Sequenced beacon--main & backup transmitters with controller rack in the centre.
The sequenced radio beacon equipment was devised as an assistance to mariners. For example three radio beacons could be scattered along the coast all transmitting on the same frequency in sequence. Only one beacon would be transmitting at any one time. A navigator could tune his radio direction finder to the sequenced beacon frequency in his area and, as each beacon transmitted for its allotted 1 minute interval, could note the bearing of each.
Applying the bearings to his chart the navigator could be assured his position was where the three lines intersected, sometimes call the 'cocked hat', as they seldom intersected, but usually came close, leaving a small triangle of error--hence the name. If the beacons were not sequenced, they would be transmitting continually on, in this case, three different frequencies, requiring the navigator to tune to each station in turn. Sequencing was economical on frequencies used, and reduced navigator error.
Each beacon had its 1 minute transmit window, thus it was important to ensure the mechanical clock timing was accurate to ensure only one station was ever on at any one time. The station's clocks were checked regularly against the time 'ticks' from the US Navy Station at Arlington, Virginia. Thus the requirement for a good receiver.
The illustration shows the new receiver for use on Beacon Stations.
At the bottom left of the panel is located the filament switch plunger which must be pulled out to put the set in operation. Always push the plunger in after using the receiver. At the bottom right of the panel the phone jack, marked “output”, is located. The head-phones should be plugged into this jack. At the top centre of the panel is located the range switch. When this switch is in the “short” position the receiver will function from 500 to 730 meters, and the “long” position gives a wavelength range from 2,400 to 3,000 meters. The reaction is controlled by the knob in the centre of the panel, while the aerial tuning is controlled by the left hand dial, and secondary tuning by the right hand dial.
The aerial tuning may vary greatly on different stations and the Secondary tuning will vary slightly, but on a standard aerial the Secondary tuning dial, for reception of NAA (Arlington) time signal, should be set at approximately 36 with the range switch in the “long” position. The aerial tuning and reaction controls may be in the neighbourhood of 55 and 40 respectively, but these adjustments may vary greatly according to local conditions. Arlington should be received at good volume by all East Coast and Great Lakes Stations, and over the entire length of its two ranges the receiver should be found sensitive and easily controlled.
The battery connections are made to suitably engraved binding-posts at the back of the receiver. The receiver is intended to use UX201B tubes with an A battery of 6 Volts. The B battery should consist of two 45 Volt blocks.
Arlington Time Signal
Commencing at 11:55 a.m. E.S.T., NAA sends a series of 29 dots at intervals of 1 second. This makes the 29th dot coincide with 28 seconds past 11:55. On the 29th second there is no dot, but commencing at the 30th second NAA sends a series of 25 dots at intervals of 1 second. This makes the 25th dot of the second series coincide with the 54th second past 11:55. No dots are made on the 55th, 56th, 58th and 59th seconds, but at 11:56 NAA commences another series of dots. Each minute thereafter until 12 noon is similarly marked with the exception of the second series of dots in the last minute preceding the hour. Commencing at 11:59 ½ NAA sends a series of 20 dots at intervals of 1 second, the 20th dot coinciding with the 49th second of the last minute before the hour. From the 50th to 59th seconds NAA is silent and on the 60th second—12 noon E.S.T.—he makes a dash. This completes the time signal, which is repeated at 9:55 to 10 p.m., E.S.T.
The photos and instructions on this page are from the "Operating Instructions for Automatic Radio Beacon Equipment--Department of Marine, Radio Branch 1930". This is a three tube regenerative receiver: one detector and two stages of audio amplification. The following italicised text is taken directly from the equipment manual and gives some insight on receiver tuning. In the photograph the three vacuum tubes have been removed for clarity--the four pin sockets remain.
General coverage receiver
Typical beacon Battery charging panel