You can download the sources in any directory. For example: /usr/src
cd /usr/src svn checkout http://voip.null.ro/svn/yatebts/trunk yatebts ./autogen.sh ./configure make && make install
Also don't forget to configure Ybts.conf, especially the Band and C0 parameters, which have no default values.
For the detailed steps and prerequisites, please see the Installing page;
The diagram below is a comparison between the software architectures of OpenBTS and YateBTS.