Chapter - 21

Radio

While radio is definitely a part of the science of navigation, it has assumed such an important role that it is somewhat a case of "the tail wagging the dog." It is not feasible here, nor in navigation texts, to include more than a general outline of the subject. With these facts in mind, we shall state the principles on which radio is based, and give hints which will serve as a guide for beginners in the yachting field.

Fundamental Principles. The basic principle of radio, as applied to navigation, is that Hertzian waves, sent from a transmitting station, may be detected at a distant receiving station.

A second principle is that the direction from which radio waves are received may be determined to within 1 to 3 degrees by means of the directional characteristics of the loop aerial. This same directional characteristic of a loop is also applicable, to a limited extent, to transmission as well as to reception, thus making it possible to direct the radio waves in a path that diverges only about 10 miles at a distance of 100 miles.

Using the first principle, we have radio communication by Morse code, and the increasingly important radio phone.

The Radio Compass

A radio compass, or direction finder, which gives the direction from which received signals arrive, is merely a useful application of the well-known directional characteristics of a loop antenna, as described in the second principle above. When the edge of the loop is pointed toward the transmitting station, the reception is of maximum strength; and when the direction of the incoming waves is perpendicular to the plane of the loop, little or no signal will be heard.

Therefore, if a dial is mounted on the loop, the direction from which the incoming signal is received may be determined by swinging the loop around, back and forth, until the point of minimum reception strength is found. The point of minimum strength is used because that point is much sharper and easier to detect than the point of maximum receptive strength.

The increasing number, effective range, and accuracy of marine radio aids makes radio navigation an important supplement to the older methods of piloting, dead reckoning and celestial navigation. Radio is used as follows:

1.Radio-compass stations—giving the position (or a line of position) of a ship equipped with sending apparatus, from a shore station or group of shore stations. These stations are diminishing in number.

2. Radio-beacons—giving lines of position to a ship equipped with direction finding apparatus. The number of these stations is increaseing rapidly.

3. Radio-beacon distance finding stations—where a single station by radio and sound signals propagated simultaneously will give both distance and bearing to a receiving ship.

4. Broadcasts of meteorological information and Notices to Mariners.

5. Revolving radio beam—directional radio sending apparatus which sends a sharply directive signal by which a vessel with only a receiving set may determine direction from the station. There are only a few stations of this type in operation.

6. Radio time signals.

Radio-Compass Stations

Radio-Compass Stations. Radio-compass stations, or as they are now termed, Radio Direction Finder Stations, are stations equipped with special apparatus for determining the direction of ships or other stations by their transmitted radio signals. All that is necessary is for a ship to request a position by radio on the proper frequency or wave length and to transmit clearly, distinctly, and with a sharply tuned transmitter on that frequency during the period of taking the bearings. The procedure for U. S. stations (operated by the U. S. Navy) is as follows:

1. Ship desiring bearings calls station from which bearings are desired, on wave length guarded by that station, usually 800m or 375 kc. If more than one station is to be asked to furnish simultaneous bearings, unless the stations are connected by land-wire as a group, each station must be called individually.

2. Shore station (or stations) answers.

3. Ship sends "QTE" (meaning "I wish to know my radio direction finding bearing with respect to the station (stations) called").
4. When ready to take bearing, shore station (stations, if not grouped) sends call letter followed by the letter "K" to the ship.

5. Ship sends its own call letter and other signals during a period long enough for all stations to fix bearing accurately.

6. Shore station (stations) send "QTE" preceded by the time of observation and followed by a group of three figures (000 to 359) showing in degrees the true bearing of the ship with respect to the shore station.

7. The ship repeats the bearing to the shore station, which reports if the bearing was correctly transmitted both ways, or if not, corrects it by repeating the original message. When the shore station is satisfied that the ship has received the bearing correctly, it transmits "End of work," which is repeated by ship before signing off.

The Hydrographic Office publishes two books called "Radio Navigational Aids" (HO2O5) and "Radio Weather Aids to Navigation" (HO2O6) which have in detail all procedure for U. S. Direction Finder Stations and the pertinent data on each station, such as sectors of calibration, latitude and longitude of transmitter and receiver, normal wave length and frequency, hours available, and whether or not the station is one of a land-wire (radio) connected group. They also cover foreign stations working under the General Radio Regulations of the International Telecommmunication Convention of Madrid, 1932. All necessary data are given in these two books, which sell for 90 cents each. These official books contain so much useful information that every ship equipped with a radio should have a copy of each.

