WOW signal - Interpretation of the paper chart
The circled alphanumeric code 6EQUJ5 describes the intensity variation of the signal. A space denotes an intensity between 0 and 1, the numbers 1 to 9 denote the correspondingly numbered intensities (from 1.000 to 10.000), and intensities of 10.0 and above are denoted by a letter ('A' corresponds to intensities between 10.0 and 11.0, 'B' to 11.0 to 12.0, etc.). The value 'U' (an intensity between 30.0 and 31.0) was the highest detected by the radio telescope, on a linear scale it was over 30 times louder than normal deep space. The intensity in this case is the unitless signal-to-noise ratio, where noise was averaged for that band over the previous few minutes.
Two different values for its frequency have been given: 1420.356 MHz (J. D. Kraus) and 1420.4556 MHz (J. R. Ehman). The frequency 1420 MHz is significant for SETI searchers because, it is reasoned, hydrogen is the most common element in the universe, and hydrogen resonates at about 1420 MHz, thus extraterrestrials might use that frequency on which to transmit a strong signal.
The frequency of the Wow! signal matches very closely with the hydrogen line, which is at 1420.40575177 MHz. The two different values given for the frequency of the Wow! signal (1420.356 MHz and 1420.4556 MHz) are the same distance apart from the hydrogen line—the first being about 0.0498 MHz less than the hydrogen line, and the second being about 0.0498 MHz more than the hydrogen line. The bandwidth of the signal is less than 10 kHz (each column on the printout corresponds to a 10 kHz-wide channel; the signal is only present in one column).