Narrative:

Aircraft X wanted flight following and initially contacted me around vdi at 024 feet going southbound. Shortly after calling radar contact the aircraft had VFR traffic at 024 his same altitude off his right side that I was not talking to and targets were merging. I called traffic and ultimately advised aircraft X to descend immediately. The conflict was resolved.aircraft X asked me later if I knew why he wasn't seeing the other aircraft on his ads-B display in his cockpit and I was. Normally he says he sees other aircraft that have a transponder because they are relayed from radar sites to the ads-B antennas and then relayed to his aircraft. He was in a known ads-B coverage area as published by the FAA. I took his phone number down and told him I would try to find an answer. I talked to our tech people and they weren't aware of any ads-B outages or radar outages at the time.the pilot said this happened one other time near sav airport.educate controllers and pilots about limitations of ads-B and coverage limitations.

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Original NASA ASRS Text

Title: ZJX Controller reported a VFR aircraft conflict which was resolved; but the pilot of one aircraft wondered why they were not seeing aircraft on their ADS-B.

Narrative: Aircraft X wanted flight following and initially contacted me around VDI at 024 feet going southbound. Shortly after calling radar contact the aircraft had VFR traffic at 024 his same altitude off his right side that I was not talking to and targets were merging. I called traffic and ultimately advised Aircraft X to descend immediately. The conflict was resolved.Aircraft X asked me later if I knew why he wasn't seeing the other aircraft on his ADS-B display in his cockpit and I was. Normally he says he sees other aircraft that have a transponder because they are relayed from radar sites to the ADS-B antennas and then relayed to his aircraft. He was in a known ADS-B coverage area as published by the FAA. I took his phone number down and told him I would try to find an answer. I talked to our tech people and they weren't aware of any ADS-B outages or radar outages at the time.The pilot said this happened one other time near SAV airport.Educate controllers and pilots about limitations of ADS-B and coverage limitations.

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.