Sencore-tech-tips-216-understanding-and-using-on-channel-tests-cn-and HUM – Manual (PDF)

Erik from ManualsPlus — Fri, 26 Dec 2025 11:31:54 +0000

The manual provides guidance on setting up, operating, and troubleshooting on-channel tests for carrier to noise ratio (C/N) and HUM in CATV systems, emphasizing the importance of these measurements in maintaining signal quality. It explains how poor C/N and HUM can degrade picture quality, details potential sources of interference, and offers strategies for identifying and resolving these issues before they impact customers.

Brand: Sencore-tech-tips-216-understanding-and-using-on-channel-tests-cn-and
Model: HUM
Type: manual
File size: 255.2 KB

Manual Overview

The Sencore Tech Tips manual #216 provides guidance on understanding and using on-channel tests for Carrier to Noise (C/N) ratio and HUM in CATV systems. These tests are crucial for maintaining signal quality and diagnosing issues that affect picture delivery to customers. Poor C/N performance results in visible “snow” on the screen, with a threshold of approximately 39 dB C/N. Noise originates at the headend and amplifies through the system, often exacerbated by components like splitters and cables. HUM, on the other hand, is low-frequency AM distortion, often caused by power supply issues or corroded connections. It manifests as vertical bars rolling through the picture. Troubleshooting involves isolating the source of HUM, which can be identified using the SL750’s VOM for AC and DC power supplies. Regular measurements of C/N and HUM are recommended to preemptively address issues before they become visible to customers. Calibration and adjustments involve using correction factors for bandwidth and shape, ensuring accurate measurements. The manual emphasizes the importance of these tests as part of routine maintenance to comply with FCC regulations and deliver optimal signal quality.