We have had the Doran for about a year and half or more. We have never had a problem getting a signal from the tires. We don't use any other antenna. Just the little thing that is on the monitor that came with it.
Works great! I believe they have improved them from before we got ours.
Dusty & Don ... Two spoiled schnauzers and a Maine Coon cat. 2500 Dodge Diesel 2003,SLT,
Bedsaver, Doran tire pressure moniter.
2004 Montana 3295. Fireplace,Washer/dryer,2 air conditioners.
http://photobucket.com/albums/y250/Dustytuu/