Patent GB-460821-A (GB)
Title: Improvements in high frequency signalling systems
IPC: H03J1/16
Filed: 1936-04-09
Abstract: 460,821. Valve circuits. HAZELTINE CORPORATION. April 9, 1936, No. 10521. Convention date, May 7, 1935. [Classes 40 (iii) and 40 (v)] A modulated high-frequency signalling system comprises means for expanding the band width symmetrically about the carrier and a second means to expand the band unsymmetrically with respect to the carrier to select more of one sideband than the other. Fig. 1 shows two intermediate frequency amplifiers 1, 2, of a superheterodyne receiver coupled by two parallel resonant circuits 3 4, the coupling between which is partly magnetic between inductances L and partly capacitative by condenser E. The two couplings are arranged to oppose each other, the minimum coupling occurring at the desired frequency at which the network is sharply selective. The band is broadened symmetrically by increasing the inductive coupling M the resulting double-peak effect being reduced by terminating the network in a variable resistance P. Asymmetric expansion of the band about the carrier frequency is effected by adjustment of condenser E ; decrease in capacity from the minimum coupling setting will move the centre of the response curve towards the higher frequency side-band and conversely. The high resistance R1 which shunts condenser E through blocking condenser F and switch 13, may be provided to improve the response amplitude at minimum coupling position ; switch 13 is opened to disconnect R during any band expansion. Other coupling systems may be arranged to have the same features as for example in Fig. 6 where the condenser E is connected between the inductances L and earth. Fig. 9 shows a complete superheterodyne receiver having a unitary mechanical control system of tuning and T.F. band expansion, both symmetric and asymmetric. The radio frequency tuning networks 42, 51 and the local oscillator tuning control 58 are unicontrolled by shaft 83 through a pulley system from the control knob 71 having two degrees of freedom. The inductive couplings between inductances L of the I.F. networks 60, 62, together with the variable resistances P, are controlled by the shaft 112, the switches 120, 121 being closed when the sliders on P are in their extreme right-hand position ; this control is the symmetric band expander. The asymmetric expanding reactances E, together with the switches 117, 118 controlling shunt resistances R, are conjointly operated by the shaft 91. The shaft 70 of the control knob 71 is axially slidable in the mounting frame 78 ; in its extreme left-hand position the transverse pin 72 engages the serrated collar 73, whereby rotation of 71 tunes the high frequency circuits; in the extreme right-hand position the pin engages the serrated collar 77 which drives through gearing 86, 87 the shaft 88 and thence through bevel gears 89, 90, the shaft 91 to vary the condensers E. The axial sliding movement of the shaft 70 between its limiting positions is utilised, at will, and under control of the knob 109, to vary inductive couplings L. To this end a flanged collar 102 engages a slot 103 in a sleeve member 104 which transmits the drive to the shaft 112. The sleeve 104 is laterally displaceable on the shaft 106 through a pin and slot 105 to effect engagement or disengagement with the flange 102 ; this displacement is effected by a cam 107 controlled by the knob 109. Since it is necessary that, during tuning or variation of inductive couplings L, the condensers E should always be at their mid-setting, the shaft 88 is automatically adjusted to this setting when the knob 71 is axially displaced to the left. This centring device comprises a sleeve 94 sliding on a shaft 95 by means of a flanged collar 92 on the shaft 70, engaging slot 93. The sleeve 94 is provided with a wire loop 98, Fig. 10, which engages a transverse pin 99 on shaft 88 so that movement of the sleeve to the left rotates shaft 88 until the pin enters the narrows of the loop 98. Figs. 12 and 13 show a modification, of the arrangement of Fig. 9. The tuning coridensers 130 are operated by a shaft 132 through pulleys 133, 135, such operation being only possible when the shaft 136 operating the condensers E is set for maximum intermediate frequency selectivity. This shaft 136 is axially displaceable without rotation by means of a sliding coupling 146 to shaft 147, and is rotatable through 180‹ to adjust the condensers E only in the position shown in Fig. 12, i.e. when fully pushed in to the right. In this position a transverse pin 137 Fig. 13, engages a ball 138 in an arm 139 pivoted about 140 and carrying two guide pulleys 143 which take up the slack in the pulley belt and permit tuning by rotation of shaft 132. For double sideband expansion, variation of couplings L and control of switches 166, 167 is effected by axial movement of shaft 159. The pin 137 of shaft 136 must be brought to the position shown in Fig. 13 for this adjustment, whereby the pin is aligned with a space between blocks 151 and the shaft 136 may then be axially displaced. The pin 137 in this position is engaged in a transverse slot in the block 154 to which shaft 159 is secured ; displacement of 136 thus produces corresponding movement of shaft 159 to widen the band symmetrically.