Variable Persistence and Storage Functions

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