In order to produce a useful diagram of basestation/antenna coverage it is vital to obtain a scale map/image of the track is helpful, google maps are accurate so you can use this to lift a sattelite image of the racetrack. Once this is done, import it into an advanced paint program or Visio as these will allow you to add transparent circles to represent the Tempest antenna coverage without blocking the detail of the Racetrack underneath. (many paint applications do not understand transparency)
Using tempest, assuming a Antenna/BaseStation coverage radius of 200m you should be able to cover the Audru Ringrada track with 4 base stations and 4 antennas. I have attached a map of the track showing coverage areas from each antenna which will need to be located appropriately. With regards to the map I have tried to ensure the scale is accurate but this is just a basic projection and environmental factors may also have an effect on range.

You will also see that I have indicated the ideal location for the BaseStations. The maximum distance that you can locate your antennas away from the BaseStation is 450 meters, as the antennas will be distributed throughout the track, the BaseStations must be located centrally so we do not fall foul of this limitation.

If the Tempest system is configured in shared mode, 5 users would be able to talk at any one time but allow unlimited number of BeltStations per Antenna/BaseStation. With the tempest roaming enabled this should give them the facility to have multiple referees (5 talking at any one time) and allow them to all move to the scene of an incident without an issue of overcrowding one antenna/BaseStation.