heres an example of a Barber Triple Trak which you can make
The instructions for building this can be found in this:
NAR Technical Review, Vol. 6 - Contains articles
on calculation of optimum model rocket mass,
Cineroc film analysis, a two axis open-sight
optical tracker and streamer duration.
Tracking - A collection of articles including altitude
tracking and data reduction, two station tracking,
and the Triple-Track Tracker.
hope this helps