Patent GB-592491-A (GB)
Title: Inductance coils for precision radio apparatus
IPC: H04B1/38
Filed: 1944-02-10
Abstract: 592,491. Inductance coils. THOMSON, A. Feb. 10, 1944, No. 2515. Convention date, Dec. 8, 1942. [Class 38 (ii)] An inductance coil for precision radio apparatus comprises an insulating plate, a cylindrical coil former integrally bonded to the plate, and substantially co-terminous endwise with the plate and having its axis disposed in parallelism therewith, the plate carrying terminal blocks directly engaged by the terminal points for the coil ends in the neighbourhood of the plate. The invention is described in its application to the transmitter or receiver of Specification 592,509, [Group XL], employing antenna circuit, mixer circuit and detector circuit, the tuning-coil/condenser assemblies of which are provided with permeability-tuned, longitudinally-sliding cores 12, 12a, adapted to give straight-line frequency relation with uniform dial movement, the dial mechanism being preferably that described in Specification 582,136 and its description being reproduced in the Abridgment of Specification 592,509, [Group XL]. It also incorporates some of the improvements of Specification 582,336. The cores 12, 12a are all slidably mounted on a common ceramic rod 111 with suitable ceramic spacers and bearing members and a spring ring 122b, Fig. 5a. One end has a circumferential groove 123 detachably engaging a yoke 89 on a bellows 87, whereas a sleeve 111a on the other end is rigidly secured, Fig. 6 (not shown), to a further bellows 114 operable by a thrust-rod 115 so as to have a limited sliding movement for tuning purposes. The tuning units, Figs. 14, 15, comprise a hollow ceramic form 173 having a groove 176 receiving tongues 171 on, so as to be cemented to, a ceramic plate 166. A spiral groove 174 receives two complete turns of sterling silver or other semi-elastic ribbonconductor 175 fitted into the groove by heating and shrinking as in Specification 592,512, and secured by the rough projections of the form piercing the ribbon. The ends of the latter are soldered to tongues 179 of the same width as the groove 174, formed on terminal blocks 180, 189, the lower faces of which are shaped and soldered to coatings 185, 187 on an insulating tube 186 so as to form a condenser with an internal sleeve coating 188. A similar tongue and block 190 provides the intermediate tapping. The slug 15 is secured by screws 177 in slots 168 in the plate 166. In Fig. 20, three single turns are provided on a plain cylinder and joined at 200, 201, the tongues 179, 190 being soldered where shown. The core is introduced from the right. Fig. 23 shows a two-turn coil in a cylinder grooved at 205 which is completely filled by connector 204 so as to lock the inner ends of the turns 194, 196. The tap is taken at 190a from the connector 204. The turn 196 is of smaller diameter, the floor of groove 205 being correspondingly sloped. In another form, Fig. 25 (not shown), the ends of the turns 194, 196 are shouldered so as to extend sideways into the groove 205 for clamping purposes. The blocks 180, 189 may alternatively be shaped so as to support a plate condenser having a sheet-mica dielectric, Figs. 26-28 (not shown). Examples of coil. dimensions are given. In order to concentrate all the inductance and capacity in the oscillator itself, and therefore eliminate wiring, the terminals on the socket-plate 228 of valve VT3, which plate is as described in Specification 560,779, [Group XXXVI], are pressed by an earthed spring plate 229, Fig. 32, so that they engage the terminals 182 of the oscillator either directly or through the grid-condenser 47 which is constructed to admit of this. The resistors 49, 57 are capacity-free and directly connected to these terminals and to the plates of their appropriate byepass condensers, as 59, the bottom of which is directly connected to wire-wound resistor 58 embedded in block 95a. The cathode and one side of the heater are directly earthed by plate 231, whereas the other side of the heater is connected through a similar, but insulated plate 23, forming a byepass condenser, to its resistor embedded in block 95a, the arrangement being described in Specification 592,510, [Group XL]. The oscillator condenser 60 is shunted by a further condenser 61 of about 1 per cent of its capacity. When assembled for the first heat-run, which is carried out to mechanically stabilize the tuning unit, this condenser 61 is chosen of as nearly as possible zero temperature-coefficient of dielectric constant. A second heat-run is then carried out and the change of frequency of the assembly over the entire temperature-range, say ambient to 180 F., is noted; the condenser 61 is then replaced by a similar one having a known temperature-coefficient-such as will compensate for the frequency change in the assembly. This process is the subject of Specification 592,513, [Group XL]. The core 12a is of as large a diameter as possible for the size of form, so as to yield S.L.F. tuning over the given range of frequencies using a coil of the kind described. The Specification discusses in detail the effects of the different coils and cores on S.L.F. tuning. The effect of moving the slug 15 is to change the slope of the tuning curve, whether the slug is moved bodily as in Fig. 17 or is in the form of a pivoted arm, Fig. 36 (not shown). To line up the receiver, the mixer tube VT2 is used as a detector of signals of 122 M.C. injected into the antenna circuit, plates 96, 97 are loosened and assemblies 9, 24 of Fig. 1 are slid until proper tuning-in is obtained. These assemblies are then locked by means of the plates 96, 97 and the mixer VT2 used as a proper mixer, and the oscillator lined up at 5.2 M.C. lower than the signal. In this process, the dial is set at 135 M.C. with the core 12a fully withdrawn, and a beat-frequency oscillator is associated with the receiver I.F., whereby, when the assembly is slowly moved, zero beat-frequency is obtained when the assembly is properly located. The process is repeated for 110 M.C. signal and dial setting, and the slug 15 adjusted until proper tuning is obtained. If necessary, a second application of 135 M.C. may be made to get closer correspondence.