5-10
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 in 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%. They are readily apparent in the “ZERO
SPAN” view.
Fig.:5-7 Time Domain Signal with
Intermittent Ingress in “ZERO SPAN”
Looking at TDMA signals can be confusing. Implementing return
path modem is necessary to keep current customers and attract new
revenue. Viewing the reverse path in a spectrum graph can give you
a good idea of overall system health. To manage TDMA signals cost-
effectively, you need time domain view. TDMA desired signal
power, undesired noise power and impulse interference could all be
quantified from a “ZERO SPAN” time domain view.