dshelley,
When an external antenna is plugged into the iFly, it shunts the internal antenna, so it must be working a little bit. However based on your description, I'm guessing the antenna is not compatible. It's an active / powered antenna, the one we provide is tuned to work specifically with the iFly chipset, and other antennas will have different specs. So you may want to consider getting the iFly antenna.
Thanks,
Walter