I recently put together a DIY Stratux ADS-B. The GPS performance was OK (5 or 6 satellites), but not great. I adding an external GPS antenna clipped onto the internal USB GPS module with an iPX connector which was a little better (8-9 satellites). So there were two competing antennae, the internal and the external. I presumed that the two antennae might compete with out-of-phase signals. I removed the internal antenna from the USB board and increased the number of satellites I receive with usable signals to 19 or so... all with much better signal strength. I also shortened the cable for the external antenna from about 7 to about 3 feet so it is less cumbersome. Very happy with the mods.
Larry
Larry