Month in the Patent Office: A Selection from Important Aircraft and Aero Engine Specifications Recently Published

The height of aircraft above the earth is indicated by radiating towards the earth, from the craft, high‐frequency oscillations of varying frequency and combining the oscillations reflected from the earth with oscillations radiated directly from the craft to produce a current of beat frequency. Arranged on the aircraft is a transmitter 1 and a receiver 2, the transmitter radiating from an antenna 4 waves which travel downwards to the earth and are reflected on to an antenna 7 on the receiver. The received waves may be amplified and heterodyned with a wave received from the transmitter 1 directly, as through a circuit 8, the beat‐frequency current being supplied to headphones or other frequency‐responsive devices 11. In the transmitter 1 is an oscillation‐generating valve 14 having a tuned circuit comprising a capacity 15 and an inductance 16, a portion of which is included in the primary winding of a transformer 17. In shunt with the condenser 15 is a linear‐frequency condenser 19 the rotor of which is driven by a motor 12, so that the frequency of the oscillations generated by the valve 14 is caused to vary cyclically. These oscillations are supplied to the antenna 4 through a winding 20 on the transformer 17 and a commutator 21 insulated from the condenser rotor at 9 and having half its periphery formed of nonconducting material. A portion of the oscillations produced are supplied through a circuit 8 to the primary winding 23 of a transformer 24, which has a second primary winding connected to the receiving antenna 7, which receives waves reflected from the earth. The secondary winding of the transformer 24 is connected to a rectifying valve 25 and is tuned to the frequency of the received waves by a linear‐frequency condenser 27, the rotor of which is driven by the motor 12, so that the frequency to which the receiver is tuned is equal to and varies synchronously with the frequency of the transmitted waves produced by the oscillation generator 14. The circuit 8 may be omitted if the capacitative coupling between the antennae 4, 7 is sufficient.