However, because
o the difficulty producing narrow bandwidth filter with adjustable mid-band frequency, the problem is
avoided "heterodyning". achieve this, multiplier used which outputs the sum and the difference the frequencies applied the
two inputs, resulting from the trigonometric relation:
cos(a)cos(b) (1/2)[cos(a+b) cos(a-b)].SPECTRUM ANALYSER
Connected PC
Spectrum Analyser
Spectrum analysis can used measure the band, detect disturbance lines, quantify phase
jitter direct reading, check the steps, determine the rated frequency, search for residual lines
for comparison, etc. better frequency resolution), more time will necessary with narrow filter than with a
wider filter.
Width the analytical filter
POWER aen>)
) f
C -
\
0Wft3liHz}
J *
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F?Fl
umlmx-
.
With this technique, the bandwidth filter has fixed id-band frequency and the signal analysed is
modified modulation, that the different frequency components are successively modulated the frequency
F0.
Heterodyne spectrum analyser
Spectrum analysis involves moving narrow bandwidth filter front the signal analysed.
Block diagram heterodyne spectrum analyser
The analytical filter
The analytical filter also called the resolution filter. The narrowness the
filter limits the amount data that can supply per second, which means that, obtain large number of
measurement points (i.e. The narrower the filter, the finer the analysis and the closer you
get the shape the line analysed (because the filter itself resembles line). Using different reasoning, could
also said that signal passing through extremely narrow filter can only come out pure sine wave,
represented line!
It tempting use narrower filter analyse signal, but compromises need made
