I have a PC FM radio peripheral. It has a standard telescopic steel
aerial that plugs into a base. This works quite well.

However, I would like to recieve some signals that are too weak for
this arangement. I have an external TV yagi, but attaching it either
reduces the recieved signal or increases it only slightly.

Could impedence differences be an issue here? If so, what is the likely
impedence of the yagi and the peripheral?