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120 seconds.

Ambrose Channel Lightship (call letters WWAT):
Single dashes

60 seconds. Silent-

Clear weather transmission: 3.30 to 4 and 9.30 to 10, both a, m, and p. m. NOTE.—Ships for which no call letters are given do not maintain radio communication.

These radio fog signals are intended for the use of vessels equipped with radiocompass. By use of this radiocompass (also termed radio direction finder) the bearing of the radio fog-signal station may be determined with an accuracy of approximately 2o and at distances considerably in excess of the range of visibility of the most powerful coast lights. The apparatus is simple and may be operated by the navigator without the assistance of a radio operator or without knowledge of the telegraph code. The radio directionfinding apparatus consists of a radio receiving set, similar in operation to those used for radio telegraph or telephone reception, and a rotatable coil of wire in place of the usual antenna. By rotating the coil the intensity of the signal received from the transmitting station is caused to vary, and by noting the position of the coil when the signal is heard at its minimum intensity the bearing of the transmitting station is readily obtained.

It is important to note that the bearing of an incoming radio wave is subject to errors not unlike the deviation of a magnetic compass. Those using radio direction finding on shipboard are cautioned to bear these errors in mind and to keep radiocompasses calibrated at all times. This may be done during clear weather by comparing the bearing obtained with the radiocompass with the bearing as given by other methods in general use. AÎl radiocompasses are subject to what is called “night effect,” an indeterminate error sometimes experienced near nightfall and sunrise.

The signals from the lightships have definite characteristics for identifying the stations, as have the flashing lights and sound fog signals, and bearings may be obtained with even greater facility than sight bearings on visible objects. The radio fog signals are transmitted on a wave length of 1,000 meters, which is exclusively reserved for this purpose to avoid interference.

With the exception of Nantucket Shoals Lightship, as noted below, the lightships transmit continuously during thick or foggy weather, and sound the signal daily in clear weather during certain periods as noted above (seventy-fifth meridian time).

On Nantucket Shoals Lightship (call letters WWAH) the operator stands watch in clear weather during the first 15 minutes of each hour (seventy-fifth meridian time) from 8 a. m. to 10.15 p. m. During fog the radiobeacon will be silent from 10 a. m. to 10.15 a. m. and 4 p. m. to 4.15 p. m. for listening in.

During thickor foggy weather Nantucket Shoals Lightship sounds radio fog signals and submarine signal at the same time. The submarine signal sounds 2 groups of blasts every 90 seconds, thus, six 1-second blasts, 312 seconds apart, 12 seconds silence, six 1-second blasts, 31/2 seconds apart, 31 seconds silence. In each repetition the first dash of the radio signal and the first blast of the submarine signal are sounded at the same time. The difference in time in seconds between the reception of the first dash of the radio signal and the first blast of the submarine signal multiplied by 1,600 will give the distance in yards of the observer from the lightship.

Vessels are requested to forward reports to the Commissioner of Lighthouses, Washington, D. C., or Superintendent of Lighthouses, Boston, Mass., as to the effectiveness of this signal.

Operators on Fire Island and Ambrose Channel Lightships maintain watch on 600-meter wave for the first 15 minutes of each hour from 8 a. m. to 9.15 p. m., local standard time, except when radiobeacon is in operation. Requests by radio for special transmission of signals for testing or calibrating should be made during such watch periods, using 600-meter wave.

A general description of this method of navigation and the instruments required is given in Lighthouse Service Publication, Radio Fog Signals and Their Use in Navigation, which may be obtained from the Superintendent of Documents, Government Printing Office, Washington, D. C., for 10 cents. Bureau of Standards Scientific Paper, No. 428, The Radio Direction Finder and Its Application to Navigation, may be obtained from the same source for 15 cents.

Accuracy of bearings.—The accuracy with which bearings can be taken depends on various conditions and, while bearings taken by a station can generally be considered accurate to within 2°, the Government can not accept any responsibility for the consequences of a bearing being inaccurate.

When three stations, so situated as to give intersecting bearings. can be used and the three simultaneous bearings cross with a small "triangle of error,” considerable reliance can be placed in the position obtained.

