Radio age (Jan 1927-Jan 1928)

14 RADIO AGE for January, 1927 The Magazine of the Hour When Radio Turns Navigator Radio Direction Finder Guides and Locates Vessels "T ~[~NABLE to Sive Position — last bearings taken ^•J three days ago — we're lost!" ! Thus reads the terse but dramatic message from a ship in distress. Out in the blackness of the night, pitching and tossing on waves stirred to a frenzy by the wintry gale, are fellow mariners and passengers, far off the traveled ocean lanes and all but lost save for the slender thread of radio communication. "Keep sending us test signals," flashes back our operator. "Will locate by direction finder." And so the latest wonder of marine radio and the newest aid to modern navigation is brought into play. Soon our operator is at the radio direction finder in the pilot house. A moment later he is wearing the headphones and View of radio compass loop mounted on upper deck of vessel. Rotation of the loop is controlled from inside the cabin beneath. manipulating the receiver dials. He begins turning the handwheel, which serves to swing the small loop frame on the deck above into the very teeth of the angry gale. The operator listens intently, the captain and others silently stand nearby; the swings of the hand-wheel become shorter and shorter. Here it is — the line of signals — the direction of their passage through space from the radiating point! But on which side of our ship — in what sense? Now the operator throws a switch, swings the hand-wheel again. The swings become shorter until they virtually stop. The operator now bends down as he peers through a magnifying glass, squinting an eye so as to line up the parallax lines which will give an accurate reading from the compass card below. Then he gives the reading to the pilot of the ship. A few moments later the course is changed, and the ship throbs to the command of full speed ahead in the face of a heavy sea. One hour, two hours, three hours — and our ship comes within searchlight range of the vessel in distress. A rescue is out of the question in such a rough sea, but we stand by, ready to act if absolutely necessary. The direction finder has completed well the task which radio began. JUST as the dog turns his ears in determining the direction of sounds, so does the radio direction finder turn its loop to get a bearing on a given transmitter. This ingenious radio device operates on the principle that a given signal of maximum intensity will be received with a loop so placed that its plane is pointing at the radio station which is transmuting. If, on the other hand, the plane of the loop lies at right angles to the direction of the radio transmitter, no energy is picked up and nothing can be heard in the earphones. The position at which the signal drops out, or so-called minimum, is well defined and is employed in reading the direction of the transmitting station from the compass card that forms part of the apparatus. The standard marine direction finder, as now installed on many ships, is entirely self-contained and occupies less than two square feet of floor space, in the pilot house or chart room. On the deck, above the pilot house or chart room, is the sturdy tripod frame supporting the loop which is encased in bakelite tubing with aluminum alloy fittings. The protective tubing of the loop measures 414 inches in diameter, while the loop measures 30 inches on a side. A 2 to 1 reduction gear, operating by the vertical handwheel, serves to swing the loop in all directions, even in high gales, without backlash or interference or muscular exertion. An eight-tube super-hetero (Continucd on page £1) Rotation control of the radio compass loop and the receiver used for picking up directional signals.