Radio Beacons

Radio Beacons. Radio beacons are stations established at lighthouses, lightships, or important points on the coast for the purpose of sending out radio signals in all directions which vessels equipped with direction finders (radio compasses) can use to establish the direction of the radio beam from them. The bearings found in this manner are, as in the case of bearings from shore radio direction finding stations, great circle bearings.

Radio beacons in the U. S. are operated mostly by the Lighthouse Service of the U. S. Coast Guard. They are of three classes: C, B, and A. Ranges are 5-15 miles, 50-150 miles, and 150-250 miles respectively. They cover the coast line much more thoroughly than lighthouses and sound signals, the high-powered beacons being used to guard main approaches to the coast from deep water, the medium-powered being used tor coastwise traffic, and the low-powered for inland waterways and local harbor entrances.

In the U. S., radio beacons operate for one minute out of every three during certain established periods in fair weather, usually two periods of ten minutes each hour. They operate continuously during fog or thick weather, on the basis of one minute on, two minutes off. Certain exceptions to this schedule are covered in the Radio Beacon Charts and Light Lists published by the United States Coast Guard or in H.O. 205, "Radio Navigational Aids." The frequency band used is universally set at 285-315 kc. Sending intervals of United States radio beacons are spaced by what is called "time-synchronization," so that there is no interference between stations in a group of three operating on the same frequency as, by automatic clock control, the signals of adjacent stations do not overlap more than one or two seconds out of a minute.

Distance Finding Stations

Distance Finding Stations. By accurate synchronization a long beat of the fog signal is sent out at definite intervals in exact conjunction with a special long dash by radio from the station. A vessel, knowing the beacon to be equipped for distance determination, starts a stop watch at the end of the dash and measures the seconds until the end of the air sound signal is heard. Sound travels approximately 1 nautical mile in 5.5 seconds, whereas the velocity of radio may be taken as instantaneous.

The Revolving Radio Beam. A new method of obtaining direction by radio is being tried out at a few stations in England at present, in which no radio compass or direction finder is needed on either ship or shore station.

Every time the revolving beam passes true north, a distinctive all-around signal is emitted which all vessels within hearing can pick up. A vessel listening in notes the time at the "north" signal and then marks the time until the very sharp minimum occurs, when the signals fade out temporarily. The time interval between the all-around north signal and the sharp minimum gives the bearing of the vessel from the station.

Sources Of Error

Sources of Error in Radio Direction Finding. The various sources of error in radio direction finding are:

1. Radio bearings are great circle bearings and cannot be accurately plotted as Mercator or plane bearings.

2. Night effect.

3. Land effect.

4. Danger from reciprocal bearings.

5. Errors from local effects, and imperfect calibration.

6. Errors due to atmospheric and other radio interference.

Radio Bearings as Great Circle Bearings. Inasmuch as radio waves travel over the shortest distance from one point on the earth's surface to another, they follow great circles. If a WSN (or Lambert) plotting chart is at hand, the bearing may be plotted as a straight line from the point of reception by the determination of the bearings, as straight lines on these charts are to all intents and purposes great circles.

If, however, a Mercator chart is to be used, the bearing as received must be corrected.

Night Effect. Bearings taken at night, dusk, or dawn are likely to be seriously in error. The reason for this is that part of the signals arrive by reflection from the Heaviside layer. This effect is variable and cannot be predicted. Night effect applies to the radio compass, the radio direction finder and the radio beacon alike, errors from this cause rising as high as 20 degrees or more.

Coastal Refraction or Land Effect. In the case of bearings crossing an intervening coast line or high land between the sending and receiving station, errors as high as 15 degrees may be found. However, under ordinary conditions, no high land will intervene between a vessel and the station it is working with, hence these errors may be dismissed as negligible unless the shore station reports the bearing as dubious.

