Increase the VM109 range to more than 800m

I recently bought a VM109 Remote control set. I attached a directional UHF antenna to the receiver and increased the range to about 100m. I attached an antenna to the transmitter and increased the range to about 800m. I need another 200m. I attached both the signal and ground to the receiver, but I could only attached the signal wire to the transmitter. I can’t attach the ground of the arial to the negative of the battery in the transmitter, it shorts out something. I would like to know were is the correct place to connect the arial to the transmitter, both the signal and ground? Is there any other way to increase the power of the transmitter?

Sorry, we do not have any experience with external antennas.

That’s alright, I don’t need need someone like that, I need the circuit diagram for the transmitter to know were the antenna and the ground is to connect the cable signal and shield to. I think that the signal strenght gets reduced because the shielding of the coax cable is not connected. Or could you tell me if you have any circuit diagrams or modules for a small RF amplifier? For instance, can I use a u741 Op-Amp or another Op-Amp (high speed) to amplify the signal? Do you have circuit diagrams (or know were I can find one) for this and can you tell me where this should connect to the transmitter? Is there any other stronger transmitters that work with the VM109 receiver?

Diagram can be found here:
http://www.velleman.eu/downloads/0/illustrated/illustrated_assembly_manual_k8059_rev1.pdf
Sorry, no other circuits or products.

Thanks, is there anyone there that can tell me were to put the Op-Amp in?