The experiment has only on frame of reference. Two points in space separated by 3 m distance , one representing transmitting antenna and the other one receiving antenna. Transmitter sends a pulse of 1 ns duration and antenna senses the pulse arrival. The digital scope is the observer and records the time of both events with it's extremely accurate clock and digital memory. There is never being an incident in history where pulse would arrive before it was transmitted. Magnetic field is a prime force field and only exists around the source. It's action is instantaneous and it cannot be detached from source and made to travel.
Also how would you apply Lorentz transform to such magnetic field?
Mathew Orman