In the case of bearings which cut the coast line at an oblique angle, errors of from 4° to 50 have been reported. Bearings obtained between about one-half hour before sunset and one-half hour after sunrise are generally unreliable. It is probable that the accuracy of a bearing is also affected if the ship's transmitting instrument is not adjusted to the correct wave length. Bearings signaled as “ approximate” or “ second class” should be regarded with suspicion as being subject to considerable error.

United States naval radiocompass stations will furnish radio bearings to mariners of all vessels equipped with radiotelegraph transmitters. While the use of these bearings should not lead a mariner to neglect other precautions, such as the use of the lead, etc., during a fog, these bearings will greatly reduce the dangers to navigation for mariners who are compelled for any reason to proceed during foggy or misty weather.

These radiocompass stations are provided, primarily, to assist the mariner in closing the land during fog or poor visibility, but they may also be used to obtain the positions of vessels at sea in radiocompass range, about 150 miles, when for any reason positions can not be obtained by other means. The maximum distance for which bearings from these stations are accurate is 150 miles. (See preceding pages for reduction of observed bearings to Mercator bearings.)

Radiocompass stations are divided into two classes: (a) Single stations, operating independently and furnishing a single bearing. (6) Harbor-entrance groups. All stations in harbor-entrance groups are connected to and controlled by the master station. All stations of the group take bearings simultaneously and these bearings are transmitted to the ship. requesting them by the control station.

Where only one radiocompass station is available, the mariner may fix his position by two or more bearings, from the station with

the distance run between, or may use the bearings as a line of position, or as a danger bearing. Or the bearing may be crossed with a line of position obtained from an observation of an astronomical body to establish a fix.

Wave lengths.-All independent and group radiocompass stations keep watch on 375 kilocycles (800 meters). Only this wave should be used to call and work with these stations.

Hours of service. During the first 10 minutes of each hour during clear weather radiocompass stations ordinarily will not be guarding this wave. Ships are requested to confine their requests to bearings during clear weather to the remaining 50 minutes of the hour, as far as is practicable. Should a station chance to hear a request for a bearing during the first 10 minutes of the hour, the required bearing will be given. During the remaining 50 minutes, and at all times during inclement weather, all radiocompass stations will be continuously guarding the 375-kilocycle (800-meter) wave.

Calling a radiocompass station.—To obtain a bearing from independent radiocompass stations, call the station from which the bearing is desired in the usual manner and request bearings by means of the conventional signal given hereafter. Simultaneous bearings from two or more compass stations can be obtained by making the call include the other compass stations desired. To obtain bearings from the harbor-entrance compass stations, carry out the procedure previously given. The compass-control station only will answer.

Conventional signals.The following abbreviated signals will be used:

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The following radiocompass stations will be of use for vessels navigating within the approximate limits of this volume. In plotting bearings furnished by these stations the position of receiver must be used. Vessels equipped with a radiocompass may also use these stations as radio beacons. For this purpose a station will transmit, upon request, its call letter for 45 seconds on 800-meter wave. When the bearing is taken on the vessel the position of transmitter must be used for plotting

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1 These stations ordinarily operate as a group, but are also available for independent bearings and for beacon service. The group call is NWM with Deer Island as the master and transmitting station.

NOTE.-The arc of calibration is a sector of the circle of which the compass coil at the radio station is the center; the bearings are from the station (clockwise). Compass bearings are reliable only when they fall within the calibrated arcs.

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Procedure in detail.—(a) A ship calling the radiocompass station or compass control station should make the abbreviation “QTE?” (“What is my true bearing?"). This request will be answered by the radiocompass station or control station, and when ready to observe the radio bearing it will send the signal “K,” indicating to the ship to commence " testing "; that is, repeating its distinguishing signal for a period of 50 seconds. The signal should be made slowly, with the dashes considerably prolonged.

(6) The testing should be made on 800 meters, upon the completion of which the ship should await reply from the radiocompass station.

(c) The radiocompass station or control station will then reply, repeating the abbreviation “QTE" (" Your true bearing froin

--- degrees”), followed by the bearing in degrees given by a group of three figures 000 to 359, indicating the true bearing in degrees of the ship station from the radiocompass station, and then the time group, giving the time of observations in local standard time. In the case of more than one radiocompass connected by land line, only the station originally called will answer. This station will combine all the bearings taken by itself and associated stations into one message, which gives each bearing observed immediately after the name of the station making the observations. All compass stations transmit on 800 meters.

