Have been to a taxi firm in Gainsborough today to look at their radio system which had stopped working.
The firm had reported that the car could not talk to the base and vice versa. I Found numerous faults including an open circuit magmount aerial system on the car, which was the cause of the car not being able to talk to the base radio.
The base station was also not transmitting, even if the car was parked almost next to the base station aerial system. Even with the car aerial centre wire detached at the aerial end, you should have received a signal, as my frequency meter was reading that the base transmitter was transmitting a frequency.
The base station transmission could also be heard on my handheld scanner held near the radio. What it turned out to be was the base station power supply, which was a cheap CB type one. A few weeks previously the owners had decided to put the base radio in one of the cars for some reason. This was doing what they wanted, but they had also used one of the mobile radios as the new base station.
The original base station was set to 5W RF output which the cheap power supply could cope with. The mobiles however are set to a the higher legal output that they can use. Hence the cheap power supply was under strain, and had partially failed, i.e, the radio lit up, but could not cope with the current being drawn by the higher powered taxi radio transceiver.