Ok I am fairly mechanical, but getting the existing power antena on my 300SD disengaged from the sheet metal has me puzzled. It has what appears to be a knurled nut underneath that does not see to want to come loose. But I do not know if that is what is supposed to be loosened.

It is probably simple but haven't found any pix or instructions on the forum.

Any help would be appreciated

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83 300SD 280K
78 240D 200K+ sold 10/07
94 BMW 740IL 220K