Sample loop on tower 4
These sample loops were installed to replace the original shielded loops when the FCC mandated improved sample systems in the mid-1970s. A sample loop picks up a small sample of the signal from the tower and feeds it back to the antenna monitor, which displays the magnitude and phase of the tower's contribution to the directional pattern. The loop is a single-turn rigid loop aligned with the center of the tower. The loop is insulated from the tower and operates at ground potential. The feedline is 1/4 inch semi-rigid coaxial cable with a solid outer conductor, in keeping with FCC specifications. I installed the new loops on these towers and fabricated the PVC standoffs for the sample lines during my tenure as chief engineer. I'm suitably impressed that they have withstood the ravages of time and remained firmly in place after more than 40 years. The FM feedline can be seen running up the tower on the left.