The longwave wavelength of 2500 meters used by the navy's radio station NAA in Arlington, Virginia corresponded to a frequency of 120 kilohertz. 360 meters was the standard wavelength used by U.S. broadcasting stations at this time -- it corresponds to a frequency of 833 kilohertz on the AM (mediumwave) band. From 1923 to 1933, NAA would be assigned its own standard broadcasting frequency, of 690 kilohertz.
Sandusky (Ohio) Register, July 30, 1922, page 24:
How the EXACT TIME Is Broadcasted by RADIO
RADIO fans throughout the country have become accustomed to the idea of setting their watches and clocks by wireless each day at 12 o'clock noon or 10 P. M., Eastern standard time, but scarcely one in a thousand knows just how the exact time is broadcasted daily at these two hours.
These time signals, as they are called, are sent out by wireless from the government station at Arlington, Va., over a high-power radio telegraph transmitter which operates at 2500 metres wave length. The time signals are controlled by wire line from the United States Naval Observatory and represent the exact time as registered by a chronometer at that point.
The Arlington time signals are retransmitted by many of the broadcasting stations. For example, if a few minutes before 10 o'clock at night (Eastern standard time) you are listening some evening to W. J. Z. radio station at Newark, the program is interrupted and you hear announcer say:
"Please stand by for Arlington time signals which will now be retransmitted, with final dash for 10 o'clock."
Then promptly at 9:55 the listener will hear a succession of buzzes, each of which is an electric impulse being transmitted every second over the wire line to Arlington. Each impulse results in the radiation of a Morse dash by wireless, and thus a listener using a receiver tuned to the wave length of 2500 metres will hear a series of dashes exactly one second apart as Uncle Sam's master clock ticks them off.
The radio enthusiast whose receiving set will not tune above 700 metres can hear the Arlington time signals perfectly since they are retransmitted on a wave length of 360 metres by the important radio telephone broadcasting stations through out the country.
The following explanation is given of the manner in which the Arlington time signals are broadcasted:
From the zero second of 9:55 P. M., for example, a dash is transmitted each second until the 28th second, the 29th second being marked by the omission of one dash of the series. On the 30th second the dashes begin again and continue until the 54th second, the five dashes running from the 55th to the 59th second also being omitted. On the zero second of the next minute the dashes begin again and the same routine is carried forward until the end of the 59th minute.
For the last minute before the hour 29 dashes are transmitted (beginning at zero), the dash corresponding to the 29th second is omitted, and 20 dashes beginning with the 30th second and running to the 49th second, are transmitted. The 10 dashes, which would correspond to the 10 seconds from the 50th to the 59th inclusive, are omitted. After this pause of approximately 11 seconds a longer dash (which the announcer at the radio station calls the "final dash") is sent out marking the exact hour of 10 P. M., Eastern standard time.
For broadcasting the time signals at noon the same procedure is followed.