I've bought a Microstax GPS unit which I'm using directly on my RPi 3 (no Microstax headerboard). I've got the unit connected correctly though I'm strangely seeing a few seconds of correctly formatted NMEA GPS data then the majority of which is just garble which will return a few seconds of NMEA data, then garble again.
I've replaced cables and the like - not sure what it could be other than the unit not getting enough power from the Pi 3.3v rail (it's only supposed to draw 20mw). Any ideas? Stumped.