GB520606A - Improvements in or relating to radio direction finders - Google Patents

Abstract

520,606. Directive wireless signalling. STANDARD TELEPHONES & CABLES, Ltd. (Materiel Telephonique Soc. Anon.) Nov. 15, 1938, No. 33189. [Class 40 (v)] ' In order to avoid " night-error " in directionfinding, only the first or " direct-path " portion of a transmitted signal is allowed to operate the indicator, the later or " reflected " part of'the signal being prevented from getting through. The initial part of the signal is used to vary the charge on a storage condenser, the potential of which is maintained constant for the remainder of the signal and is then restored to normal. The arrangement is designed for use with the standard, as distinct from the " impulse " type of transmission and ordinary receiving aerials can be used. The signal is received on a directive aerial 31, and simultaneously on a non-directive aerial 32. The receiving circuit 11 of the frame aerial is normally blocked by a negative grid-bias, but this is released for a very short interval of time by the signal received by the non-directive aerial 32. The latter signal passes through a receiving circuit 12 and is used to trigger a gasfilled valve 47, and so discharge a condenser 51 during a period of about one five-thousandth of a second. This produces a rectangular waveform which is applied through a transformer 61 to release the bias on the amplifier 11 for that period of time, and so allow the initial part of the signal to pass through to the phones 81 at a strength which is determined by the orientation of the frame aerial 31. The part of the signal which passes through reduces the charge on the condenser 52 by a certain amount, but the residual charge remains constant during the remainder of the signal, and is only restored during the interval between two signals. Modulation potentials are applied from a source 73 and are heard at a strength proportional to the setting of the aerial 31.