EQUIPMENT AT SEA.

New Zealand Herald, Volume LXVIII, Issue 20968, 3 September 1931, Page 15

EQUIPMENT AT SEA.

MODERN TRANSMITTERS. CRYSTAL CONTROL EMPLOYED. Generally there are two main transmitters on the modern transatlantic liner, states a writer in an English wireless magazine. One covers waves from 600 metres to 2500 metres and uses an input power of approximately 1£ kw. and another covers a wave-band of from 17 metres to 36.6. This may bo used for either telephony or telegraphy. When used a' telegraph transmitter considerably less power is required. Tho frequency output of the transmitter is controlled by a quartz crystal, cut to the desired frequency. This eliminates the swinging and slight alteration in wavelength radiated which is so annoying on short-waves. Both these transmitters use valve transmission, spark being practically obsolete. A third transmitter, carried for emergency uso, usually has a power input of about and in this case spark is used. The use of short waves has enabled vessels to be in constant direct communication with land throughout their voyage. This has effected a considerable reduction of the charges for a radio-tele-gram. In the receiving office are several receivers, covering the wave-bands from 12 to 25,000 metres. Usually there are two short-wave receivers which cover the 12 to 100 waves. These are usually superheterodyne and are used either on telegraph or telephone working. Other receivers cover tho normal working waves from 600 to 2500 metres. There is also a special receiver designed for use on the higher wave-lengths. Duplex working has been accomplished after considerable experimenting with receivers and screening of aerials. It is now possible to receive a station on, say, 2400 metres and be transmitting to the same station on a 2200-metre wava, although the receiving aerial is probably only about 20ft from the aerial used for transmission. Throughout the day and night the telegraph bureau is kept open for the acceptance of wireless telegrams destined for any part of the world or for any vessel at sea. The time taken for delivering a radio-telegram from a ship at sea to any point in either Great Britain or United States is only slightly in excess of that taken by an ordinary telegram handed in at any post office and destined for similar places. From beginning to end of a voyage, one receiver is kept permanently tuned to the 600 metre-wave and a loud speaker attached. This enables the operator to listen to any distress calls that may be sent out on that wave, even although he happens to be working another station at the time immediately upon receiving a distress call, all work on hand is Btopped and the operator's full time devoted to rendering assistance to the unfortunate ship. Another instrument in tho receivingroom is the wireless direction finder. This receiver enables the operator to find the vessel's position in the thickest of fogs. A radio-goniometer is incorporated in this receiver, which has a dial calibrated in degrees, 1-560. Bearings are taken of, say, two land stations whose exact position is already known, and these two bearings, when placed on the navigation chart, will be found to cross at the exact position where tho vessel was at the time. Another item, purely for the safety of life at sea, is the installation of two large motor lifeboats, with a complete wireless transmitter and receiver. The transmitter is generally about £-kw. 6park and obtains its power either from batteries or a small generator driven by a potrol engine. Direction finders are also installed in several instances.