Over time your car radio may start having reception problems and you'll need to determine the cause. Radio signals picked up by the antenna mast travel through an antenna cable to the radio. You will not receive a clear AM or FM signal for some or all stations on the radio if there is interference anywhere from the antenna mast to the radio. You can easily determine if there's an interference by using an ohmmeter.
Connect one of the leads on the ohmmeter or multimeter (the multimeter can act as an ohmmeter) to the antenna mast on the vehicle. You can do this directly or by connecting a wire from the antenna to the ohmmeter.
Locate the cable from the antenna that is plugged into the back of the vehicle's radio. Unplug the cable from the radio.
Insert the centre pin of the antenna cable into the other lead on the ohmmeter.
View the display on the ohmmeter. It should read between zero and two ohms if your antenna connection is working properly.