TM 11-6625-2781-14&P-2
Section III
illuminated more rapidly and the display is obscured.
3-16. If the operator is only interested in measuring
The effective persistence and storage time are thus
amplitude, the signal at the mixer can be as high as -10
considerably reduced.
dBm. (Signals above this level will compress.)
3-22. Photographic Techniques
3-17. Variable Persistence and Storage Functions
3-23. Excellent oscillographic photography is possible
3-18. With the 141T Display Section the operator can
when the Spectrum Analyzer is used with proper optics
set trace persistence for a bright, steady trace that does
and when proper techniques are employed. Both the
not flicker, even on the slow sweeps required for narrow
HP 196B and the 197A Oscilloscope Cameras attach
band analysis. The variable persistence also permits
directly to the analyzer's CRT bezel without adapters.
the display of low repetition rate pulses without flickering
Both cameras also have an Ultra-Violet light source that
and, using the longest persistence,. intermittent signals
causes a uniform glow of the CRT phosphor. This gives
can be captured and displayed. The storage capability
the finished photograph a gray background that
allows side-by-side comparison of changing signals.
contrasts sharply with the white trace and the black
graticule lines. Ultra-Violet illumination is normally
3-19. Persistence and Intensity. These controls
used only when the CRT is of the non-storage and fixed
largely determine how long a written signal will be
persistence type (140T Display Section). For a storage
visible. Specifically, PERSISTENCE controls the rate at
or variable persistence CRT (141T Display Section), a
which a signal is erased and INTENSITY controls the
uniform gray background is obtained by simply taking
trace brightness as the signal is written. With a given
the photograph in STORE rather than in VIEW.
PERSISTENCE setting, the actual time of trace visibility
can be increased by greater INTENSITY. Since the
3-24. APPLICATIONS OF SPECTRUM ANALYSIS
PERSISTENCE control sets the rate of erasing a written
signal, it follows that a brighter trace will require more
3-25. Signal analysis in the frequency domain is
time to be erased. Conversely, a display of low intensity
recognized as a tremendous aid in the evaluation of
will disappear more rapidly. The same principle applies
circuits and systems. Frequency<lomain techniques are
to a stored display of high and low intensity.
logical, easy to use, and the results are easy to interpret.
Some of the more important frequency domain
CAUTION
phenomena are:
spectral purity and distortion of
Excessive INTENSITY will damage
oscillators, frequency response, parasitic oscillations,
the CRT storage mesh.
The
and distortion characteristics of amplifiers, frequency
INTENSITY setting for any sweep
parameters of networks and filters, and all types of
speed should just eliminate trace
modulation.
blooming
with
minimum
PERSISTENCE setting.
3-26. The Spectrum Analyzer is capable of analytically
resolving almost any problem whose unknowns are
3-20. Storage. These controls select the storage mode
amplitude and frequency; thus, over and above the
in which the CRT functions. In ERASE, STORE and
general-purpose applications, the instrument is a
WRITING SPEED are disconnected and all written
powerful
observation-and-measurement
tool
for
signals are removed from the CRT. The STORE
surveillance, EMC, and systems work. To define each
selector disconnects the WRITING SPEED and ERASE
instrument application is beyond the scope of this
functions and implements signal retention at reduced
manual.
For further details, there is a complete
intensity. In the STORE mode, PERSISTENCE and
discussion of Spectrum Analyzer applications in
INTENSITY have no function.
Application Note 63A-D. These application notes are
available from the nearest HP Sales and Service Office.
3-21. Writing Speed. In the FAST mode, the rate of
erasing a written display is decreased. Since the
erasing rate is decreased, the entire screen becomes
3-2
