For example, a TV picture having 5 MHz of bandwidth and 5 MWatts of power could not be detected beyond the solar system even with a radio telescope with 100 times the sensitivity of the 305 meter diameter Arecibo telescope. Minimum signal processing is assumed. On the other hand, integration of the data does not make sense for time-varying signals since this would distroy the information content of the signal. This is a basic equation that one can use to estimate SETI detection ranges.
Interstellar space contains a plasma.
Its effects on a propagating radio wave including broadening the bandwidth of the signal. The magnitude of the effect is direction, distance, and frequency dependent, but for most lines of sight through the Milky Way a typical value might be 0.1 Hz at a frequency of 1000 MHz. Now we are in a position to carry out some simple estimates of detection range. These are shown in Table 1 for a variety of radio transmitters. Tsys in particular, was taken as indicated by the question marks in the table.