I have this small TX which is meant for a Sony Ericsson mobile phone.

It has a internal antenna on the tiny board where the red arrow is pointing to but what i want to do is add a connector for a proper antenna.

Could i use something like this

and cut one end off and add it to the board where the internal antenna hole is, would that work to get the signal out of a proper antenna?
If not how could it be done.

hello yes that is the antenna pad the big circle is the ground earth and the small circle is the main there is some info on the internet i see if i can send you the link ..

there a lot of info on the net just type diagram for sony ericson transmitter

I know about the boards diagram, what I'm asking is how best to go about adding a bnc connector to the board?

You can't. The board is far too small.

Why add the bnc and coax? It might not even be 50 ohm output so not sure it makes sense to use any coax here. Just add some longer wires and make a little dipole straight from it?

Found this image of the TX which has some connector soldered onto the antenna pad what connector is it?

Can anyone shed some light on this?

That isn't a connector, it's a screw fixing.

If you got a surface mount U.FL connector and carefully cut the pin off of the bottom, you could probably solder it to the antenna pad by filling the via with solder to connect the centre pin. Remember to cut the tracks that form the on-board antenna to disconnect it. But be careful, the impedance of the transmission line to the pad and at the pad is probably not 50 Ohms.

Or, probably easier than fiddling around with tiny connectors, and certainly easier than the mess with all the wires all over the place - lay out your own version with a proper U.FL connector position. It wouldn't be difficult - you've already got the schematic and all of the correct footprints for the components. Use a hot air gun to get the Atmel IC and the RF module off - the rest you can get off using a pair of soldering irons.