A roofing filter is a type of filter used in a HF radio receiver. They are received by another antenna attached to a radio receiver. The superheterodyne works like the one in a radio receiver. In case of a radio receiver application, the definition is slightly different. One was Detachment 1, 1962nd Communications Group which operated a radio receiver site. Previously Westinghouse had financed its stations through the profits from radio receiver sales. It is usually used with a radio transmitter or radio receiver. Battery replacement was a major operating cost for early radio receiver users. Crystal radio receivers are a very simple kind of batteryless radio receiver. Thus, there is no deadline by which consumers must buy an HD Radio receiver. There were 84.5 million radio receiver sets (1997). A C-47 that received a radio receiver crashed into the Mediterranean. A SELCAL decoder is connected to each aircraft's radio receiver. The signals are unscrambled by the radio receiver modules, which display the broadcast information. Two important attributes of a radio receiver are "sensitivity" and "selectivity".