Tektronix 1L30, Instruction Manual

Page: 17 / 129

The LOG position increases the dynamic range of the
display by attenuating large amplitude signals more than
small amplitude signals. This type of display approximates
a logarithm ic response curve and is most effective when
there are large signal amplitude differences.
Operating Instructions— Type 1L30 j?
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3. Adjust the RF CENTER FREQ control a slight amount
to identify the fixed from the tunable signals. The fixed ;
signals should be used, and the tunable markers should I
be tuned so they coincide with the fixed markers to elim­
inate confusion in the display.
■ '*
The LIN (linear) position provides linear signal am pli­
fication, so relative amplitude measurements may be per­
formed over the full 6 cm graticule height.
The SQ LAW (power) position provides a display that is
approximately proportional to the square of the input sig­
nal amplitude. This type display provides an approxim a­
tion of the input signal pow er'and is used to accentuate
small amplitude difference.
In the VIDEO mode, the spectrum display is grounded and
any signal connected to the front-panel VIDEO INPUT con­
nector will be displayed as a conventional (time versus sig­
nal amplitude) display. An uncalibrated G A IN control
provides variable sensitivity adjustment. Maximum sensi­
tivity is approximately 0.1 volt per centimeter.
The impedance of the VIDEO INPUT circuit is approx­
imately 50 ohms; therefore high-impedance probes should
not be used to couple signals to the VIDEO circuit.
Video Filter Operation
The video filter restricts the video bandwidth. This will
reduce zero beats‘ when viewing sigrfals close to minimum
resolution bandwidth. The filter is useful in applications
where the envelope of a pulsed RF spectrum is desired
(Fig. 2-8) or in some cases it may improve the display reso­
lution. See Fig. 2-23. It does, however, restrict the usable
sweep rate because of the filter time constant. The sweep
rate is usually reduced to about 50 ms/cm or slower when
the filter is used.
Dispersion
Dispersion is the swept frequency width, or screen window.
The frequency excursion of the frequency axis of the dis­
play is usually expressed as frequency per centimeter. The
dispersion for the Type 1L30 is adjustable from lO M H z /c m
to 1 kHz/cm in a 1, 2, 5 sequence with an added zero dis­
persion position for fixed frequency operation.
Dispersion accuracy is a function of the IF CENTER FREQ
control position and the DISPERSION RANGE switch set­
ting. See. Characteristics section. Since the IF CENTER FREQ
. control range ± 2 5 M Hz in most the M H z /C M position is
greater than the ± 2 . 5 M Hz range in the kH z/C M position,
the accuracy of the kH z/C M range is improved over the
M H z /C M range.
The front panel DISP CAL adjustment may be adjusted
to recalibrate dispersion for specific IF CENTER FREQ con­
trol settings when a high degree of accuracy is desired
for a particular frequency setting. The procedure is as fol­
lows:
1. Adjust the front panel controls for the desired display.
2. Apply the 1 M Hz CAL MARKERS O UT signal to the
RF INPUT connector. This should provide a picket fence
display. See Fig. 2-9.
4. Calibrate the display by adjusting the DISP-CAL for
the. correct markers per centimeter, or read the dispersion
directly from the marker picket fence.
5. Remove the 1 M Hz markers from the RF INPUT and
reconnect the signal. Perform the desired dispersion meas­
urement.
6. After the measurement, recalibrate the dispersion as
described under the sub-title Front Panel Adjustment.
Resolution and Dispersion
Resolution is the ability of the spectrum analyzer to dis­
play adjacent signal frequencies discretely. The measure
©
2-11
f-. ■
Fig. 2-8. Integrating the display with the video filter.