Poor radio reception

I have a 2006 Tacoma Prerunner which I got used 2 yrs ago. The radio has always had lousy reception with a lot of static. I'm currently installing a new double din head unit with HD radio and once again, it has poor reception.
I tried plugging in a cheap antenna dirrectly into the new radio holding the antenna in my hand and the reception was fine.

My question is, does anyone know how to test the individual parts of the antenna system to find out where the issue is without buying all of the parts
(antenna base, mast, antenna wire etc)?

 

The issue is corrosion in the factory antenna base. It has been well documented.

 

I'll try changing that out. Thanks for the help.