Improvements in detector circuit arrangements for use at high radio frequencies

585,473. Valve receiving circuits. STANDARD TELEPHONES & CABLES, Ltd., and WILLOUGHBY, E. O. Aug. 1, 1944, No. 14700. [Class 40 (v)] In a radio distance determining arrangement depending on the frequency sweep principle, a leaky grid detector for determining the frequency difference between the outgoing and incoming signal, has its grid effectively earthed at high frequencies and the two signals rare fed onto the cathode circuit ; thereby ensuring a low input impedance at high frequencies, :at which the anode circuit comprises a low impedance byepass circuit, while presenting a high impedance at the detector signal frequency. The detector valve 1, Fig. 1, which is of the grid disc type as disclosed in Specifications 585,448, 585,449, 585,450, 585,452 and 585,454 is mounted in a screening case ; whose parts 8, 9 of different diameters are connected by the apertured disc 10 'whose capacity 11 with the grid disc 5 effectively earths the grid at signal frequencies. The two frequencies whose difference is required are fed to the cathode from the coaxial conductor 17 to the lead 15 and the casing 8 which forms with conductor 14 a resonant cavity. Grid leak resistance 18 is connected to earth or to a suitable source of AVC. Condensers 21, 23 and capacitative transmission line 25 together with chokes 22, 24, 26 form a low-pass filter permitting transmission of the detected frequency only. In cases where the detected frequency is of the same order as the signal frequency and consequently capacity 11 must be made smaller the.grid may be connected to earth by means of a series circuit resonant at the signal frequency. In an alternative arrangement, Fig. 2, both transmitted and reflected waves are received on a half-wave dipole 30, coupled by condenser plates 32, 33 separated by mica sheet 31, to a short transmission line stub to give it a band pass characteristic and to the quarter wave transmission line leading to the cathode of the valve. The filament lead within tube 14 is decoupled by the capacity 16, 12.