hello.. i am a newbie…
in Siemens BTS240XL, if you need to use more that 4TRX’s per sector, you can use an extension rack and you can connect an extension rack to main rack by using selic & can bus cable. No need an extension antenna. except you upgrade your GSM with add DCS site on this GSM site..
About the degradation of KPI, maybe you can check the performance of hardware or the frequnecy
CMIIW..