I know nothing about this, but after reading your post this is what came to my mind.
On the back of both my SDA and MDA there is a rubber "cork" that has some sort of connector behind it. It isn't mentioned in the user guide, so I don't know for certain...but it looks to me like it might be a place where an external antenna connects. It looks like it receives a small push pin connector (coaxial) like I saw as an add-on antenna on a router one time...very small.
I've attached one very blurry image. Sorry I can't do better.
Click to view attachmentBefore posting, I just did a Google search for "SDA external antenna" and confirmed it is an antenna port.
See this eBay listing for a picture of it on the MDA.