  We experimentally realize a meter-scale strong coupling effect between
magnons and photons at room temperature, with a coherent coupling of 20 m and a
dissipative coupling of 7.6 m. To this end, we integrate a saturable gain into
a microwave cavity and then couple this active cavity to a magnon mode via a
long coaxial cable. The gain compensates for the cavity dissipation, but
preserves the cavity radiation that mediates the indirect photon-magnon
coupling. It thus enables the long-range strong photon-magnon coupling. With
full access to traveling waves, we demonstrate a remote control of
photon-magnon coupling by modulating the phase and amplitude of traveling
waves, rather than reconfiguring subsystems themselves. Our method for
realizing long-range strong coupling in cavity magnonics provides a general
idea for other physical systems. Our experimental achievements may promote the
construction of information networks based on cavity magnonics.
