Band 71 Ingress on One Feeder Branch
Complaints of pixelation on channels between 617 and 652 MHz come from eight homes on the same feeder branch of a 550-home node. The node's downstream OFDM channel occupying 618–658 MHz shows MER 40 dB at the node but 29 dB at the affected taps, with errors only when the wind blows. A leakage detector set to the LTE downlink band finds a strong egress signal at 622 MHz near a vacant home's siding, 18 in. from a corroded ground block. The vacant home's drop is still connected at the tap, coiled on the ground, with the house end unterminated. Federal leakage limits are 20 µV/m at 3 m for the relevant band, and your reading is 45 µV/m. The customer in unit 8 asks why their TV is fine when their neighbor's is not.
1. Explain how egress and ingress are related here and why wind changes the errors.
Read the worked answer
Coaxial shielding is reciprocal: a path that lets ingress in also lets egress out. The corroded ground block and unterminated vacant drop act as an antenna. Wind moves the coiled drop and changes the contact of the corrosion, modulating the ingress; that is why errors correlate with wind. The eight homes share the same feeder branch, so the noise is common to that branch and shows up at their taps. Downstream MER at the node is 40 dB because the ingress enters after the node, on the branch; at the affected taps it is 29 dB. The vacant drop is the most suspicious because it is connected, coiled, and open at the house end, which is a classic egress and ingress source.
2. Is 45 µV/m a violation? What immediate actions do you take?
Read the worked answer
45 µV/m at 3 m exceeds the 20 µV/m limit, so treat it as a leakage violation and log it. Immediate actions: disconnect the vacant drop at the tap, terminate the tap port, replace the corroded ground block, and recheck the branch. Then retest with the leakage detector and verify MER at the affected taps. Notify your leakage coordinator per local procedure. Do not just tighten the connector and leave the open drop connected; the open end is the antenna.
3. How do you explain the situation to the customer in unit 8 without blaming the neighbor?
Read the worked answer
Tell unit 8 that the picture is fine because the noise is entering on a neighbor's vacant drop and affects the shared branch unevenly; their outlet may be electrically quieter. Avoid blaming the neighbor. Explain that you found a leak and are fixing it, and that the repair may briefly interrupt service. Give a time estimate and a callback. If the customer asks about safety, explain that the signal is low-level and the concern is service quality and leakage compliance, not a shock hazard.