The black VW is the Peilauto from Agentschap Telecom (although its not uncommon for BNetzA to cross the border to NL or Agentschap go into DE because of EU wide agreements) – it is full of Rohde & Schwarz radio monitoring equipment; a GPS (with a link back to other monitoring kit at Agentschap Telecom HQ in Groningen) and C2000 communications radios.

they used to use VW T4 vans but have gone back to VW Golfs – before that they used VW Passats and had a big yagi antenna (like a tv antenna) hidden in a ski box on the top – might work for BNetzA but few people go skiing in the Netherlands 🙂 TBH I think that R&S sell the kit (about €100 000) and the car/van is given away free – its the most basic model without any central locking (otherwise if there is interference at 433 or 868 MHz the baldy men get be locked out 😛 ).