Tektronix 1L20, Инструкция по эксплуатации

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O perating Instructions— Type 1L20
NOTE
For maximum accuracy, the two signals being com­
pared should be referenced to the same place on
the screen by changing the RF CENTER FREQ con­
trol only, since the IF bandpass response is not
absolutely fla t, but can vary as much as ± 1 . 5 dB.
The IF CENTER FREQ, DISPERSION-COUPLED RES­
OLUTION, FINE FREQ, and sweep speed controls
should not be moved while comparing the two
signals.
Absolute Frequency Measurements
Absolute frequency measurements can be made from the
RF CENTER FREQ dial with an accuracy of ± 2 MHz + 1 %
o f the dial reading. To measure the frequency of an applied
signal, proceed as follows:
1. Check the setting of the IF CENTER FREQ CAL adjust­
ment and HORIZONTAL POSITION controls as directed
on page 2-3.
2. Set both IF CENTER FREQ controls and the FINE FREQ
control to midrange (000).
Fig. 2-7 . Frequency difference measurement between two signals.
DISPERSION RANGE setting = MHz
DISPERSION setting = 2
Frequency Spectra Measurements of Pulsed
Signals
3. Set the DISPERSION RANGE switch to kHz/CM.
4. Set the DISPERSION switch to 500.
5. Move the signal being measured to the exact center of
the graticule using the RF CENTER FREQ CONTROL.
6. Read the frequency indicated by the RF CENTER FREQ
dial. For example, with a dial reading of 100 MHz, the
actual signal frequency is 100 MHz ± 3 MHz (i.e., 2 MHz
+ 1% of 100 MHz = 3 MHz). For a dial reading of 1000
MHz, the actual signal frequency is 1000 MHz ± 12 MHz.
(i.e., 2 MHz + 1% of 1000 MHz = 12 MHz.)
Frequency Difference Measurements
Frequency separation measurements can be made between
signals that are up to 100 MHz apart. The measurement is
made as follows:
1. W ith the two signals displayed on the screen, set the
DISPERSION RANGE and DISPERSION switches so that the
signals are spaced as far apart on the screen as possible.
(Center the two signals on the screen each time the DISPER­
SION switch is set to a lower position.)
2. Set the sweep rate of the oscilloscope and the RESOLU­
TION control o f the Type 1L20 for the best defined signal
peaks.
3. Measure the distance in graticule divisions between the
two signals (see Fig. 2-7). 4 5
4. M ultiply the distance measured in step 3 by the DIS-
PERSION/CM setting to determine the frequency separation.
For the example of Fig. 2-7,
fs = (7 cm) (2 MHz/cm) = 14 MHz
5. Accuracy of the measurement will vary according to
the DISPERSION and DISPERSION RANGE settings. See
Table 1-2.
The main frequency lobe and side lobes of a pulse- modu­
lated signal can be displayed and used to measure the
pulse width as follows:
1. Adjust the DISPERSION— COUPLED RESOLUTION con­
trol and the RF CENTER FREQ Control so that the main fre­
quency lobe o f the displayed signal is in the approximate
center of the graticule and the side lobes of interest are
visible. (See Fig. 2-8.)
Fig. 2 -8 . Spectrum for a square RF pulse.
2. Set the G AIN control and the IF ATTEN switches so
that the main lobe fills the screen vertically and the side
lobes are of sufficient amplitude for viewing.
3. Set the sweep rate of the oscilloscope so the spectrum
is well defined (Sweep Rate = 1 /50 pulse repetition rate).
4. Set the RESOLUTION control so that the low points in
the spectrum are easily discernible without excessive loss of
sensitivity. (Changing the VERTICAL DISPLAY Mode— LOG,
LIN, or SQ LAW— may make these points easier to see.)
2-8