Chapter 7 - Analyzer Mode
35
AMA 310/UMS V21.0
Figure 7-6 Graphics display of the spectrum with activated MAX-HOLD function
7.6
Reference Line
In all figures above a horizontal dotted line in red lettering "ref" can be seen. This is the level
reference preset in the UMS settings (see Chapter 8.1.3 - Network Settings) which should
correspond to the nominal input level of the CMTS. The scaling of the level axis is done
automatically depending on the reference level set!
7.7
Input Attenuation
In order to drive the sensitive RF input stages and the analog-to-digital-converter (ADC) of the
instrument in an optimum way and/or not to overload it, the RF input signal of the AMA 310/UMS
has to be attenuated depending on the expected level conditions at the RF input. The instrument
derives the "level conditions to be expected" from the reference level set.
The automatically selected attenuation is shown on the bottom left in the LC display.
As shown for example in Figure 7-3 and Figure 7-4 no RF attenuation is required for a reference
level of 60 dBµV, the display in the LCD therefore reads "Att=00dB".
If for example a value of 75 dBµV is predefined as reference level in the UMS settings (see
Chapter 8.1.3 - Network Settings), the display reads "Att=15dB". This means that the input signal is
attenuated by 15 dB before it is passed on to further signal processing.
The following figure shows the graphics and LC display for exactly this case (Ref = 75 dBµV, Att =
15 dB). Four sinusoidal carriers at about reference level are measured: