New Apparatus Marconi Attainments

Radio Record, Volume II, Issue 33, 1 March 1929, Page 8

New Apparatus Marconi Attainments

‘ W apparatus representing recent developments in wireless work is being exhibited by the Marconi Company at this year’s exhibition of the Physical Society and the Optical Society at South Kensington. In addition to wireless receivers and transmitters in their complete state the exhibit ineludes such auxiliary apparatus as a signal strength measuring set, with a wave-range of from 14 to 5000 metres, and a tuning fork and thermostat unit for maintaining constant frequency in facsimile transmission. One of the most notable features in eounection with the use of maritime wireless is the remarkable extension of the use of direction finding apparatus on ships of practically all types. For some years after the introduction of the marine direction finder the use of this instrument’ was confined almost entirely to the large passenger liners and a few yachts. It is now to be found in béth large and small cargo vessels, tug boats, cross-channel vessels, pilot étaft, whalers, salvage steamers, and %s also being largely made use of in trawlers. Since 1914, when the direction finder was first introduced commercially as an aid to navigation, on the 8.S. Royal George on her voyage from Bristol to Montreal, the Marconi Company alone has fitted upwards of §40 mercantile vessels with this instrument, and it is noteworthy that, more than half of this number has been fitted during the last 18 months. The interesting feature of this increase is the growing percentage of cargo vessels making use of this aid to navigation.

The latest type of direction finder is used in conjunction with a fixed frame aerial and possesses @ number of important features, the chief of which are the screened valve amplifier, which is highly efficient and stable in operation, and a radio geniometer provided with two scales, one for reading bearings relative to the ship’s head and the other for reading true bearings. The instrument covers 2 Wave-range of from 400 to 1100 metres, and the circuits are easily and quickly tuned to ar ~ wavelength within this range for the reception cf spark, interrupted continuous wave and telephone signals. There is also shown a new receiver, developed for naval and military purposes with a maximum to minimum wave-range ratio of 2.5 : 1, the set being highly efficient over this range of wavelengths. Another piece of apparatus particularly suited to shipping is the Marconi Auto-Alarm. This responds only to an alarm signal consisting of 4-second dashes with one second intervals, the alarm bells ringing on the receipt of the third consecutive dash. Working demonstrations of this apparatus are given. The extent to which this apparatus is used by British shipping is shown by the fact that 929 sets have already been installed. An instrument of great utility for authorities allocating transmitting licenses, for research workers in wireless phenomena, and for those respousible for commercial wireless stations, is this signal strength measuring set, which has been produced by the research laboratories of the Marconi Company. A frame aerial for the reception of the desired signals is mounted on a coupling unit which also contains a means of attenuating the signals produced by a local oscillator. The local oscillator is capable of being tuned from 14 to 500 metres, and is coupled to the frame and to a receiver. By means of the attenuator unit the signal strength of the local oscillator can be measured and can be made equal to the received signal. The signals can be equalised by ear, or, in the case of rapidly varying signals, such as occur in the short wave-band, the receiver output can be calibrated on a recording «levice. The local oscillator output is adjusted to be of exactly the same frequency as the signals to be measured and the current is measured by 2 thermomilliammeter. The receiver is a frame and the set will therefore measure primarily the magnetic field in the wave at the point considered, and the audio intensity of the signal produced is measured by comparison with the known signal strength of the local oscillator. The attenuator and coupling unit, the local oscillation generator, and the batter box, are each contained in a heavy metallic shielding case, which completely screens these units from external interference.