Wavetek 147 Spécifications télécharger pdf (Page 357)

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Application Notes: Return Path Troubleshooting

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Return Path Egress/Ingress Testing

The FCC states that the maximum allowable limit for egress from dc up to 54

MHz is 15 µV/m at 30 meters.

By utilizing forward path egress techniques, it may be possible to

characterize the return path ingress points to some extent. Testing

stringently at 5-10 uV/m everywhere, including the drops, is probably a

better indication of return path integrity.

Forward path leakage does not necessarily equal ingress, however. Some

sources of leakage and ingress are frequency selective. This would lead us

to believe that a reverse frequency would be better to monitor.

The problem with this is that signals on the return path are only present

when communication is taking place. They are usually very low in level and

bursty in nature.

We can’t insert a reverse frequency carrier at the headend because the

diplex filters would block the carrier.

We can’t insert a carrier at the EOL and look for egress, because sources of

ingress inhibit accurate measurements, but most importantly, the antenna

would be huge; ~23.4’ for 20 MHz!

Using a Variable Dwell Time to Catch Impulse Noise

One problem with a longer dwell time on a spectrum analyzer is that it takes

longer to scan.

If the scan time is too fast, it may skip over fast impulse noise.

The nice thing about a longer dwell time is that it’s easier to catch

intermittent signals because it displays the carrier peak. This is similar to a

peak hold every scan, which makes it great for troubleshooting impulse

noise.

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