Tektronix 1L40, Инструкция по эксплуатации

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Operating Instructions— Type 1L40
A. N arrow pulse w id th produces w ide spectrum lobes. Low pulse re petition frequency produces low re p e titio n rate line density.
B. W ide pulse w id th produces n a rrow spectrum lobes.
C. High pulse re p e titio n frequency produces hig h line density.
Fig. 2 -1 7 . Pulse w id th and PDF effects on pulse m odulated spectrum.
where tj> (pulse width) is measured in seconds and band­
width is the selected resolution bandwidth of the analyzer
in hertz. Spectrum analyzer sensitivity measurements should
therefore be made only with a CW signal applied, as indi­
cated in the Performance and Calibration checks.
Signal Identification and Frequency
Measurement
Spectrum Analyzers that have no preselection prior to
the first mixer w ill display signals which do not conform
to the indicated frequency reading of the dial, these
signals are referred as spurii (many or plural) or spur
(singular) which are colloquial terms used to relate to
spurious responses. (See definitions fo r spectrum analyzer
terms). They are the products of the following:
1. IF feedthrough: In the Type 1L40, the IF passband
is 150 to 250 MHz. Frequencies within this passband may
appear as non-tunable or IF feedthrough signals on a 100
MHz dispersion screen.
2. Signal images: The dial scales of the Type 1L40 Spec­
trum Analyzer are calibrated below the frequency of the
tunable first local oscillator. The response to an input
signal whose frequency is above the local oscillator
frequency by a difference of the IF, is called an image
response. The input signal that is the IF below the oscillator
frequency is the true response. For example: the analyzer
w ill receive a 2.7 GHz signal at a dial reading of 2.7 GHz
(oscillator frequency of 2.9 GHz) and at a dial reading of 2.3
GHz (oscilloscope frequency of 2.5 GHz). At the image re­
sponse point, the local oscillator frequency is 200 MHz (IF)
below the input frequency instead of 200 MHz above the
input frequency. Note that the difference between these two
response points is 400 MHz or twice the IF.
The dial is calibrated for signal frequencies that w ill mix
with harmonics (2nd through the 10th) of the local oscillator.
3. Higher order modulation (harmonic conversion and
inter-modulation)— signals: Any of the products (sums and
differences) of the frequency multiples from the local oscilla­
tor and the signal, plus the myriad of combinations of more
than one input signal that produce a frequency within the
IF passband. The combination of the 2nd harmonic of an
input signal mixing with the fundamental of another input
signal to produce the IF (3rd order) is the most severe.
The possible combinations can be expressed mathemati­
cally as; nfsig ± mf|0 = IF; where n and m are intergers
including 0 and indicate the harmonic order of the signal
or local oscillator frequency. For example: A local oscilla­
tor (dial calibrated) frequency of 2.0 GHz could mix with
frequencies of 2.2 GHz, 1.8 GHz, 2.2 GHz, 3.8 GHz, 6.2 GHz,
5.8 GHz, etc., to produce a 200 MHz IF.
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