US2268998A - Reducing disturbances in radio reception - Google Patents

Description

Jan. 6, 1942. z. BAY 2,268,998

REDUGING DISTURBANCES IN RADIO RECEPTION Filed Nov. 2,-- 1939 2 Sheet-sheet 1 Patented Jan. 6, 1942 curl-Inn); STATES.y PATENT* OFFICE l REDUCIN G DISTURBANCES IN RADIO RECEPTION Zoltan Bay, Ujpest, near Budapest, Hungary, assignor to Magyar Wolframlmpa Gyar Kremenezky Jnos Rszvnytrsasg, Budapest,

, Hungary, a Hungarian company Application November 2, 1939, Serial No. 362,566

In Hungary October 18, 19-38 claims. (c1. 25o- 20) elimination'of the disturbance is not obtainable I in a system of this kind owing to the fact that the interaction between the signal and the disturbances leads to the production of an interference preventing the required complete compensation-from being attained."

-In the method for the elimination of disturbances accordingv to the invention the compensation of the disturbances lis also carried out in a `lowfrequency stage, but in such a manner that the interfering component impairing the reception is not produced, so that aV complete com` pensation is obtained.

According to the invention this result is attained in that by means of the disturbances'received in the auxiliary wave band and by means ofvthe combined signal and disturbances received in the desired wave band a current. component is produced which is equal to the component disturbing vthe reception and which is used for compensating the latter.

The signal, the disturbances and th'e combined signal and ydisturbances may be expressed by the following formula in which S is the signal, a the signal amplitude, B the disturbance Vand b the disturbance amplitude:

a-l-b cos qa IV From this quantity that will be termedthe intermediate quantity, the undisturbed signal modulation a may be derived only by producing, in some suitable manner, a compensating quantity b cos qb and by subtracting this lcompensating quantity from the intermediate quantity A afl-Z)` cos qs y The :production of the compensating quantity b cos p is, however,-not possible'directly.

In order to produce this quantity it is neces-V sary to derive `from the oscillations received in the auxiliary wave band a quantity b sin 4; y V

and this quantity b sin p is to be transformedv into the quantity b cos qs, which may be done as follows. The quantity by sin and the disturb--V ance amplitude b' received in the auxiliarywave band are both raised to a square and after this the square of the former quantity is subtracted from the square ofthe latter so that a new quantity: 'f

is obtained from whiclilthe desired compensating quantity b cos may be produced by extraction of roots. If the'square rootV thus obtained is sub' tracted from the quantity IV the .undisturbed signal a will be obtained.

According to the inventionall the operations mentioned` above f are produced by electrical means, as shown by thev following examples.

In one method for the production of the quantities IV and Vv the high frequency signal oscillations, by being mixed on the homodyne principle with a locally produced identical unmodulated oscillation, are rectied in two distinct stages in such' amanner that the signal oscillations and the local oscillation are multiplicatively comb-ined with the same phase in one homodyne stage and are multiplicatively combined with a relative phase difference of 90 in the other homodyne stage, thus'producing a quantity a-l-b cos d in one stage and a `quantity b sin i in the other stage, both of. these being proportional to the intermediate quantity IV.

Another example for the production of th'e quantities IVKand V is that a cathode ray tube having two pairs of deflecting plates is employed in such a manner that one of these pairs is supplied With the desired high frequency signal ,osc illations,v and thev other pairis supplied with the unmodulated local oscillation of the same irequency and -phasewhile the yintensity of the cathode ray is vcontrolled in the rhyth'm of the signal oscillations and the cathode ray current is collected by two collecting electrodes having a relative displacement of In this case the quantity b sin qb will appear at one of the collecting points and the quantity a+b cos p will appear-to the other collecting point. These quantities are proportional tothe :intermediate quantity IV. It is to be observed that this method, as far as its working principle is concerned, is the same as the first method. For, in the cathode ray tube the homodyne rectiiication described above is likewise produced.

The squaring to be executed according to the invention may be realised by means of a diode provided with a suitable external resistance; the relation between the voltage produced by the diode current in the external resistance, and the input voltage is substantially a quadratic relation. So, if the voltage the square of which is to be produced is supplied by way of input to the diode, an output voltage may be derived from the external resistance which is substantially proportional to the square of the input voltage.

The extraction of roots according to the invention is realised for instance by means of the upper bend of the characteristic of a suitable electron discharge tube; in this bend the relation between the grid voltage and the anode current is known to be substantially quadratic. Likewise the lower bend of the characteristic of a tube of this type may be employed for the squaring according to the invention.

