Tektronix 1L30, Instruction Manual

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O p e ra tin g Instructions— Type 1L30
fore be used to measure the pulse width of the pulse mod­
ulated spectrum. This is accomplished with the Type 1L30
as follows:
1. Adjust the DISPERSION control and tune the RF CENTER
FREQ control so the main lobe of the spectrum is displayed in
the center of the graticule, and the side lobes are visible on
each side.
2. Adjust the G A IN control and switch on the necessary
IF ATTEN dB switches, so the main lobe and its side lobes
are within the graticule height.
3. Adjust the scanning rate for optim um spectrum defini­
tion.
4. Adjust the RESOLUTION control so the minima between
lobes are easily discernible without excessive loss of sensi­
tivity. Change the mode selection of the VERTICAL DISPLAY
to accentuate these minima points. (Usually LOG position.)
5. Calculate the frequency width of either the main lobe
or a side lobe as directed under measuring frequency d if­
ference. The pulse,width is equal to the reciprocal o f V2
the main lobe frequency width, on the reciprocal of the
side lobe frequency width. See Fig. 2 -2 ]A.
Repetition Rate: The pulse repetition rate is measured by
switching the dispersion to zero so the analyzer becomes a
fixed tuned receiver. The sweep is then triggered on the sig-
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(A) Pulse width = —
AF
Fig. 2-21. Pulse modulated
mode operation.
2-20
RF display.
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nal and the display becomes a time domain function. The
procedure is as follows:
1. Tune the signal to the display center with the RF CEN­
TER FREQ and the IF CENTER FREQ controls.
2. Change the DISPERSION RANGE switch to kHz posi­
tion, then decrease the DISPERSION to 0. Uncouple the
RESOLUTION control and turn to the fully clockwise posi­
tion. The analyzer is now a fixed frequency device.
3. Set the plug-in oscilloscope Trigger Source selector to
Int position and adjust the triggering controls for a stable
triggered display. The IF CENTER FREQ— FINE control may
require slight adjustment to displace the spectrum null point
from the sweep start. See Fig. 2-12.
4. Set the Tim e/CM switch of the oscilloscope so that sev­
eral pulses of the applied signal are displayed (see Fig. 2-11).
Be sure the Variable Tim e/C M control of the oscilloscope is
in the Calibrated position. The number of pulses displayed is
now a function of the sweep rate and the signal PRF.
5. Measure the number of centimeters between 2 or more
pulses on the graticule.
6. The pulse repetition frequency is the reciprocal of the
measured time between pulses.
The expanded sweep feature of some plug-in oscilloscopes
can be used to analyze or examine small portions of a
spectrum display. In some instances, because of signal drift
or instability, it may be impractical to reduce the dispersion
to make this examination. It is more, practical to tune the
desired portion of the display to screen center and expand
the sweep.
Fig. 2-22 shows an expanded display of a pulsed RF sig­
nal. The null point can be easily examined.
Fig. 2-22. Application of the plug-in oscilloscope magnification
feature. ’
H igh Resolution Capabilities
Figure 2-23 illustrates resolution capabilities of the Type
1L30. The DISPERSION is set to 1 kHz/cm and the RESO­
LUTION is uncoupled and turned fully counterclockwise. To
increase the apparent resolution turn the VIDEO FILTER
switch O N . Resolution is a function of the last IF amplifier
stage of the analyzer; therefore, the illustrations are typical
for any RF frequency with the local oscillator phase locked.