I haven't changed out a radio in quite sometime ... however it should have an 'antenna trimmer' adjustment on the unit. This is used for impedance
matching. Check for this and it will most likely solve your reception difficulties. If you call Crutchfield they should be able to assist you with
locating this adjustment screw (potentiometer) and you will find it to be a very quick and simple task.
I could go into what is called in the business as standing wave ratio and antenna reflectivity, but no one really cares. Bottom line is the need to tune your
radio to your antenna and coaxial cable and is called 'trimming' the antenna. Tune to center station and adjust for max volume is basically all there is to it.
Just a taste of electronic wizardry ... a radio does the following: reception, selection, detection, amplification and reproduction.
receives signals ... selects station ... detects intelligence (strips usable data from carrier wave) ... amplifies usable data (turn it up) and reproduces it
or sends it to the speaker.
there you go, it's cosmic man