Further the squaring and the extraction of roots may be realised by means of a conventional cathode ray tube in which the cathode ray is brought in the shape of a line by means of electron lenses. This line shaped cathode ray is moved by means of deecting electrodes over a collecting electrode which is so out away that the relation between the voltage supplied to the deflecting electrodes and the current delivered by the collecting electrode is of substantial quadratic nature.

In the drawings some circuit arrangements are shown by way of example for realising the method for the elimination of disturbances according to the invention. Fig. 1 is a diagram of a circuit in which two homodyne stages are used; Fig. la is a diagram of an embodiment of one of the squaring stages in the circuit of Fig. 1; and Fig. 2 is a diagram of a circuit in which a cathode ray tube is employed.

The modication shown in Fig. 1 comprises an aperiodic amplifier I delivering the received oscillations represented by the Formula III. The aperiodic ampliiier has connected thereto two homodyne stages 2 and 3. The purpose of these stages may be explained as follows: A local os-cillator Il produces oscillations having the same frequency as the received oscillations represented by the Formula III. These local oscillations are supplied to the homodyne stages 2 and 3 and in these homodyne stages they are multiplicatively mixed with the received oscillations supplied from the aperiodic amplifier I. In the homodyne stage 2 ,the local oscillations and the received oscillations have the same phase, and in the homodyne stage 3 there is a relative phase displacement of 90 between the local oscillations and the received oscillations. Consequently, in stage 2 a quantity is produced which is proportional to a-I-b cos c, and in stage 3 a quantity is produced which is proportional to b sin 1). The quantity a-I-b. cos e is supplied to a stage 9 the purpose of which will be discussed later on.

The quantity b sin e is supplied to the squaring stage 'I where it is electrically squared so that a quantity b2 sin2 c is obtained. 'Ilie quantity b2 sin2 qb is supplied to va stage 8 the purpose of which will be discussed later on.

To the aperiodic amplifier I there is further connected a disturbance and amplier 5. From the received oscillations delivered by the aperiodic amplifier I and represented by the Formula III the -disturbance receiver and ampliiier selects the disturbance represented by the Formula II. This disturbance is supplied to the stage 6 where it is electrically squared with the result that a quantity proportional to b2 is supplied by the stage 6 to the following stage 8. In stage 8 the difference between the quantity b2 supplied by the lstage 6 and the quantity b2 sin2 qs supplied by the stage 'I is produced and the square root of this difference is formed so that the quantity bv cos c is obtained. In stage 9 this quantity is subtracted from the quantity a-I-b cos 4 supplied by the stage 2 and finally the quantity a thus obtained, that is the undisturbed modulation, is amplied by the nal amplifier I0 and supplied to a loud speaker or other suitable reproducing device II. Between the local oscillator 4 and the aperiodic ampliiier I a `receiving apparatus 4a is connected for synchronising purposes, said apparatus rbeing adapted to supply the required synchronising voltage to the local oscillator 4, particularly at low signal amplitudes. The squaring stages 6 and 'I may be of the type shown in Fig. 1a, wherein 22 are the ini put terminals of one of the squaring stages, 23 a diode, 24 an external resistance for the diode, and 25 the outputr terminals of the stage.

The method and arrangement according to the invention may be advantageously 4combined with means limiting or suppressing the amplitude on the occurrence of disturbances; Afor when disturbances occur the increased amplitude causes the effect of the compensation to be substantially reduced owing to the distortion produced. For this purpose amplitude limiters may be provided in the circuit of Fig. 1 at the input of the individual stages.

The modification shown in Fig. 2 is different from that of Fig, 1 in that the quantity a-I-b cos p as well as the quantity b sin qs are produced by means of a cathode ray tube having two pairs of defiecting plates. The pair I5, I6 is supplied with the received signal voltage represented by the Formula III, and the pair I1, I8 is supplied with an unmodulated oscillation produced by the local oscillator I4 and having a frequency equal to that of the received high frequency oscillation, but being out of phase therewith. Under these conditions the combined influence of the pair of deiiecting plates I5, I6 and the pair of deiiecting plates I'I, I8 will cause the cathode ray to describe a circle on the screen of the tube. If under these conditions a collecting electrode I9 is provided at a point of the circle described by the cathode ray the current owing to this collecting electrode will be proportional to sin t in view of the fact that the cathode ray revolves and the collecting electrode remains stationary. The current to another collecting electrode 20 also provided on the circle described by the cathode ray but being displaced 90 with respect to the collecting electrode I9 will be 90 out of phase with the current to the electrode I9, that is, will be proportional to sin (MH-90). If now the cathode ray is not maintained constant but is modulated by mea'ns of the Wehnelt cylinder I3 in the rhythm of the received high frequency oscillations represented by the Formula III, as indicated in Fig. 2, the currents flowing to the collecting electrodes I9 and 20 will not be proportional to sin ...t and sin (wt-+90), as stated above, but will be proportional to the products of these quantities with the quantity III, that is to b sin qi and a-l-b cos qb. Thus, by means of the cathode ray tube of Fig. 2 with collecting electrodes I9 and 20 the same result will be obtained as by means of the homodyne stages 2 and 3 of Fig. l. The other parts of the circuit of Fig. 2 are the same as those of Fig, 1, which is indicated by corresponding reference characters b1 and b2 are sources of current.

