Reverse Path Troubleshooting: Evaluating TDMA Return Path Signals
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5
Fig. 5-6 Signal with High Noise Floor in Zero Span
Intermittent ingress along with the TDMA signal is a pesky problem when
troubleshooting return path issues. This is a hit-or-miss game. With a
spectrum graph you are completely at the mercy of luck. As you can see,
when there is a signal with intermittent ingress (see Fig. 5-7), there are
additional pulses. The “U” marker in this screen clearly shows a peak “D/U”
of 30 dB. The average noise floor is still well over 50 dB down. These
impulses are a mere 10 uSec every 5 mSec. This leaves the probability of
catching these in the spectrum graph less than 0.2%. However, they are
readily apparent in the ZERO SPAN screen.
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