Remember that in North America, anything in the 700 MHz band is now illegal:
"The operation of wireless microphones and similar devices is prohibited from certain frequency bands for public safety reasons and commercial concerns. The sale of wireless microphones or similar devices intended for use in the United States in the 700 MHz Band was banned by the FCC in January 2010, and use of the devices in the 700 MHz Band was prohibited as of June 12, 2010. “Similar devices” include wireless intercoms, ear monitors, audio instrument links and cueing equipment.
The 700 MHz Band – between 698 and 806 MHz -- is now reserved for use only by public safety groups, such as police, fire and emergency services, and commercial providers of wireless broadband services. Use on broadcast bands outside of the 700 MHz Band was not affected by the ban, and can continue..."
http://www.fcc.gov/encyclopedia/wireless-microphones