Kit 433 mhz- How to improve their range?

Hello

I’m using an RF kit working with two arduinos.

After changing the transmitter for another one module with an antenna, I improved the range up to 50 meters without obstacles.
In the specifications, the say that the range it’s between 500-800 meters.

The receiver haven’t got any antenna because it works better without one ( The antennas that i tried aren’t good antennas)

Anyone have same problems with this kits?

Here I left my tutorial with all the code

And the specifications of the transmitter

http://www.dx.com/es/p/zsd-t3-315-433mhz-ask-high-power-rf-transmitter-module-yellow-228289

Probably the best solution it’s to change the type of transmitters, but I want to explore the limit of this kits and write the conclusions for everyone that use this kits.

thanks everyone