US2205359A - Superheterodyne receiver - Google Patents

Description

June 18, 1940 A. scHLElMANN JENSEN 2,205,359

SUPERHETERODYNE RECEIVER Filed June 24, 1938 l M INVEN-rocfe Patented June 18, 1940 UNITED STATES SUPERHETERODYNE RECEIVER Arne Schleimann Jensen, Emporium, Pa., as-

signor to Hygradc Sylvania Corporation, Salem, `Mass., a corporation of Massachusetts Application June 24, 1938, Seriali No. 215,538

1 Claim.

This invention relates to frequency converters and more especially to frequency conversion methods and apparatus for use in superheterodyne wave signaling systems and the like.

In the usual form of superheterodyne receiver, the intermediate frequency is fixed by the frequency dierence between the received signal frequency and the frequency of a local source of oscillations. Since the intermediate frequency is usually constant over the various frequency bands of the receiver, the difference between the received signal frequency and the oscillator frequency expressed in terms of per cent of signal frequency, decreases as the signal frequency in creases.

For example, assuming a received signal frequency of 3000 kc./sec. and assuming the local oscillator frequency is chosen from the lower side of the signal frequency e. g. 2550 kc., then the frequency difference 450 kc./sec. is 15% of the signal frequency. Y If the signal frequency is of a higher order, e. g. 30,000 kc./sec., then the local oscillator frequency would be 29,550 kc.,

and the frequency difference (45o ke.) would be only 1.5% of the signal frequency. It is evident therefore, that the tendency for pulling and interlocking between the signal and the local oscillator 'in these usual arrangements increase with increasing signal frequency, and at ultra high frequency these tendencies give rise to serious difficulties; In fact, where an ultra high frequency superheterodyne receiver is to be a practical device, it is necessary to use a correspondingly high intermediate frequency. Not only does this seriously limit the working band of the receiver, but also introduces new diiculties e. g. in the intermediate frequency amplifier and associated equipment. Consequently, it is a principal object of the present invention tc provide methods and apparatus whereby the tendency of pulling or finterlocking between the signal frequency and the local oscillator of a superheterodyne radio receiver is reduced, while allowing the receiver to be used over a wide range of wave b-ands.

Another object is to provide methods and apparatus whereby the difference between the received signal frequency and the local oscillator frequency of a superheterodyne receiver, increases with increasing signal frequency while maintaining the intermediate frequency constant.

A further object is to provide an improved form of superhetercdyne receiver.

A feature of the invention relates to a superheterodyne circuit arrangement wherein the frequency difference between the received signalmodulated carrier and thelocal oscillator frequency can always be made higher than 50% of .the signal frequency, regardless of what signal frequency is being received.

(c1. o-2o) Another feature relates to circuit arrangements for the frequency conversion portion of a superhcterodync radio receiver, whereby the output of a local oscillator has its frequency automatically multiplied throughout the tuning range of the receiver.

A further feature relates to novel forms of tubes and circuit arrangements for use in superheterodyne receivers.

A still further feature relates to the novel organization, larrangement and relative interconnection of parts whereby there is provided a superheterodyne receiver having high translational or conversion gain over a wide range of received signal frequencies.

Other features and advantages not specifically' f Fig. la is a wave diagram to explain the funcy tioning of the system of Fig. 1. f

Figs. 2, 3, 4 and 5 represent respective modifications ofV Fig. 1. f

Referring to Fig. 1, the numeral I represents diagrammatically an electron-discharge tube having an evacuated envelope enclosingI a pair of electron-emitting cathodes 2, 3; a common grid il; and a pair of anodes 5, 5, to receive electronemission from the respective cathodes.l The cathodes may be connected either within or outside the tube by a conductor 1. 1

Connected across the cathodes and the grid is a signal input circuit comprising a high frequency coupling transformer 8, the secondary of which is tunable to the signal frequency to vbe received, by means of variable condenser 9. A

suitable grid biassing potential l0 may be interposed between the cathodes and grid. lA tuned circuit, comprising the coil H and tunable `con- 'denser l2, is connected in push-pullrelationacross the anodes 5, 5. The midpoint of coil il is returned to the cathodes through the primary winding of a suitable intermediate frequency transformer, the primary i3 of which is bypassed by a high frequency by-p-ass condenser i4. Coupled to coil H, for example by coil I5, is a local oscillator l5 preferably tunable as to frequency simultaneously with the tuning of the sig" local oscillations from source i6 are of a frey quency FL and are applied to the anodes 5 and 6, then because of the full-wave rectifying action in tube I, current in conductor I9 will consist not only of a D. C. component but also of a high frequency component as shown in the cross-lined portions of Fig. 1. The frequency of this component will be 2FL. When the received signal frequency in the form of a modulated carrier Wave is applied to transformer 8, it will control the magnitude of current flowing from the cathodes to electrodes 5 and 6 thus controlling the amplitude of the current in conductor I9. Consequently, as indicated in Fig. la, a received signal (FS) on grid 4 will in conjunction with the FL frequency from source I6, give rise to a current in conductor I9 of (ZFL-Fs). Preferably, the frequency FL will be chosen so that Fs 2FL and therefore the resulting signal will be (Fs-2F10 kc./sec. and consequently the difference between the received signal frequency and the local oscillator frequency is greater than 50% of the received signal frequency. For example, if, as assumed above, the system is to receive signal frequencies at one setting of 3000 kc./sec. and of 30,000 kc./sec. at another setting, with an intersignal frequency. At the 30,000 kc./sec. setting,

it would be 30,000-14,775 or 50.75% of the signal frequency.

