frequency
spans
.
492
Operator's
Handbook
3-9

Tektronix 492 Specifications

General

Brand	Tektronix
Model	492
Category	Measuring Instruments
Language	English