Nighthawk M2 External aerial

Recently bought an M2. We took it with us touring Southern Australia in our caravan. A friend gave us as a gift an external aerial. I can't tell you the model but it is a stick like antenna with a 5 metre lead and a TS9 patch cable. Reading the result under status menu in dBm made no difference wether connected or not.

On returning to Perth I took it all in to an Antenna specialst who attached the areial to a measuring meter and got very good results just with it sitting on the counter. It went from -91 dBm RSRP (4g) signal to -61 dBm. 

He then tried a much better aerial with the patch lead on my Nighthawk and still got no variation in the status.

I'm guessing it's unlikely both ports are faulty as it's brand new and we tried two other TS9 patch leads incase mine was faulty.

Any help or suggestions would be much appreciated.