With the DISPERSION control set to 0, the analyzer func-
tions as a fixed tuned receiver. The analyzer therefore dis-
plays time domain characteristics of the signal modulation
within the bandwidth capabilities of the analyzer.
Timing information such as pulse repetition rate may be
obtained by triggering the sweep on the INT signal source
and switching the TIME/DIV control to a calibrated sweep
rate that will permit measurement in time between the modu-
lation pulses. See Fig. 2-13.
Triggering the Sweep
For most applications the trigger LEVEL control is switched
to the FREE RUN position and the sweep repetition rate is
a function of the TIME/DIV selector settings.
In some applications, particularly at 0 dispersion, or when
slaving the Type 491 to a recorder, it may be desirable or
necessary to trigger the display. The Type 491 may be trig-
gered from the following three sources: INT, LINE and EXT.
When the SOURCE switch is in the INT position, the dis-
play is triggered on the video display. The Type 491 re-
quires approximately 0.2 division of signal amplitude for
internal triggering. If the sweep will not trigger on INT when
Fig. 2-12. VERTICAL DISPLAY Modes showing a 100 MHz carrier
the LEVEL control is adjusted, it may be necessary to tune
signal modulated by 20 kHz.
2-13
