help with increasing range of tx/rx

i have a pair of ask tx/rx abt 334 MHz whose range i guess is about 50 mtr.this pair is the standard one provided by himark.these are used with holtek encoders -decoders to make remote control.i wanted to increase the range of these to say about 1 km.can anyone suggest me something.i thought if i could use a power amplifier at the output of tx.will that work.but again the problem is which amplifier will work at that frequency.plz help.

In theory, you can add a 1-5W amplifier (example attached), use better antennas at both ends and 1km distance shouldn't be a problem ..
In practice, increasing the output power of your RX/TX won't be that simple, but if you would like to try - feel free to do so ..
This amplifier is described in http://www.qsl.net/sv1bsx/5w_vhf/5w_vhf.html and was designed for 2m-band so in your case - 334MHz - will need different Ls and Cs ..

Regards,
IanP