Z wave range

Im currently using a raspberry with Z-Wave gpio but I think radio range is a little low.

Is there a simple way to extend it or can someone suggest another Z-Wave controller supported by OH2 that have better radio range. Maybe a antenna

One nice thing about zwave is its mesh networking and the mesh networking works well with the newest zwave binding. Any mains device acts as a repeater, so I think a simple wall plug is as good a way to reinforce the network as a specific repeater device.

You can also improve range sometimes by moving the zwave controller nearer the centre of your house, moving it to a place with fewer walls to traverse and so on. Zwave plus devices have a better range than the older ones, so long as your controller is also zwave plus.

SimonJ has good points. You can get plugin extenders in a pinch but for the price, I would rather just buy an outlet or more light switches to put in other rooms. This will beef up your mesh like the extender would but with the benefit of having more controlled devices.

I use a vera edge with the mios binding for my zwave which is slightly different. I have it in the far basement corner. I can’t see even half of the devices in my network but they all work flawlessly with little to no latency due to a strong mesh. I have an outlet and switch in a detached garage over 100’ from the controller and they switch instantly over 3 hops.

Well, it depends on the special situation you are using it. In my old home I would have agreed to @SimonJ and @Moxified , but in my new house with massive concrete between the floors Z-Wave Mesh came to its limit.
I now use 3 Z-Wave Sticks on 3 different locations building 3 networks. OH is connected to each stick by USB over IP. With this architecture it works flawless. From my experience I would say that up to 15 meters indoor on the same floor works fine and you should try to keep < 100 devices per controller. I am using Aeon Z-Wave Stick Gen 5.