nkuck:
What I am trying to do is utilize the output from your sketch as a loop antenna that I can then detect by a secondary coil or loop.
You'd best keep the power level extremely low, or you could easily be in violation of FCC regulations (or the radio regulations of your country if it's not the USA), and/or interfere with local radio services. Even with a loop antenna. Also your square wave signal will splatter RF sidebands all over the place, not just at 4Mhz.