Home » Frequencies » 19 When the Amateur Service is a secondary user of a band and another service is the primary user, this means:   a.   nothing at all, all users have equal rights to operate   b.   amateurs may only use the band during emergencies   c.   the band may be used by amateurs provided they do not cause harmful interference to primary users   d.   you may increase transmitter power to overcome any interference caused by primary users