I am trying to catch swarms myself. I almost, had one last year, and had tried the year before. In response to what I observed last 2 seasons, I have several set up at different heights (from 2m up to 5m) & distances (from 25m t0 150m) from existing colonies. I also reduced the number of frames of foundation, so that when they measure the space it will have a greater volume.
Has been a bit of discussion here
http://forum.honeyflow.com/t/a-huge-swarm-turning-up/8292/37
Good luck!