Hi Clinton,
Unfortunately I'm not familiar with the adsbSCOPE 2.6 and GNS 5890. Though can you explain what the false readings are?
Also, what type of antenna do you have? What are its technical specs and what type of connection do you require to your receiver?
There are lots of different antennas available for the use of ADS-B reception on 1090mhz, but it depends on your requirement and setup as to what type you would purchase.
Here's a couple of directional antennas for 1090mhz:
http://www.moonraker.eu/Avionics-and...TIONAL-ANTENNA
http://www.moonraker.eu/Avionics-and...TIONAL-ANTENNA
We're having an ADS-B Workshop in November with other users of ADS-B equipment that you might be interested in attending. You can check out the details here
http://yssyforum.net/board/showthread.php?t=8474