Cessna Single Turboprop Undifferentiated or Other Model
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 7
Communication Breakdown; Time Pressure
ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy
ATC Equipment / Nav Facility / Buildings
Aircraft X was at FL110 with assigned altitude to cross GABAR intersection at FL060. When the aircraft was east of DANDE intersection; I noticed a VFR aircraft climbing opposite direction out of FL075. I attempted to communicate with Aircraft X several times for a traffic alert because the aircraft was in a frequency blind spot. I was able to relay the traffic information and a vector through company aircraft in the vicinity; to avoid a possible conflict. Closest proximity 4.7 NM and 700 feet. Area between DANDE and GABAR is a common area of frequency range problems.The frequencies must be fixed ASAP to improve coverage. The process for getting them fixed is unacceptable and the added workload that is required to keep the unthinkable from happening is a distraction and threat to the safety of the National Airspace System (NAS).
ZSU ARTCC Controller reported an unsafe situation relating to frequency blind spot.