The International List of Radio Stations of the World (edition in English) can be procured from the International Bureau of the Telegraphic Union (Radiotelegraphic Service), Berne, Switzerland. In addition to the information contained in the list of the United States stations published by the Bureau of Navigation, the international list shows geographic locations, normal ranges in nautical miles, radio systems, and rates. Supplements to the international list will be issued monthly and will contain new stations and tables of alterations. Inquiries as to the subscription prices of these lists should be made direct to the Berne bureau at the address given above. Remittances to Berne should be made by international postal money orders.

Time signals.-In connection with the service over the land telegraph lines time signals by radio are sent daily, Sundays and holidays excepted, from certain United States naval coastwise radio stations on the Pacific coast and at Honolulu, as follows:

The signals begin at 5 minutes before the hour and continue for 5 minutes. During this interval every tick of the clock is transmitted except the twenty-ninth second of each minute, the last 5 seconds of each of the first 4 minutes, and finally the last 10 seconds of the last minute. The time signal is the beginning of the dash after this long break. Hydrographic information, weather reports, and other information of benefit to shipping are sent out from these stations.

Radiocompass bearings.-The increasing use of radio directional bearings for locations of ships' positions at sea, especially during foggy weather, has made it particularly desirable to be able to apply these radio bearings sent out by the shore stations directly to the nautical chart. The radio bearings sent out by radiocompass stations are the bearings of the great circles passing through those stations and the ship, and unless in the plane of the Equator or of a meridian, would be represented on a Mercator chart as curved lines. Obviously it is impracticable for a navigator to plot such lines on his chart, so it is necessary to apply a correction to a radiocompass bearing to convert it into a Mercator bearing; that is, the bearing of a straight line on a Mercator chart laid off from the sending station and passing through the receiving station,

83405-26-2

On page 14 is given a table of corrections for the conversion of a radio bearing into a Mercator bearing. It is sufficiently accurate for practical purposes for distances up to 1,000 miles.

The only data required are the latitudes and longitudes of the radiocompass stations and of the ship by dead reckoning. The latter is scaled from the chart and the former either scaled from the chart or taken from the list of radiocompass stations printed in the Coast Pilots or in the publication, Radio Aids to Navigation (H. O. No. 205), issued by the Hydrographic Office, United States Navy. The largest scale chart available should be used for this purpose.

The table is entered with the difference in longitude in minutes between the ship and shore station (the nearest tabulated value being used), and opposite the middle latitude between the ship and shore station (to the nearest tabulated value) the correction to be applied is read.

The sign of the correction, when bearings are read clockwise from north, will be as follows: In north latitude, the plus sign is used when the ship is east of the compass station; the minus sign is used when the ship is west of the compass station; in south latitude, the minus sign is used when the ship is east of the compass station; the plus sign is used when the ship is west of the compass station. If the radio bearings are observed on the ship, the signs will be reversed. The corrected bearing is then the Mercator bearing from ship to the sending station, and to facilitate plotting 180° should be added to it and the result plotted from the sending station.

Should the position by dead reckoning differ greatly from the true position of ship as determined by plotting the corrected radio bearings, a retrial should be made, using the new value as the position of the ship.

Example. A ship in latitude 37° 20′ N., longitude 69° 20′ W., by dead reckoning receives a radio bearing of 64° from a radiocompass station located in latitude 35° 14' N., longitude 75° 32′ W. Find the Mercator bearing of the ship from the station

Radiocompass station latitude_.
Dead reckoning position of ship--

Middle latitude___

35° 14' N., long. 75° 32′ W.
37 20
69 20
Diff. 372'

36 17

Entering table with difference of longitude=360', which is the nearest tabulated value to 372' and opposite 36° middle latitude (the nearest tabulated value to 36° 17') the correction 106' is read. The ship being east of the station the correction is plus. The Mercator bearing will then be the radio bearing received plus the correction from the table, 64° 00'+106′-64°+1° 46′-65° 46′.

For more accurate determinations the following formula should be used and on which the table of corrections are based.

Formula for the conversion of radio bearings into Mercator bearings. The Mercator bearing is equal to the radio bearing received, plus or minus one-half the convergence of the meridians in minutes, which expressed as a formula is

M-Mercator bearing required.

R=radio bearing received from the radiocompass station.

D difference in longitude, in minutes, between the radiocompass station and the ship's position by dead reckoning.

B-latitude of the radiocompass station.

B'=latitude of the ship's position by dead reckoning.

Example.-A ship in latitude 37° 20′ north, longitude 69° 20′ west by dead reckoning receives a radio bearing of 64° from a radiocompass station located in latitude 35° 14' north, longitude 75° 32′ west. Find the Mercator bearing of the ship from the station. By the formula

Substituting these values in the formula, and observing that since the ship is in north latitude and east of the radiocompass station, the + sign is used (see p. 12 for determination of signs), we have—

M=64° +186' × 0.59176=64° +110′ = 64° +1° 50′ = 65° 50'

Table of corrections, in minutes

[Difference of longitude in minutes)

Mid. L

06

30 60 90′ 120 150 180 210 240′ 270 300 330 360 390 420 450 480 510 540 570' 600'

Accuracy of bearings.-The accuracy with which bearings can be taken depends on the conditions outlined below; but, although in general the bearings taken by a station within the sector of calibration can generally be considered accurate to within 2°, the Government can not accept any responsibility for consequences of a bearing's inaccuracy.

It is pointed out that if at least 3 radiocompass stations can be employed and if they are situated so as to give good intersections, considerable reliance can be placed on the result of 3 simultaneous bearings thus obtained, provided that the "triangle of error" formed by the bearings is small.

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 half an hour before sunset and half an hour before sunrise, are generally unreliable, on account of the excessive error introduced. These errors are not so great when only an expanse of sea separates the two stations, but in the case of the bearing passing over land, particularily if it is hilly country, the amount of error is abnormal. Changes in the intensity of the signal received also occur at sunset and sunrise, and apart from the above-mentioned variations, changes in the signal strength of the transmitting station have been observed at these times.

Bearings signaled as "approximate" or "second class" must be treated with grave suspicion, as very considerable errors may exist in such bearings.

The following radiocompass stations will be of use for vessels navigating on the Pacific coast. In plotting bearings furnished by these stations the position of the receiver must be used. Vessels equipped with 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 the transmitter must be used for plotting.

2 The calibrated area between 135° and 160° is overland, and bearings in this sector should therefore be used with caution until several months of checking have shown what accuracy may be expected there. 3 The San Francisco entrance stations are under the control of Point Montara radio station. Point Montara will obtain bearings from the remaining stations in the group and furnish them to the ship after corrections have been applied.

4 Bearings furnished in the sector 232° to 264° should be used with caution until reported unreliability has been investigated.

5 Limited service. Standing watch during thick and heavy weather.

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.