I claim:

l. In a method of reducing disturbances in the low frequency stage of a radio receiver, the steps which comprise receiving, in a desired wave band, oscillations which include transmitted signals and disturbances, simultaneously receiving said disturbances in an auxiliary band not occupied by a transmitter operating at the time, producing of the disturbances received in both said bands a quantity b cos qs which is equal to a quantity representing the disturbances and wherein b is the amplitude of the disturbances and is the phase angle between the signal to be received and the disturbance of the same frequency, and using said quantity for compensating the disturbances.

2. A method according to claim l wherein the effect of disturbances of great amplitude is reduced by reducing the amplitude for the time of the disturbance.

3. In a method of reducing disturbances in the low frequency stage of a radio receiver, the steps which comprise receiving in a desired wave band,

sin2 (p, squaring the amplitude of the disturbances received in the auxiliary band so as to form the quantity b2, subtracting saidv quantity b2 sin2 c from the quantity b2, forming the square root of the quantity resulting from said subtraction so as to obtain a compensating quantity b cos qb, producing of the oscillations received in the desired wave band the quantity a-l-b cos wherein a is the signal amplitude, and subtracting said compensating quantity from said quan- 4. In a method of reducing disturbances in the low frequency stage of a radio receiver, the steps which comprise mixing high frequency signal oscillations, on the homodyne principle, with a local oscillation of equal frequency and in equal phase so as to produce a quantity a-l-b cos 4 wherein a is the signal amplitude, b the disturbance amplitude and the phase angle between the signal to be received and the disturbance of the same frequency, simultaneously mixlow frequency stage of a radio receiver with the aid of a cathode ray tuber having two pairs of deflecting plates and two collecting' electrodes with a spatial displacement of 90, the steps which consist in the supplying of high frequency signal oscillations to the one pair of deecting plates, simultaneously supplying a local unmodulated oscillation of the same frequency and.

phase to the other pair of deflecting plates, while modulating the intensity 'of the cathode ray in i the rhythm of the signal oscillations, and colylecting the currents from each of the collecting electrodes, thereby to produce two quantities a-l-b cos c and b sin o respectively wherein a is the signal amplitude, b the disturbance amplitude and c the phase angle 'between the signal to be received and the disturbance of the same frequency, preparatory to forming a third quantity b cos c and subtracting the last-mentioned quantity from the quantity a-l-b cos c'.

6. In a system for reducing disturbances in the low frequency stage of a radio receiver the combination of means for receiving oscillations which include transmitted signals and disturbances, a local oscillator operative with the freq'uency and in phase with the signal oscillations, means for combining said signal and disturbance oscillations with the in-phase -oscillations of said oscillator to produce -a quantity a-l-b cos wherein a is the signal amplitude, b the disturbance amplitude and o the phase angle between the signal to be received and the disturbance of the same frequency, means for combining, out of phase, the signal and disturbance oscillations with the oscillations of said oscillator to produce a quantityb sin means for transforming the quantity b sin 15 into the quantitylb cos c, and

means for subtracting the last-mentioned quantity from the quantity a-l-b cos zb.

7, In a system according to claim 6 the combination of 'a diode and an external resistance as a squarel law translating device for quantities such as said quantity b sin rp.

8. A system according to claim 6 comprising an electron discharge tube having a lower curved part of its characteristic adapted to serve as'a means for squaring quantities such as b sin c.

9. A system according to claim 6 comprising an lelectron discharge tube having an upper curved part of its characteristic adapted to serve as a means'for extracting the root of quantities such as b2 cos2 1.

10. A system according to'claim 6 comprising a cathode ray tube adapted to produce the square of a .quantity such as b sin 41 and the square root of a quantity suchas b2 cos2 qb. i

v f ZOLTAN BAY.

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