Manual SPECTRAN V5
© Aaronia AG 2016 | www.aaronia.com
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CORRECT MEASUREMENT
5.2. Harmonics
A typical effect when working with spectrum analyzers:
When dealing with comparatively strong signals, a number
of weaker signals with fixed offsets relative to the actual sig
-
nal appear, the so-called „harmonics“. These are “phantom”
signals with frequencies that are multiples of actual signals.
For example, a 400MHz signal will also be visible around
800MHz, 1200MHz, 1600MHz etc., a 1800MHz signal will
also appear at 3600MHz, 5400MHz and so forth. These are
commonly called second harmonic, third harmonic etc.
Thus; when in doubt, one should always consider an addi-
tional measurement at half the center frequency. If a cor-
respondingly stronger signal is found there, the previously
measured one would be a harmonic.
With the current firmware, Spectran already attenuates har
-
monics by approximately 30-50dB, depending on signal
strength.
5.3. Sensitivity
Please note that the noise floor (and therefore sensitivity)
in spectrum analyzers can be subject to significant variation
depending on frequency.
Even a frequency adjustment of just a few MHz can deci
-
sively alter the noise floor characteristics. In general, howev
-
er, Spectran’s noise floor increases with lower frequencies,
while sensitivity decreases.
A practical example: Using the same filter settings, you can
measure considerably weaker signals at 5 GHz than at, say
100MHz.
