Here is my version of that repair
* remove the right hand front window column plastic cover
(http://lh5.googleusercontent.com/-PE6abX61Z0k/Ub2ZQFpTzTI/AAAAAAAAMqM/gRlfvIO9IhU/s1000/antena1.jpg)
!! Here is the place to mention that if your car have interior light over the rear inside mirror the taking it out i presume will skip the idea of the follow procedure, but mine car haven`t it that`s why i continue:
* take off the sun shades hinge via 2 torx 20 bolts remove , and their other holders. In my car that was one screw, in some models can be 2
* once make that, the roof cover front part fell down and make enough space to work in. Take small ratchet with 8mm(short one) tip and small pin/or tiny screwdriver
Last ones are needed to take that metal cap out:
(http://picasaweb.google.com/kovachev.svetoslav/CitroenXantia#5890032411976576050)
(http://lh3.googleusercontent.com/-fFzlj3UMB4M/Ub2ZQ8hKNII/AAAAAAAAMqM/QMEzhhExT_U/s1000/antena2.jpg)
* under is the nut :
(http://lh6.googleusercontent.com/-xf6smMplfW0/Ub2ZSWbjZYI/AAAAAAAAMqM/QQmbAxTLCsE/s1000/antena4.jpg)
(http://lh4.googleusercontent.com/-AfWiboaanPc/Ub2ZTqmwCAI/AAAAAAAAMqM/W4-8c7fCKo8/s1000/antena6.jpg)
* and just take it out - PLEASE, be sure that you have the right shape base mount antenna!!
(http://lh5.googleusercontent.com/-YF2KqvsQryw/Ub2ZTck2zaI/AAAAAAAAMqM/6FYhspAZ0Fs/s800/antena5.jpg)
Тоест аналогична форма и размер на поставката и пин предотвратяващ завъртане.
If you decide to change the cable also, cut close to that metal end the original one, attach to it the new one on it`s radio plug and plug it to the radio follow the route of the original one.
Old:
(http://lh6.googleusercontent.com/-RnZ2rJmr_z8/Ub2ZVdmPhsI/AAAAAAAAMqM/shSJU8MMVJc/s1000/antena7.jpg)
New:
(http://lh4.googleusercontent.com/-7e09tjouTmg/Ub2ZWKtWCJI/AAAAAAAAMqM/b0tBASl2P_A/s1000/antena8.jpg)
The on reverse order fit all together BUT! be careful if put back that metal sh*t cover back. I drop it inside that small area under the antenna and there hopefully was small U-shape hole that i pull it through via wire.
Good luck!