Complex sentence: About a month before KQIV went on the air the FCC halted any further testing of Quadraplex concerned that the system used a subcarrier component not permitted under its regulations.
Split into simpler sentences: About a month before KQIV went on the air, the FCC halted any further testing of Quadraplex. The FCC was concerned that the system used a subcarrier component that was not permitted under its regulations.