C172 Flight Instructor reported ATC radio coverage below 3;000 ft. in the vicinity of BAZ airport is poor and often results in traffic separation issues.

Narrative

Radio coverage and range of San Antonio approach is very poor on most all of their multiple frequencies. This presents a special problem at New Braunfels airport (BAZ) when doing practice or actual instrument approaches. Approach radio coverage is pretty much unusable below 3000 ft. on the east side of the airport and spotty in most all areas surrounding the airport. Everyone including Approach is well aware of this and they are forced to hand off inbound traffic to New Braunfels Tower way too early and Tower; being non-radar; is blind to that traffic until acquiring them visually. Often; after the handoff; Approach has to call Tower on the phone to have them warn the handed-off aircraft of a potential conflict. I personally have had several uncomfortable close-encounters with traffic while doing practice instrument approaches at BAZ which could have been avoided if I could have remained in contact with Approach longer. Its a bit odd that radar and VOR coverage there goes down to 500 ft. or so yet comm radio coverage is pretty much unusable below 3000 ft. If improvements cannot easily be made at SAT; then there needs to be an RCO for the approach freq at BAZ. SAT Approach coverage is poor in most all other directions too. I have been flying 20 miles south of SAT before on a clear day and could actually see the airport visually but yet Approach radio coverage was very poor below 2500 ft.