3^4 



NATURE 



[May 19, 192 1 



that, as an alternative, two or more direction- 

 finding stations of a group covering a certain area 

 may be equipped with receiving gear only, and 

 an ordinary separate transmitting and receiving 

 station may undertake the controlling duty. A 

 station may be self-contained. In such case the 

 aerials for the direction-finding receiver and for 

 the transmitter must be spaced a short distance 

 apart, whilst the receiving and the transmitting 

 apparatus must be housed in separate buildings, 

 the whole of the receiving being done on the 

 direction-finding receiving apparatus, and the 

 transmitting apparatus being operated electrically 

 from the direction-finding room. 



A ship equipped with directional wireless ap- 

 paratus can obtain bearings from any known 

 ordinary wireless telegraphy shore station ; but 

 it is preferable that certain of these stations should 

 be detailed to transmit, simultaneously or suc- 



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Fig. 2. — Simple circuit for aperiod ic aerial and spark reception aboard ship. The beam aerial is 

 rigged in the thwartship line so that it receives no induced signals from the ship. Tlie funnel, 

 or fore-and-aft, aerial receives signals direct flus induced signals from the sliip. If the two 

 aerials are adjusted to an equal sensitivity, they will always produce a resultant field in the 

 direction-finding transformer in the same line as the incoming wireless wave, and the bearings 

 obtained will be correct. 



cessively, signals on given wave-lengths at 

 definite times during each hour. This is known 

 as the Beacon Station method. Only vessels 

 fitted with direction-finding apparatus are able to 

 use it. The apparatus comprises a twin direction- 

 finding aerial .system consisting of either 

 suspended fixed wires or large rigid frames, to- 

 gether with wireless direction-finder, tuning ap- 

 paratus, and receiving and amplifying gear, with 

 batteries and charging plant. A cabinet for the 

 apparatus and operator, and telephone or buzzer 

 communication with the ship's steering position, 

 are also necessary. Such an installation costs 

 about 300Z., apart from the expense of fit- 

 ting it. Any number of ships can obtain 

 bearings, or fix their position, at the same time 

 from the same station by this method, and are 

 able to do that over much longer ranges than is 

 the case with the method first described. As, 

 NO. 2690, VOL. 107] 



hovi^ever, ships using their own direction-finding 

 sets are responsible for the accuracy of the bear- 

 ings obtained by them, their staffs require some 

 technical skill in the work, and it is necessary that 

 the instruments should be calibrated and checked 

 occasionally. 



In the third method a rotating directional 

 wireless beam having a fixed angular velo- 

 city is transmitted by a specially fitted fixed 

 transmitting station. The rotating beam has a 

 sharply defined zero direction which passes 

 through North and South at given times. Know- 

 ing the angular velocity of the beam, and by 

 observing the time interval between the given 

 times at which the zero passes through North 

 and South and the time at which the zero signals 

 are received in the ship, the bearing of the station 

 can be determined. 



In order to ensure that the watches in the trans- 

 mitting station and the receiving 

 ship are synchronised, the sta- 

 tion transmits a timing signal 

 before commencing the rotating 

 beam. To use this method, a 

 ship must carry on her bridge a 

 special watch, the face of which 

 is marked in degrees, the scale 

 corresponding to the angular 

 velocity of the rotating beam. 

 If this watch is started at the 

 moment indicated by the timing 

 signal, the bearing in degrees of 

 the ship from the station can be 

 noted from the watch at the 

 moment when zero signals are 

 received, and this bearing can be 

 checked with subsequent zeros. 

 During the war Germany had 

 three stations working by this 

 method, but Great Britain has 

 none. 



Aboard ship the simplest form 

 of direction-finding apparatus is 

 a single-loop aerial rotated round 

 its vertical axis through a hori- 

 zontal scale. To increase the current through the 

 loop, it is usual to tune the loop with a condenser to 

 the wave-lengths required to be received, and 

 instead of a single loop a frame fitted with a multi- 

 turn loop may be used. In the Bellini-Tosi system, 

 in place of a rotating loop aerial two fixed loop 

 aerials are employed, these being connected to 

 an instrument known as the radiogoniometer, or 

 direction-finder transformer. Inside the latter is 

 a small revolving coil attached to a pointer 

 moving over a scale by which the direction of the 

 signals can be determined. Since, however, the 

 receptive powers of a comparatively small loop 

 aerial, such as can be employed in direction-find- 

 ing aboard ship, are very much inferior to those 

 of the ordinary type of ship or shore station 

 earthed aerial, a signal-amplifying apparatus em- 

 ploying several vacuum valves is an essential 

 feature of the direction-finding receiver. 



