116 Chapter 15 - Spectrum analyzer
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15.13
Ingress measurement in the return path
This function is activated via the menu item
INGRESS
. Ingress refers to all interference spectra
those mix with the signal in the return path. Those can be strong short wave stations, CB radio,
baby monitors or interference emissions from electrical machines. Badly shielded return path
components and incorrectly mounted plug connections can also increase the ingress. Ingress
reduces the signal-to-noise ratio of return path signals and can therefore lead to errors in
transmission.
The consequence is that the required data rates in interactive cable networks can no longer be
maintained. It is therefore crucial to keep ingress as low as possible.
To support ingress measurement, the instrument provides a special function.
Figure 15-8 Spectrum analyzer - Ingress measurement
The frequency range from 5 to 65 MHz is divided into 4 ranges. Within these ranges, the maximum
level and the frequency with which this level occurred is continuously measured and shown on the
display. The instrument also shows the elapsed time since the start of the ingress measurement.
The spectrum in Figure 15-8 shows a strong interference at 27 MHz (CB radio). You can end the
ingress measurement by selecting the menu item
BACK
. The ingress measurement makes use of
the max hold function.
