Patent GB-819694-A (GB)
Title: Improvements in or relating to ultra-high frequency radio receivers
IPC: H03D9/06
Filed: 1957-09-24
Abstract: 819,694. Frequency-changing circuits. MARIE, G. R. P. Sept. 24, 1957 [Oct. 22. 1956], No. 29954/57. Class 40 (6). [Also in Group XL (b)] A frequency changer for a radio receiver comprises a resonant cavity having at least a part of a wall maintained at such a temperature that it is superconductive, two input frequencies being applied to the cavity and a steady magnetic field being applied at right angles to the wall so that electrons are caused to carry out a circular motion at the difference frequency. Fig. 1 shows a " Magic T " arrangement formed by depositing a conductive layer of molecular thickness on a solid or hollow body of dielectric material. The co-linear arms 1 and 2 are mounted between the poles of a permanent magnet 10 and the whole is immersed in a Dewar vessel 22 so that it is maintained at a temperature such that the walls of the magic T are superconductive. The two input signals are applied to guides 11 and 12 respectively and the co-linear arms are resonant at a frequency between these two signals. The arrangement is such that the electrons in the end walls 13, 14 carry out a resonant circular motion at the difference frequency and so induce a signal in coils 16, 17 coupled to the tuned input circuit of an intermediate frequency amplifier. The conductive walls of the resonant cavities are divided at 23 so that currents at difference frequency do not circulate around the cavities. Preferably the two input signals are of equal level so-that the power loss and thus the heating is reduced to a minimum. In Fig. 6 a single octagonal-cavity resonator is used consisting of a block of insulating material having a conductive coating of molecular thickness. The two signals are introduced respectively through guides 58 and 59 coupled to guides 25 and 26 consisting of dielectric material having a molecular thickness coating. The guides are arranged at the cavity at right angles so as to feed energy into the cavity without introducing coupling between the guides, A magnetic field substantially perpendicular to the sides of the cavity is produced by a ring magnet 53 having four poles successively of alternate polarity, the pole pieces (such as 54, 56) being located inside a Dewar vessel 50 together with the cavity resonator so that superconductivity is produced in the walls of the cavity. Two pairs of dielectric rods at right angles 33 and 35 and 34, 36 are axially adjustable in holes in the cavity to tune it to the two input frequencies. The shaded portion of the conductive coating is removed to prevent circulating currents in the inner part of the upper surface of the cavity and to enable an output signal to be derived from a quarterwave resonant line 61, 62 connected to opposite sides of a gap 41 in the outer part of the upper coating. This resonant line consists of a thin. coating on dielectric rods and is coupled to a push-pull. intermediate-frequency amplifier 63 64. In alternative arrangements (Figs. 2 and 3, not shown) square and circular cavities are used. the waveguides being coupled to opposite sides of the cavity with their longer transverse dimensions at right angles. In addition, the coating on the outer wall is divided so as to prevent circulating currents in the wall, the divisions forming series inductance and capacitance elements broadly resonant over the range of input frequencies.