That's the receiver. If that were using the Bluetooth standard transmitted form the detector, then it would have been a great way of carrying any Bluetooth receiver, possibly in the form of say a mobile phone(iPhone or the like) and running your headphones/earphone from that or maybe utilising any other of the off the shelf, after market Bluetooth headphones that have the Bluetooth receiver built in.
Saves you having to carry any extra boxes that you need to some how pocket,on you.
If it were a wifi transmitter coming from the detector(most probably not) but could be , then that to would have been ideal for using on an alternative receiver with the headphones/earphones of choice.
My guess, though I hope it is NOT the case, is that the little Minelab receiver you need to get is propriety to the transmitter of the CTX3030. Most probably so that we get the best possible result from wireless headphones.
There is of course the option to probably use your own transceiver system anyway.....but it's being able to use the built in one that the CTX3030 has that I would like to use instead.
David Di