36
Chapter 7 - Analyzer Mode
AMA 310/UMS V21.0
Figure 7-7 Graphics and LC display of the analyzer at a reference level of 75 dBµV
The attenuation selected automatically by the measuring instrument can be manipulated by the
menu item
ATTEN.
in 5-dB steps.
-5dB
reduces the input attenuation of the instrument,
+5dB
increases it.
Figure 7-8 Attenuation menu in analyzer mode
A higher attenuation than the one automatically selected is required if levels are to be measured
which are significantly higher than the reference level (higher large-signal immunity of the RF
input!).
A lower attenuation can be set if small ingress portions and/or the noise floor among the useful
signals have to be evaluated more exactly.
Care should be taken if the attenuation is reduced. Thus, the RF input may be easily overloaded by
the useful signals applied. The result of an overload are distortions, which become noticeable by
harmonics and mixing products from the useful signals. This means signal portions arise which are
not contained in the measured signal, but are produced by the measuring instrument itself.
Particularly disturbing is this effect with narrow-band signals (high signal level within a small
bandwidth), a maximum results when sinusoidal carriers are measured, as is proven by the
following figures. Based on Figure 7-7 (ideal attenuation (15 dB) and measuring electronics
optimally driven) the attenuation is reduced step by step by 5 dB. Due to the very good properties
of the receiver, still no negative effect is visible at attenuations of 10 dB and 5 dB, actually more
detailed information on the signal portions "below" the sinusoidal carrier can be gathered. However,
at 0 dB attenuation the overloading of the instrument is immediately visible.