Radiobeacons (fog signals).-Radiobeacons operated by the United States Lighthouse Service in or near the section covered by this volume are listed in the following table : 4 dashes (60/120) -. 1 dot and 2 dashes (60/ 41 121⁄2 72 061⁄2 1 dot and 3 dashes (60/ 41 03 73 06 15). 1 dot, 2 dashes and 1 dot (60/30). 40 522 73 441⁄2 1 dash, 1 dot and 1 dash (60/15). 2 dashes (60/120) Single dots (60/120) 3 dashes (60/120) Second 15 minutes of each hour. 4.30 to 5 and 10.30 to 11, a. m. and p. m. 11 p. m. to 1 a. m. and 12 noon to 12.30 p. m. 2 to 2.30 a. m., 12 noon to 12.30 p. m., and 8 to 10 p. m. 5 to 6.30 a. m., 12 noon to 12.30 p. m., and 6.30 to 7.30 p. m. 5.30 to 6 and 11.30 to 12, a. m. and p. m. Second 15 minutes of each third hour, beginning at midnight (3, 6, 9 a. m., 12 noon, 3, 6, 9 p. m.). 12.30 to 1 and 6.30 to 7, a. m. and p. m. 2 dots and 2 dashes (60/ 4.30 to 5 and 10.30 to 11, 120). 1 dot and 2 dashes (60/5 36 551⁄2 70 001⁄2 1 dash, 1 dot and 1 dash (60/120). a. m. and p. m. to 4.30 and 10 to 10.30, to 5.30 and 11 to 11.30, a. m. and p. m. 2 to 2.30 and 8 to 8.30, a. m. and p. m. Third 15 minutes of each hour. 1 Sending and silent periods indicated in parentheses; thus Nantucket Lightship transmits for 60 seconds and is then silent for 120 seconds. 2 Radio operator stands watch on 500 KC/s (600 meters) for the first 15 minutes of each hour from 8 a. m. to 9.15 p. m. (until 10.15 p. m. on Nantucket Shoals Lightship) in clear weather. Station will transmit signals for reasonable additional periods upon request. 3 Radio operator stands watch as noted above and also from 10 to 10.15 a. m. and from 4 to 4.15 p.m. during foggy weather, at which intervals the radiobeacon is not operated. NOTES. (L) indicates light station; (LS) indicates lightship. Except for stations that transmit only on request or are silent for certain watch periods during thick weather, as noted above, transmission is continuous during thick or foggy weather. Signals are also transmitted at certain periods during clear weather as noted in the table. Stations 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 radio compass. By use of this radio compass (also termed radio direction finder) the bearing of the radio fog-signal station may be determined with an accuracy of approximately 2° 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 direction-finding 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 in tensity 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 radio compasses calibrated at all times. This may be done during clear weather by comparing the bearing obtained with the radio compass with the bearing as given by other methods in general use. All radio compasses are subject to what is called "night effect," an indeterminate error sometimes experienced near nightfall and sunrise. The signals from the stations 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. During thick or 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, 32 seconds apart, 12 seconds silence, six 1-second blasts, 312 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. 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. United States naval radio-compass 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 radio-compass 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.) Radio-compass stations are divided into two classes: (a) Single stations, operating independently and furnishing a single bearing. (b) 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. In some cases individual stations of a group are available for independent bearings and for use as radiobeacons. Where only one radio-compass 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 radio-compass 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 radio-compass stations ordinarily will not be guarding this wave. Ships are requested to confine their requests for 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 radio-compass stations will be continuously guarding the 375-kilocycle (800-meter) wave. Calling a radio-compass station. To obtain a bearing from independent radio-compass 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 The following radio-compass 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 radio compass may also use these stations as radiobeacons. 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. 1 New York entrance group; Fire Island, master station. Bearings from Manasquan unreliable at present. 2 Delaware Bay entrance group; Cape Henlopen, master station. 3 Chesapeake Bay entrance group; Virginia Beach, master station; Poyners Hill also available for independent bearings and for use as radiobeacon. 4 Hatteras group; Cape Hatteras, master station; stations also available for independent bearings and for use as radiobeacons. NOTES.-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. Procedure in detail.-(a) A ship calling the radio-compass station or compass-control station should make the abbreviation "QTE?" ("What is my true bearing?"). This request will be answered by the radio-compass 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. (b) The testing should be made on 800 meters, upon the completion of which the ship should await reply from the radio-compass station. (c) The radio-compass station or control station will then reply, repeating the abbrevation "QTE" ("Your true bearing from was 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 radio-compass station, and then the time group, giving the time of the observations in local standard time. In the case of more than one radio compass 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 observation. 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 radio-compass 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 correction 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 radio-compass 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 radio-compass 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 radio-compass stations. 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. 66 In the case of bearings which cut the coast line at an oblique angle, errors of from 4° to 5° 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. 66 Reports. In order that the operation of shore radio-compass 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 radio-compass 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. |