Ed Murlatt & Associates, Inc.
RF Services for the Broadcast Industry
When Bad Things Happen to Good Coax
Preventive maintenance can help reduce damage to passive RF systems resulting from anchor connector (bullet) failure. Rigid coax transmission line has connections at roughly 20' intervals. The bullet that connects the inner conductors can fail over time due to wear caused by thermal expansion and contraction. The length of time it takes for failure varies widely with the bullet design, length of the line, ambient conditions (both delta temperature and wind conditions), percentage of power handling capacity applied, hanger condition, presence of moisture inside the line, and other factors. Broadband time domain analysis of the line can help find failing connections before there is a total burnout, greatly reducing off air time and repair cost.
The photo below (left) shows a failed anchor connector. We were asked to sweep this transmission line as part of the due diligence inspection being conducted prior to purchase of the station. Repairs involved replacing one section of inner conductor and cleaning the section above and below the burn. We provided technical assistance during repairs then measured the line after the repair. The two plots below show the broadband time domain response before (center) and after (right) repairs with marker 2 indicating the failure point in the center plot and marker 4 showing the same point in the plot on the right. Had this not been caught, the failure would have looked more like the photos at the bottom of this page! Click on any of the tumbnails to open a full size picture in a new window, then click to zoom.
Below are what total burnouts look like. The shots are from various sites. In all cases, several sections of line required new inner conductors, bullets, and/or teflon insulators, and hundreds or feet of line had to be cleaned. In a couple of cases some outer conductors needed to be replaced as well. Needless to say the repairs were quite costly, and some took several days.