Several km range is correct for free line of sight. For urban environment the range is lower you should be able to reach more than 400-500 meter. This will hower depend on number of buildings, reflection etc. How is the board placed in the car? Have you tried to leave the car and measure by walking? It is quite challenging to measure inside a car as all the metal will shield the signals. You should also measure the output power to verify that you actually are transmitting 27 dm. Also verify that the battery is full before testing.
Last Update: October 9, 2017