A regular paper clip can work as the pin in a female SMA connector.
The wire for the paper clip is just the right diameter.

Stefano wrote:
> Thanks everyone.
>
> In the end I solved the problem with two unused SMA connectors I
> happened to find at the lab I work, to manufacture a cable to
> reposition the antenna.
> The only problem was the cable, cause I could not "borrow" a 2.4Ghz
> cable as well.
> So I simply tried with a coax BNC cable (the ones used for
> oscilloscopes, if you used one). Soldering was a mess, especially cause
> I had to invert the SMA central pin from male to female.
>
> Being in an already good spot, I kept the cable very short. It's maybe
> less than 2ft now. As soon as I connected it the signal was better, but
> it will go down to nothing from time to time in an unrealiable way. So
> my last guess before throwing everything away was to put some aluminum
> foil around soldered spots at the cable ends, and that surprisingly
> worked wery well. Now I consistently get a "very good" signal.
> I may add a cantenna or parabola on either the AP or th receiver to
> reach "excellent".
>
> Thanks for all suggestions.
>
> Stefano