Solar sunroof messing with mobile and GPS?

[sssam]

Ever since getting my 97 D2 I've struggled with getting decent phone reception and get almost no satnav gps reception. I put it down to a kind of 'Faraday's cage' type effect of that enormous spool of wire in the roof which is the solar sunroof. Given the solar panel doesn't appear to do anything anyhow is it possible to replace this with normal glass? Was there a straight glass version of the sunroof made? Has anyone else had similar problems?