Car Radio Trimmer Capacitor:

To obtain maximum performance of your radio, you will need to provide a good quality antenna to your car radio. You also need to be sure that the connection plug is clean and free of rust and oxidation before you plug it into the car radio jack.

Also, there is usually an adjustment that you could make that may marginally improve your radio reception. Most car radios have a “trimmer” capacitor that enables the user (after the radio is installed in your car) to peak and tune the antenna specifically to the car. 

If applicable to your radio, we may have added a label to your radio pointing out a small hole in the chassis when we work on your car radio.  This is labeled: ANT TRIM.  After the radio is warmed up, tune in a fairly weak station.  Insert a small slotted screwdriver in the hole connecting to a small screw.  Turn the screw about 1 full turn one direction, go back to the start, then, turn the other direction.  You want to tune until you hear the station come in the strongest.  DO NOT TURN more than +/- 1 turn from the initial starting point or the screw may fall out.  When your radio was in for repair, we peaked this for our test antenna.  Our default setting may be adequate ok for you.