Tektronix 1L40, Инструкция по эксплуатации

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Operating Instructions— Type 1L40
Frequency Measurements
Frequency measurements taken from the RF CENTER FREQ
dial are accurate to within
±
(2 MHz - f 1 % of the dial
reading). The frequency of an applied signal is measured
as follows:
1. Check the calibration of the IF CENTER FREQ CAL
adjustment as described previously.
2. Set both the IF CENTER FREQ controls and the FINE
RF CENTER FREQ control to their midrange (000) position.
3. Set the DISPERSION RANGE switch to kHz/CM and
the DISPERSION selector to 500 kHz/cm positions.
4. Tune the RF CENTER FREQ control to center the desired
signal within the graticule area.
5. Read the frequency indicated on the RF CENTER FREQ
dial. This reading is accurate to within ± (2 MHz + 1%
of the dial reading). For example: A dial reading of 5.0
GHz indicates the signal is 5.0 GHz dfc (2 MHz + 5 0 MHz)
or, between 4.948 GHz and 5.052 GHz.
Accurate frequency measurements can be performed by
applying a calibrated or crystal-controlled frequency to
the RF INPUT and calibrating the dial near the frequency
range of the input signal; then tune the input signal to the
same screen position and note the dial reading plus or
minus the measured dial error.
Frequency Difference Measurements
Frequency separation measurements to 100 MHz can be
performed as follows:
1. Adjust the DISPERSION RANGE switch and the DISPER­
SION selector so the signals to be measured are the maxi­
mum number or graticule divisions apart on the display.
2. Set the Time/Cm selector and the RESOLUTION control
for optimum signal definition.
3. Measure the distance in centimeters between the two
signals (see Fig. 2-19).
4. M ultiply the measured distance in step 3 by the
Dispersion/Cm setting. This is the frequency separation or
frequency difference between the two signals.
NOTE
Accuracy o f this measurement depends on the DIS­
PERSION
RANGE settings. See Characteristics
section.
Frequency Stability
The Type 1L40 may be used to measure both long and
short term frequency instabilities, when the local oscillator
is phase locked to a stable crystal-controlled reference fre­
quency. See Stability in Characteristics section.
Short term stability measurements apply to fast frequency
changes such as those caused by power supply noise and
ripple, vibration or other random factors. Fig. 2-20 shows
the random frequency modulation of a klystron. * 1
----- 1
1
I I L I i n
_1_ W
— —
S S I
Fig. 2 -2 0 . Short term s ta b ility measurement. Random FM character­
istic o f a klystron.
DISPERSION is 2 kH z/cm and RESOLUTION is
1 kHz. O scillator FM is ab out 6 kHz.
7 cm or 14 MHz
mJ
1
1
Fig. 2 -1 9 . Frequency difference measurement between tw o signals.
DISPERSION RANGE setting = M H z/cm
DISPERSION setting = 2
Frequency difference — 17 cm) 12 M H z/cm ) :— 14 MHz
Long term stability measurements require a recorder, a
series of photographs, or the use of a storage oscilloscope
to show frequency d rift as a function of time. Temperature
compensation can be computed by this process.
Amplitude Modulation
Modulating frequency or frequencies and modulation
percentage are the quantities most often desired from an
AM signal measurement. Fig. 2-14 illustrates some amplitude
modulated signals, the methods to measure the modulating
frequency, and modulation percentage.
Over-modulation produces extraneous sidebands result­
ing in a spectrum that is very similar to the spectrum of a
multi-frequency modulated carrier. Over-modulations are usu­
ally distinguished from the multi-frequency modulated dis­
play because the spacing between sidebands is equal,
while the sidebands in a multi-frequency spectrum w ill be
arbitary unless the modulating frequencies are harmoni-
2-19