In the embodiment of Fig. 2, the received signal (Fs) is applied to the tunable oscillation circuit 2l, 22, tuned to frequency Fs. This signal is applied to grids 23, 24, of respective tubes 25, 26. The second grids 21, 28, of these tubes are connected in push-pull relation to the local oscillation circuit 29, 30, which is tuned to the local oscillator frequency FL. This local frequency is generated in the well known manner by feedback action through coil 38 from the plate circuits of the respective tubes, by a feed-back coil 3I, the D. C. operating potential 32 for plates 33, 34, being applied at the midpoint of coil 30. Because of the push-pull connection of grids 21, 28, the current in cathode conductor 35 has a component of frequency to 2F1.. Likewise conductor 35 also carries component of frequency Fs-ZFL to which difference frequency primary 36 of the intermediate frequency transformer 31 is tuned by means of condenser 38. The secondary of transformer 31 is connected to a suitable intermediate frequency amplifier of known construction. The grids 23 and 24 may be biased by the resistor 39 and shunt condenser 40 in the usual manner. It will be obvious that instead of mounting the various electrode sets in separate envelopes as in Fig. 2, they may be mounted in a common envelope. Such an arrangement is shown in Fig. 3 and the parts of Fig. 3 corresponding to those of Fig. 2 are designated by the same numerals. It is believed that the manner of operation of the system of Fig. 3 will be clear from the above de-V scription of Fig. 2.

Fig. 4 is a modification of the arrangement of Fig. 2. In Fig. 4 the triode tube 4I generates the local frequency FL by means of feed- back coils 42, 43 respectively connected in the plate and 45 and the cathode 46 of tube 41 which has two separate anodes 48, 48. The signal frequency Fs is amplified in tube 41 and by reason of the pushpull connection of anodes 48, 49 with the coil 43, the local frequency Fr. is doubled to 2FL and is superimposed on the circuit containing primary winding 50 of the intermediate frequency transformer thus producing the intermediate frequency Fs-2FL.

Fig. 5 is a further modification of Fig. 2, Wherein the tube 5I is provided with a cathode 52, a first grid 53, two separate second grids 54, 55, and an anode 56 common to the grids 54, 55, to the grid 53 and to the cathode 52. Associated with the cathode to receive emission from one section only thereof, is an anode 51 and a grid 58. The elements 52, 51, 58, constitute the local oscillator for generating the frequency FL. In one particular superheterodyne receiver in which the tube and circuits of Fig. 5 were used, the incoming signal coil 59 was wound to cover the frequency band 2.46-'7 megacycles using one section 60 of a S-gang tuning condenser. A small trimmer condenser 6I was connected in the usual Way in parallel with condenser 60. The intermediate frequency transformer 52 was tuned for a frequency of 460 kc., thus the tuning range for the local oscillator circuit 63, 64, 65, could be from (2.46-0.46)/2=1.0 m. c. to (7-0.46)/2=3.27 m. c. The 'tuning capacity consists of the two sections 64, 65 of the B-gang condenser referred to above, the common operating mechanism of which is indicated by the dotted connections. The two sections 64, 65, actually form a split stator condenser and since capacities 60, 64 and 65 are all of the same value, the available tuning vcapacity for the oscillator circuit is only one half of the available tuning capacity in the signal circuit 59, 68. The usual trimmer condensers 66, 61, are connected in shunt to B4, 65.

The grid 58 of the local oscillator is directly connected to the grid 55 which in conjunction with grid 54 and cathode 52 doubles the frequency of the local oscillations. Thus, there is delivered to the primary winding of the intermediate frequency transformer 62 a frequency Fs-ZFL. The grid 53 is preferably negatively biassed to cathode 52 by the usual bias resistor 68 and shunt capacity 69.

While certain specific embodiments have been described herein, it will -be understood that variouschanges and modifications may be made therein without departing from the spirit and scope of the invention. y

What is claimed is:

A superheterodyne radio receiver including a tube containing a cathode, an anode to receive emission from one section of said cathode, a control grid adjacent said section of the cathode, a pair of auxiliary grids between said control grid and the anode, another anode adjacent a different section of the cathode, a control grid for said other anode, means to couple the second mentioned anode and the second mentioned control grid to generate a local frequency FL, means to impress said frequency in pushpull `relation across said pair of auxiliary grids, and means to impress received signal modulated carrier Waves on the first mentioned control grid whereby there exists in the anode circuit of the rst mentioned anode a current of frequency Fs-,2FL.

ARNE SCHLEIMANN JENSEN.

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