Radio emission generated by human activity can be classified as intentional and unintentional. The former category includes transmitters, radars, and numerous other devices and is the subject of an extensive body of regulations. Many other devices, such as digital computers, electric switches, and radio and television receivers, generate radio emissions as a byproduct of their activity. Still other devices, such as cordless telephones, garage door openers, or home alarm systems, do emit intentionally but presumably at fairly low levels. Both of these categories of devices are only minimally regulated. Such low level radio emissions constitute a major source of interference for radio astronomers and other scientists, who are passive users of the spectrum, in detecting and studying natural radio emissions. The aggregate effect of unintentional radio emitters is to raise the natural noise floor level. This effect interferes not only with passive users of the spectrum but also with a number of other scientific activities which make use of low level radio signals, such as wildlife tracking. That the noise floor has already been raised considerably near major population centers has important implications. Airline pilots, for example, find it increasingly difficult to listen to instructions as they near major population centers. Knowledge of the noise level due to unintentional radiators is important for a number of reasons, such as the planning of interference prevention strategies, prediction of future trends, and documentation of the invasion of such devices into the passive bands allocated to radio astronomy. Measurements are difficult to carry out, however, and are practically nonexistent, except for a few frequency bands of interest to special groups. The Principal Investigator (PI) will obtain such measurements from aircraft, at frequencies allocated to radio astronomy, within the 30-3,000 MHz range, approximately. The PI obtained and published a similar, but less sophisticated, set of measurements in 1972. No other measurements exist to indicate the time evolution of this important activity. The research is of the kind that is fundamental to preserve a sound scientific environment. The PI is very experienced and has a proven track record. An additional strong point is that most work will be carried out by a graduate student. Few researchers are working in this important area and the addition of trained manpower is highly desirable.//
