Antenna Mast Threads/Stud Too Short?

Just picked up our 2005 Prius and as mentioned in another thread have poor FM radio reception. I've gotten a couple very helpful replies to my overall problem, with a number of things on my list of things to check out...

I'm starting with the easiest issue, the antenna mast. I noticed that the stud is about 1/8" of an inch shorter than the center hole/threads in the base, so that even when fully right, the tip of the antenna mast stud will not make contact with the base of the center hole.

Only the threads make contact, and the small bit of metal around the top of the threads where it makes contact with the small bit of metal around the base of the mast stud threads.

Is that right? Is thread contact all that is needed for good reception?

I would have thought the stud and the center hole threads would be the same length.

If this is a possible culprit, I was thinking of putting some copper in there (maybe a bit of heavy guage wire, or cut an old penny), so the base of the stud would press into the copper which would press into the base of the center hole.

Thoughts?

 

thanks for the info, i guess i'll have to dig deeper into the audio system/antenna wiring...