Using a 434MHz PCB Trace Antenna
RF comm is a regulated medium.  There are specific bands in which unlicensed signals may be sent.  Even in these unlicensed bands there are limits on output energy.

Just because the carrier is 434 MHz doesn't mean that all of the energy output will be at that frequency.  For example a square wave has infinite bandwidth.  When a square wave is multiplied by a carrier, it still has infinite bandwidth centred at the carrier frequency.

Real radios need bandwidth filters to ensure that the energy output complies with a spectral mask.  So a square wave will only be parts of a square wave when it goes over the air.

That may be enough in your application.  Or you may want to consider one of the usual RF packet protocols.