300 Mhz amplifier

Dear Diego:

Please first consult your authority (Ministry of Telecommunications) if the frequency you chose (300 MHz) is allowed to be used for data transmission.
The 300 MHz band is often used for car, garage openers and the like. You may break the rules and be prosecuted.
Then check for instance the ARRL Radio Amateurs Handbook on how to design a radio equipment, antennas. Transmitting 1 kbps is easy but your equipment should be well designed to operate reliably. If you are a licensed radio amateur, in Argentina you may use 220 MHz or 440 MHz band.