Radio antenna ground question
 

I have an aftermarket radio installed in place of the basic OEM stock radio. AM reception is crap with the antenna mast on and better with it off but the FM reception is then crap. The resistance is high when I checked the ground side of the antenna wire at the radio. I'm thinking the antenna is not grounded well. How is it grounded? I don't see a ground wire in photos on the web. Does it just ground via the bolt that clamps it to the roof?

As far as I can tell from the schematics, there are 2 wires to the antenna base; the coax (signal & shield) and the pink (12V+ power).

I am guessing the amp circuit grounds via the coax shield.

Hmmm. If that's the case, I wonder if the radio itself has a poor ground. It's currently grounded through the harness wire. I read resistance should test out at less than 2 ohms. Maybe I should see if I can ground the radio case with a jumper wire. There is also a grounding prong projecting from coax adapter cable (need that when installing an after market radio) maybe that's where I'll start. Thanks.

Don, is the signal amp built into the antenna base?

I believe it is. That's why there is a power line coming out of the base. I know a lot of antennas are grounded where they clamp onto the sheet metal. I was wondering if that was my issue. Maybe there is corrosion where it clamps on. I've going off of this https://www.installdr.com/TechDocs/999801.pdf

When you tested the ground, are you sure your other lead was touching a good ground(the "shiny metal" the document references)?

I was touching the ignition lock cylinder. I seemed to ground ok on other tests I did...

That seems to be a good ground on mine also.

Antennas have a "ground plane" not a ground exactly. I am not smart enough to know how antenna amps work. I guess if I cared enough I could GoOgle the subject.

Here is a simple antenna amp. It uses the coax shield for ground.
http://www.net4truthusa.com/jeeprest...dioBooster.jpg