May 1974 | NTIA Technical Memo OT TM 74 164

Propagation assessment for FACSFAC links San Clemente Is./Pt. Lorna and North Is./ Imperial Beach

H. T. Dougherty

Abstract: This report reviews the available documentation for two links of the FACSFAC microwave system and the findings of on-site inspections. It is recommended that the present maintenance program be supplemented by additional performance monitoring. This should include periodic calibration of received signal levels and the periodic measurement of the combiner performance, receiver-quieting, and idle-channel noise. At present, one microwave link does not appear to have sufficient clearance for high-reliability performance. Repositioning the lower terminal to a higher elevation will remedy this situation. A second microwave link does not have sufficient frequency diversity spacing, at present, to offset deep fading due to sea-surface reflection. The frequency diversity separation should be increased or replaced by space diversity. However, this should not preceed a complete check-out and refurbishing of antennas at both terminals. Path obstruction does not appear to be the major cause of outages, with the possible temporary exception of super-structure traversing the path when a ship moves into or out of Marginal-Wharf Berth L. If this latter case occurs often enough to become a problem in the future or if implementing improved diversity is not feasible, then use of an offpath passive reflector (to replace the present path) should be explored further. Proper positioning of a bill­board passive reflector could prove a most effective remedy for the multipath due to sea-reflections.

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