Patent GB-585624-A (GB)
Title: Improvements in antenna input systems for radio receivers
IPC: H03H2/00
Filed: 1944-10-24
Abstract: 585,624. Aerial coupling arrangements. BURGESS, A. F. (Zenith Radio Corporation). Oct. 24, 1944, No. 20626. [Class 40 (v)] An aerial input system comprises a loop aerial and a separate coupling coil, predominantly inductive in a predetermined frequency band and means for tuning the circuit to a frequency in the band, a stationary coil being connected between the coupling coil and a terminal provided for attaching another aerial. A receiver, Fig. 4, for operation on the " police " short wave and broadcast bands has a loop aerial 15, a terminal 23 for attaching an extra aerial 23<1> and a short wave aerial 25. With the band-change switches 30, 31 in the " police " position, as shown, the loop aerial 15 is connected in parallel with a stationary coil 27 and a shunt resistance 28 through contacts 29, 33 of the switch 30. The short wave aerial 25 is connected to the extra aerial 231, if used, and one side of coil 28 through contacts 35, 29 of switch 30, and to earth through primary coil 34. The tuning condenser 39 is connected in parallel with secondary coupling coils 42, 45 and condenser 48 through contacts 40, 41 of switch 30 and condenser 46 is connected across coil 45 through contacts 47, 36 of the switch 31. The tuned circuit 42, 45, 39 is connected between ground and the grid of amplifying valve 20 via a condenser 50 and contacts 41, 40, 49 of switch 30. For reception on the shortwave band switches 30, 31 are moved one step in the clockwise direction, thus connecting the common point of coils 45, 42 to earth via contacts 44, 46 of the switch 31. The circuit connections of switch 30 are not altered. On both the " police " and short-wave bands the loop aerial 15, coil 27 and the extra aerial 23<1>, if used, form a capacitive aerial used in conjunction with short-wave aerial 25. For reception in the broadcast band the switches 30, 31 are moved two clockwise steps from the position shown, establishing the circuit of Fig. 6 (not shown). One end of loop aerial 15 is then connected through the condenser 50 and contacts 33, 49 of switch 30 to the grid of valve 20, and through contacts 33, 40 of switch 30 to tuning condenser 39. The other end of loop aerial 15 is connected via contacts 32, 43 of switch 31 to coupling coils 42, 45 and through coil 27 to terminal 23 and extra aerial 23<1> is used. When aerial 23<1> is not used, coil 27 is self-resonant at a frequency above the band in which coupling coils 42, 45 are predominantly inductive, thus decoupling terminal 23 from the receiver. The resonant circuit comprises loop aerial 15, coupling coils 42, 45 and tuning condenser 39. By moving switches 30, 31 another step clockwise, condenser 39 is replaced by a set of condensers in the automatic tuning mechanism 38. A loop aerial, Fig. 2, for use in the arrangement consists of a wire 15 wrapped round spacing rods 14 which engage the two side walls 10. An electrostatic shield 21 is formed by wires wound on the outside of plates 10 and connected, with the low voltage. end of the loop aerial 15, to a terminal, attached to the lower bearing member 17. A resilient ,contact 19 engages the lower bearing pin. The other end of loop aerial 15 is similarly connected to the upper bearing pin, thus enabling the aerial assembly to rotate through any number of turns.