Patent GB-402443-A (GB)
Title: Improvements in or relating to wireless direction finding systems
IPC: G01S1/02
Filed: 1932-05-26
Abstract: 402,443. Directive wireless signalling; television. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Electra House, Victoria Embankment, DOWSETT, H. M., 47, Drayton Gardens, Winchmore Hill, WALKER, L. E. Q., 98, Wymering Mansions, Maida Vale, both in London, and CADZOW, R., Ardentinny, Argyllshire. May 26, 1932, Nos. 15012 and 27717. [Class 40 (v).] A direction-finding system comprises means for transmitting a television picture identifying the transmitting station and a tone or like frequency, the receiver being provided with means for reconstituting the picture and using the tone frequency to superimpose thereon an indication giving the direction of the transmitting station. In one embodiment, a rotating beam aerial B Fig. 1, carries a drum A with a compass scale thereon moving behind a window W carrying letters identifying the transmitting station, signals corresponding to a picture of said window and produced by a Nipkow disc D and photoelectric cell E being transmitted from an omni-directional aerial F on a carrier derived from a source CD. The aerial F also transmits synchronising impulses while the rotating aerial B transmits a carrier derived from the source CD and modulated by a tone frequency derived from the motor G driving the disc D and amplified in valves V1, V2, the motor G being controlled by a fork H. The tone frequency is such as would produce a single black bar across the received television picture if it were superposed on the television signals. To prevent said bar extending right across the received picture the amplifier V1, V2 is controlled by a photocell K which is illuminated only during the transmission of half of one complete picture, the light being required to pass through the holes of the disc D half of which are screened by a mask 1. At the receiver the television image is reconstituted and is of the form shown in Fig, 2 and shows the scale markings, 1, of the drum A at the transmitter, a pointer P, the station identifying letters and a space SL in which the black bar above referred to and due to the signals from aerial B appear when said aerial is pointing towards the receiving station. The pointer P at this instant indicates on the scale I, the direction of the transmitter. In a modification, the television apparatus may be replaced by a record of the required signals on a telegraphone tape or other medium, Fig. 3 (not shown). In another embodiment a picture identifying the transmitting station and a tone frequency are transmitted omni-directionally and at the receiver an omni-directional aerial system is used to reconstitute the picture and a directional aerial system for superimposing the tone frequency on the signals fed to the picture reconstituting apparatus, the picture signals and tone frequency signals being separated out at the receiver for this purpose by filters, &c. The picture then gives an indication of when the directional receiving aerial is pointing towards the transmitter. In a modification of this last method, the television signals and tone frequency are received on the directional aerial system while the synchronising signals only are received on the omni-directional system. In this case the intensity of the picture itself gives a directional indication. Synchronism may be effected by providing transmitter and receiver with independent master time period devices. Specification 400,610 is referred to in the first Provisional Specification.