Reciprocal Bearing Dangers. With merely simple loop reception, it is impossible to tell from the signal itself whether the true bearing or the reciprocal is being received. However, vessels should almost always be able to judge from their dead reckoning positions whether they have received a bearing in the correct quadrant or not, and if not, they should never take the reciprocal of the bearing as their true bearing. Rather they should find the other minimum if operating their own direction finder, or if obtaining bearings from shore, should ask for the other minimum, as, due to differences in calibration curves, the opposite bearing may be as much as 20 degrees away from the absolute reciprocal of the first bearing given.

Errors from Local Effects. No radio direction finding set is entirely free from local influences. These may be in the form of power lines, or "loops" composed of water mains, iron or steel structures, antennas, or powerful sending sets. Aboard ship it is almost impossible to locate a direction finder where it will not be subject to most of the above influences to a considerable extent. However, careful calibration will furnish a dependable error on each heading, and by silencing all other sets while a bearing is being taken, opening the circuits of all antennas and carefully applying the error found from the calibration curves, accurate bearings may be taken.

Shore stations are always calibrated over definite sectors which are given in H.O. 205, and bearings which fall outside them are sent out marked "uncertain." All other bearings sent out by shore stations are corrected bearings and may be depended upon normally within about 2 degrees.

Interstation Interference. (Radio Compass.) It may be found sometimes that stations cannot be sufficiently separated by the radio compass on account of lack of receiver selectivity. This may not be obvious to the user, as the interference may not be audible. Sometimes this effect may be detected by wandering of the bearing.

General Failures. (Radio Compass and sometimes Direction Finder.) These may arise from a failure of part of the antenna system, or because the receiver has been maladjusted or improperly aligned.

Heavy Static. (Radio Compass.) A radio compass will deflect in ordinary heavy static and the static course laid out will be towards the center of the electrical disturbance.

Miscellaneous Errors. (Radio Compass.) Errors such as those due to heavy rain static, where the compass ceases to indicate, are obvious, since a change in heading produces no visual change in indication. Shielded loops minimize rain static.

Summary

Radio bearings have now reached the stage where the up-to-date navigator will use them without hesitation to supplement his dead reckoning and celestial navigation, and in time of fog or thick weather will depend upon them almost exclusively, although the cautious Captain will still insist on checking radio positions by soundings. With the combination of the two methods, there is no longer need for anchoring or standing off and on until a fog lifts—a port may be made quite as accurately and safely as far as navigational hazards are concerned as in the best visibility. Ships are the only drawback remaining—and there is now no excuse for two ships in radio communication ever colliding if one of them has a radio direction finder.

The Sperry Automatic Direction Finder is one of a type of direction finder which has been developed specifically for aircraft use, where rapidity in taking bearings is vital. This type of direction finder in which bearings are made available continuously and automatically throughout 360 degrees, has not yet, as far as is known, been applied to marine navigation. However, with this type of direction finder rapidly coming into general use for aircraft navigation, it is quite likely that it may soon receive attention for marine navigation.

Once determined, radio bearings are handled exactly as any other position lines. Remember that radio bearings may be converted to Mercator bearings graphically as described in the earlier lesson on charts. Finally, anyone planning to use radio as an aid to navigation should without fail study H.O. 205 (338 pp.), and H.O. 206 (274 pp.), since there are a great many essential details in these Government publications which obviously cannot be included here.

Observations for distance off are not restricted to vessels with direction finders, but may be made by any vessel having a radio receiver capable of receiving in the band 285 to 315 kilocycles within which radiobeacons are operated. A loud speaker is desirable although not necessary.

Warning Of Fog

Hearing the groups of short (1-sec.) and long (5-sec.) dashes of the radiobeacon, at stations where the radiobeacon and sound signals are synchronized for distance finding, is an indication that there is fog in the vicinity of the station and that the sound signal is operating.

Radiotelephones

The radiotelephone is unquestionably one of the most important pieces of safety equipment a boat can carry. It makes possible a means of communication with telephone facilities ashore, the Coast Guard, and other boats similarly equipped. With it you can call for help, and any boat equipped with a radio direction finder can easily locate you. Furthermore, it enables the yachtsman to keep in touch with sources of weather information, marine information broadcasts dealing with changes in aids to navigation, reports of obstructions to navigation, and advisory storm warnings.

Get Your Licenses

For the ship station—as soon as you have your set, apply to the Federal Communications Commission, Washington 25, D. C·, for a license. Use Form 501 A. Operate your set only when you have a valid station license. Keep your license posted on your boat.

