just a question

my question is, we have this 3 camera set up with a video switcher in analog, is it possible if i'm going to use the analog to sdi converter, so that my program out for the whole system will be on an SDI format?

For switching / mixing analog sources you need a mixer for analog sources.

When you use an analog2SDI-converter, you have to connect its output to a mixer with digital inputs.

Attention: Read the manual of your mixer !!! "Digital mixer" often means, that it processes digitally but in- and outputs are analog !

Blackmagic ATEM mixers have only digital in- and outputs (OK, the 1ME has 1 abnalog input....)