Heterodyne repeater or cross band repeater: In radio reception and retransmission, a repeater that converts the original band of frequencies of the received signal to a different frequency band for retransmission after amplification.

Radio repeaters usually operate in the FM (frequency modulated) mode and are common in commercial two-way and Amateur (Ham) Radio communications. The repeater devices generally use the VHF and UHF frequency bands and operate using line-of-sight propogation from the tops of mountains, tall buildings and towers, giving small mobile and handheld radios radio coverage for hundreds of miles.

Note: Heterodyne repeaters are used, for example, in microwave systems, to avoid undesired feedback between the receiving and transmitting antennas. Synonym IF repeater.

A repeater can repeat on the same band, but either the transmitting antenna and receiving antenna must be widely separated, or a high decibel filter system such as a series of cavity filters must be used to both block and pass the receception and transmission frequencies for their respective parts of the repeater. See the repeater chapter in The ARRL Handbook for details. Such a system is much more bulky and complex than a cross band repeater.

Source: from Federal Standard 1037C and from MIL-STD-188