For the operator—apply to the local office of the Federal Communications Commission for a Restricted Radiotelephone Operator

Permit. Use Form 753. Operate your set only when you have a valid permit with you, or someone else aboard has one.

Steps To Follow In Making A Call

Intershiþ calls.—Listen to make sure 2182 kc is not busy. If it is free, put your transmitter on the air and say—

"(Station called) This is (call sign and name of your vessel) (Station called) This is (call sign and name of your vessel) (Station called) This is (call sign and name of your vessel)
Over."

Listen for a reply. If no contact is made, repeat after a short interval. After establishing contact, switch to the agreed upon inter-ship channel. After conversation is completed say—

"This is (call sign and name of your vessel) signing off."

Ship to shore calls.—Listen to make sure the working channel you wish to use is not busy. If it is free put your transmitter on the air and say—

"This is (call sign and name of your vessel) calling the (coast station desired) Marine Operator."

Listen for a reply. If no contact is made, repeat after a short interval.

When the Marine Operator answers say—

"This is (call sign and name of your vessel) calling (telephone number desired)."

After conversation is completed say—

"This is (call sign and name of your vessel) signing off."

Steps to Follow in Receiving a Call

Intershiþ calls.—When you hear the name of your vessel called on 2182 kc put your transmitter on the air and say—
"This is (call sign and name of your vessel)."

Switch to the agreed upon intership channel. After conversation is completed say—

"This is (call sign and name of your vessel) signing off."

Shore to ship calls.—When you hear the name of your vessel called, or if the bell associated with your selective signaling device rings, put your transmitter on the air and say—

"This is (call sign and name of your vessel)."

After conversation is completed say—

"This is (call sign and name of your vessel) signing off." The Distress Call and Message

In making a distress call be sure to state your boat's name, where you are, what is wrong and what help you need.

Example of distress message:
 
"MAYDAY MAYDAY MAYDAY this is WZ-6789 the yacht Blue Duck

MAYDAY MAYDAY MAYDAY this is WZ-6789 the yacht Blue Duck

MAYDAY MAYDAY MAYDAY this is WZ-6789 the yacht Blue Duck

133 degrees true 12 miles off Montauk Point struck submerged object taking water fast engine disabled estimate cannot stay afloat more than one hour."

In acknowledging a distress call be sure to state your boat's name, where you are and estimated time of arrival together with your course and speed to the scene.

Rules To Remember

Your radio can mean your safe arrival; use it with respect. Here are ten important points of proper usage recommended by the Radio Technical Commission for Marine Services, Washington, D. C.

On priority calls be sure to give name and position of your vessel. Code words in emergency situations are as follows:
DISTRESS—Mayday, Mayday, Mayday.

URGENT MESSAGE CONCERNING SAFETY OF VESSEL OR CREW―Pan, Pan, Pan.

SAFETY OR WEATHER INFORMATION—Security, Security, Security.

1.MAINTAIN YOUR WATCH—Listen to 2182 kc when not in communication with another station. (Rule 8.223)

2.LISTEN BEFORE YOU TALK—Avoid interference with calls in progress. (Rule 8.181)

3. IDENTIFY YOUR VESSEL—Give your call sign and vessel's name at beginning and end of each communication. (Rule 8.364)

4. MAKE CALLS CORRECTLY—Call other vessels on 2182 kc then switch to íntership channel. (Rule 8.366)—Call Commercial Shore stations on an appropriate working channel. (Rule 8.366)

5. USE CHANNELS PROPERLY—2 182 kc for emergencies and brief calls and replies. (Rule 8.353)—Intership for safety, navigation or operational and business needs of vessels. (Rule 8.358)

6. WATCH YOUR LANGUAGE—Use of profane or obscene language is a criminal offense.

7. BE BRIEF ALL THE TIME—Limit calls to 30 seconds; conversations to 5 minutes. (Rule 8.366)

8. KEEP AN ACCURATE LOG—Enter all transmissions made and distress calls heard. (Rule 8.368)

9. HAVE DOCUMENTS HANDY—Ship Station license; Operator license or permit; Part 8 of the FCC Rules; Log Book. (Rule 8.367)

10. HAVE EQUIPMENT CHECKED—Periodic checks insure safety and good operation.

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