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November 1999 Issue
Reference

Training - Detecting Signal Leakage, Part 4

This month's installment continues a series on detecting signal leakage in the drop system. The material is adapted from a lesson in NCTI's Installer Technician Course. © NCTI.

• Isolating leakage at wall plates, jumpers and CPE
• Repairing signal leakage
• Signal Leakage Sources and Possible Repairs

Isolating leakage at wall plates, jumpers and CPE

Once you verify that the entire outside portion of the drop system has no signal leakage, attention can then shift inside the customer premises. With the leakage isolated to individual outlets, check all possible signal leakage sources inside the customer premises.

Possible signal leakage sources include cable wall plates (Figure 1), coaxial jumpers (Figures 2 and 3) used to configure customer premises equipment (CPE), and in some cases, the CPE itself. Replace any suspect coaxial jumpers. In some instances, poorly shielded CPE may emit RF signals in the critical signal leakage bandwidths.

To isolate CPE-caused signal leakage, remove the coaxial jumper from the RF output on the suspected set-top terminal or videocassette recorder (VCR), then attach a 75-ohm terminator to the RF output port. Monitor the area with a signal leakage detector. If the suspected signal leakage is coming from CPE owned by the customer, follow your system's procedures and policy for informing the customer and making any recommendations for repairs.

Figure 1: Checking out connections at the wall plate

Figure 2: Checking connections at TV set or video cassette recorder

Figure 3: Checking connections at set-top terminal

Repairing signal leakage

Once you isolate the cause of the signal leakage, repair the problem using the logical choice suggested by the leakage source:

1) If the leakage is caused by damaged coaxial cable, replace or repair the cable (as your system policy dictates).

2) If connectors are the problem, tighten or replace the connectors as necessary.

3) If a passive device is causing the leakage, replace the passive device.

4) With active devices, ensure the amplifier housing is providing a good environmental and RF interference (RFI) seal.

5) If CPE provided by the cable system is the cause, replace the device.

6) If customer-owned CPE is the cause, follow your system's policies for informing the customer and removing the device from use.

Following these simple steps will work with single-source leaks. Signal leakage that results from multiple sources may require making several or all of these repairs. The table above outlines signal leakage sources and their possible repair.

Next month's installment will cover recognizing false alarms when trying to isolate the cause of signal leakage in the drop system.

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