Bandpass filters are widely used in wireless transmitters and receivers. Wireless power transfer may be used to power up wireless information transmitters or receivers. Antenna tuners are particularly important for use with transmitters. Atomic clocks are installed at sites of time signal radio transmitters. An ultrasonic anemometer has two or three pairs of sound transmitters and receivers. Each device may contain one or more HDCP transmitters and/or receivers. These are sometimes used as the pulsed power sources for radar transmitters and other devices. This had rendered all existing FM transmitters and receivers obsolete. The controls within the zone may cover elements other than radio transmitters or radio devices. The company manufactured both transmitters and receivers. Real-world transmitters and receivers usually are directional. Canada has no longwave time signal transmitters. These parameters are useful in the characterization of electronic devices, such as wireless transmitters. Real-time propagation can be assessed by listening for transmissions from specific beacon transmitters. These channels are relayed by all terrestrial transmitters in India.