Tektronix 1L30 Instruction Manual page 18

Operating instructions— Type 1130
Fig. 2-9. 1 MHz Markers Output signal (phase lock reference) ap­
plied to the RF INPUT connector to check dispersion calibration.
of resolution is the frequency separation (in Hz) of two equal
amplitude signals when the notch or dip between these
signals is 3dB down. The resolution for a given display is
a function of sweep speed, dispersion and bandwidth of the
most selective (usually the last IF) amplifier in the signal
path.
Resolution bandwidth is approximately the — 6dB band­
width (with Gaussian response) of the analyzer, with the
dispersion and sweep time adjusted for the minimum dis­
played bandwidth to a C W signal. Resolution and resolu­
tion bandwidth become synonymous at very long sweep
times.
As the analyzer sweep rate is increased, the amplitude of
a C W signal decreases and the bandwidth increases; which
signifies that both the sensitivity and resolution of the an­
alyzer have been degraded by the increased sweep rate.
The loss of the analyzer sensitivity due to sweep rate and
the dispersion can be expressed mathematically as:
where S/Sc is the ratio of the effective sensitivity to the
analyzer measured sensitivity, at very slow sweep times or
with zero dispersion.
D is the dispersion in hertz
B is the —3dB bandwidth of the analyzer in hertz
T is the sweep time in seconds, or —
velocity.
These same variables also determine the resolution of
the analyzer. The loss in resolution can be expressed as
follows:
2-12
W here R/R0 is the ratio of the effective resolution o f the
an alyzer to the analyzer measured resolution ba nd w id th at
very slow sweep speeds.
taken as the displayed w idth o f the C W signal at the . — 6
c!B point.
The best resolution fo r a given dispersion and sweep
time is expressed as:
A nalyzer definitions.
The resolution of the Type 1L30 Spectrum A na lyze r is
optim ized for most settings of 1 he DISPERSION selector when
the RESOLUTION! control is in ihe coupled position.
lution however, can be varied from ap pro xim ately 100 kHz
to less than 1 kHz by uncoupling the RESOLUTION control
and adjusting it as an independent function of the DIS­
PERSION selector.
To adequately resolve pulsed spectrum inform ation, the
resolution
order o f 1/10 of the side lobe frequency w idth or the re­
ciprocal of the pulse w idth.
usually set, after the sweep rate Lias been adjusted, for
optim um main lobe detail.
Selecting the Sweep. Ra»e
The sweep rate fo r w ide resolution coupled settings is
usually set just above the visual flicker setting; however,
is the scanning
as the DISPERSION is decreased the sweep rate w ill begin
to a ffect the 'resolution and sensitivity of the analyzer, as
described unc!er Resolution.
settings are reduced the sweep rate should also be reduced
to m aintain sensitivity and resolution.
W ith the DISPERSION control set io 0, the analyzer func­
tions as a fixed tuned receiver. The analyzer then displays
time dom ain characteristics of the signal m odulation w ith in
R0 is somewhat a rb itra ry and is
Dispersion (in Hz)
Sweep Time (in s)
bandw idth of the analyzer should
The RESOLUTION control is
See Fig. 2-10.
Therefore, as the DISPERSION
See S p e c tru m
Reso­
be on the
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