ZSU ARTCC controller reported an unsafe situation relating to frequency blind spot.

Attributes
ACN	1467294
Time
Date	201707
Local Time Of Day	1201-1800
Place
Locale Reference	ZSU.ARTCC
State Reference	PR
Aircraft 1
Make Model Name	Cessna Single Turboprop Undifferentiated or Other Model
Flight Phase	Descent
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	Climb
Route In Use	None
Flight Plan	VFR
Person 1
Function	Enroute
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Time Certified In Pos 1 (yrs) 7
Events
Anomaly	ATC Issue All Types Conflict Airborne Conflict Deviation - Procedural Published Material / Policy

Narrative:

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 as soon as possible 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).

Original NASA ASRS Text

Title: ZSU ARTCC Controller reported an unsafe situation relating to frequency blind spot.

Narrative: 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).

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.