Danger from reciprocal bearings.—Attention is invited to the fact that when a single bearing is furnished there is a possibility of an error of approximately 180°, as the operator at the compass station can not always determine on which side of the station the vessel lies. Certain radiocompass stations, particularly those on islands or extended capes, are equipped to furnish two corrected true bearings for any observation. Such bearings when furnished vessels may differ by approximately 180° and whichever bearing is suitable should be used.

Caution.—Mariners receiving bearings which are evidently the approximate reciprocal of the correct bearing should never attempt to correct these bearings by applying a correction of 180°, as such correction would not include the corrrection necessary on account of deviation at the compass station. An error of as large as 30° may be introduced by mariners applying an arbitrary correction of 180° to such bearings. Vessels receiving bearings manifestly requiring an approximate 180° correction should request the other bearing from the radiocompass station if not previously furnished.

Bearings, except in the case of approximate reciprocal bearings, should be accurate within 2° of arc, provided the transmitting equipment on board vessels is tuned sharply to 800 meters. Operators should use sufficiently wide coupling to obtain low decrement. If radio transmitters are not tuned sharply, it is difficult to obtain bearings that are sufficiently accurate for navigational purposes.

When bearings from three or more compass stations are not over 2° of arc in error, but do not meet at a fixed point, the geometric center of the triangle formed by the bearings can generally be taken as the approximate position of the vessel. Mariners, until thoroughly familiar with the system, are advised to use radiocompass stations frequently, especially in clear weather, when positions of vessels can be accurately fixed in order to accustom operators to the

procedure and to acquaint themselves with the degree of accuracy and dependability of bearings furnished by the radiocompass stations.

Reports.-In order that the operation of shore radiocompass stations may be checked, mariners, obtaining bearings are requested to forward a brief report to the Director Naval Communications, Navy Department, Washington, D. C., containing the following particulars:

1. Name of ship.
2. Name of radiocompass station.

3. Date and local standard time at which radio bearing was taken.

4. Bearings given by radio station.

5. Estimated position of ship at above time and dates by methods other than radio.

6. The probable degree of accuracy of the estimated position.. 7. Weather conditions at above time. 8. Remarks, if any. 9. Signature of master or responsible navigating officer.

There is no charge for bearings furnished by the United States naval radiocompass stations.

Radio telegraphic broadcasts of weather information, issued daily (Sundays and holidays included) by the United States Weather Bureau for the benefit of marine and aviation interests, are sent out in cooperation with Office of Communications, Navy Department, from naval radio stations on the North Atlantic coast.

Bulletins are broadcast from the Arlington (Va.) Naval Radio Station (call letters NAA), as follows:

Wave length, 2,677 meters.
0300 (GCT), time, navigational warnings.
0330 (GCT), weather.
1700 (GCT), time, weather.

1530 (GCT), weather, navigational warnings. Bulletins are broadcast from the Boston Naval Radio Station (call letters NAD), as follows:

Wave length, 2,939 meters.

1600, 2200 (GCT), weather, navigational warnings. Major bulletins.-These bulletins are broadcast from the Arlington (Va.) Naval Radio Station (call letters NAA) twice daily, as follows:

Morning bulletin at 10.30 a. m. (1030) (1530 GCT), on wave lengths of 2,677 and 4,409 meters (133 KC/s) A. C. W. tube.

Evening bulletin at 10.30 p. m. (2230) (0330 GCT) on wave lengths of 2,677 and 4,409 meters (133 KC/s) A. C. W. tube.

The bulletins are divided into two parts and invariably begin with the words “Weather Bureau bulletin." The first part consists of surface weather conditions based upon observations taken at 8 a. m. and 8 p. m. and upper-air data.

Weather reports from ships in the Atlantic Ocean, and during the hurricane season additional ship reports from the Gulf of Mexico and Caribbean Sea, follow the reports from land stations in the first part of the bulletin.

The second part of the bulletin consists of a summary of general atmospheric pressure distribution over land and sea, including the

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