US2269011A

US2269011A - Method and arrangement for limiting interferences in radio receiving apparatus

Info

Publication number: US2269011A
Application number: US316469A
Authority: US
Inventors: Dallos George
Original assignee: MAGYAR WOLFRAMLAMPA GYAR KREME
Current assignee: MAGYAR WOLFRAMLAMPA GYAR KREME
Priority date: 1938-10-28
Filing date: 1940-01-31
Publication date: 1942-01-06
Anticipated expiration: 1959-01-06

Description

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METHOD AND ARRANGEMENT. FOR LIMITING INTERFERENCES IN RADIO RECEIVING APPARATUS Filed Jan. 3l, 1940 4 SheetSfShvee'b 2 JMJ looo zooo ooo n 4o'oo sooo Jan. 6, `1942. Q DALLos y METHOD AND ARRANGEMENT FOR LINITING INTERFERENCES IN RADIO RECEIVING APPARATUS Filed Jan. 3l, 1940 4 Sheets-Sheet lE5 je @jalea/ s Arronuley Jan. 6, 1942.

I ALLos 2,269,011 METHOD AND ARRANGEMENT FOR LIMITING INTERFERENGES vIN RADIO RECEIVING APPARATUS -Filed Jan. 31, 1940 .,4 Sheets-Sheet 4 SIW n l l gp l Ll.

yMmZ'E/z feo/7e v y Afm 5m LT-TQANEY Patented Jan. 6, 1942 METHOD AND ARRANGEMENT FOR LIlYIIT- ING INTERFERENCES IN RADIO RECEIV- ING APPARATUS George Dallos, Budapest, Hungary, assignor to- Magyar Wolframlmpa Gyr Kremenezky Jnos Rszvnytrsasg, Budapest, Hungary, a Hungarian company Application January 31, 1940, Serial No. 316,469 In Hungary October 28, 1938 8 Claims.

It is known that the oscillatory circuits of a radio receiver are disturbed by an aperiodic voltage impulse, that is to say an interfering impulse, which is received by the receiver. The Fourier analysis of the resulting interference curve shows that the voltage produced by the interfering impulse throughout the whole of the usual reception range `of approximately 9 kilocycles contains components which have approxi'- mately equal amplitudes, so that the interference forms as it were a continuous spectrum independently of the duration of the interfering impulse. On the other hand, the frequency distribution of the modulation is discontinuous, that is to say the places where modulation occurs and the amplitudes of the frequencies contained in the modulation are determined by the sound to be transmitted. Itmay happen, for example in the case of awomans voice, that the higher sound frequencies predominate and that the lower frequencies are almost entirely absent. This distribution of frequency may take place in the most varied ways in thevsound to be transmitted. Y f

It has previously been proposed to subdivide the receiving band received into a plurality of channels and to eliminate interference by amplitude limitation in the individual channels and especially in those comprising the high sound frequencies. The effect of the interference is not limited by this method to any substantially greater extent than by those known methods which prevent a sudden increase in sound frequency amplitude beyond the maximum amplitude corresponding, for example, to 100% modulation. The reason for Athis is that, on the one hand in each of the channels in which an amplitude limitation takes place the adjustment of the biassing voltage of the limiting device is indeterminate because this vdepends on the average value of the high frequency carrier wave, vand on'the other hand elimination of interference is effected only in a part of the frequency band, no account being paid to the continuous course of the interference spectrum.

. It has also been proposed to eliminate interference in a receiver in dependence on the degree of modulation. This method, in addition to the difficulty of carrying it into effect, has the disadvantage that the limiting level is determined by the greatest amplitude existing in the sound frequency band and is independent of the frequency.

vBy the method of they present invention the are obviated and at the same time excellent results in the elimination of interference are obv tained, since the interference is suppressed to the same extent as useful signals are received in the receiver. In this way, the difference between the interference and the signal, namely that the spectrum of the interference is continuous and that of the signal is discontinuous, is fully utilized.

According to the present invention, there are used for the further transmission of the instantaneous signal frequencies only those channels of the receiving band in which a component of the vinstantaneous signal occurs and the magnitude of the voltages which can be passed through the individual channels is'made dependent on the amplitude of the signal frequencies in the channel in question.

In one method of carrying out the invention aseparate amplitude. limiting device is connected in each individual channel in the low. frequency part of the receiving apparatus, and the limiting voltage for the amplitude limiting device is determined by the component of the signal frequencies in the channel' in question.` For pro-A ducing the limiting voltage for the amplitude limiting device the component of the signal frequencies inthe channel can be supplied to a rectifying stage which is connected through a filter circuit with the lamplitude limiting device. Inl order that the invention may be readily understood and easily carried into effect it will now be described by Way of example with reference to the accompanying drawings, in which Figures 13 each represent a sound diagram divided into a plurality of channels.

c Figure 4` is a diagrammatic representation of an arrangement having a plurality of channels which is suitable for carrying out the method of the invention, and

, Figure 5 is a circuit diagram of one of the channels of the arrangement shown in Figure 4.

In Figures 13 the frequencies in cycles per second are plotted as abscissae and the sound frequency energy E in any unit is plotted as ordinates.

Referring to the response diagram illustrated in Figure 1, the frequency` band which extends up to 5000 cycles per second is divided into eleven channels designated I-Il ,1 and the sound-frequency energy in eachvchannel at the moment of investigation is indicated in each channel by a thick vertical line. The curve gl represents the distribution of theinterference components disadvantages of the above-mentioned methods in each of the channels.` In the diagram of Figure 1 there is no signal component in the

channels

2, 5, 6 and while on the other hand signal components exist in the

channels

3, 4, 1, 8, 9 and |0. For the transmission of this sound it is therefore sufcient if the last mentioned channels are allowed to function and the former channels are prevented from being effective. It

follows from this that only the interference com-V ponents which are present in the

channels

3, 4, 1, 8, 9 and |U are further transmitted while those in the channels l, 2, 5, 6 and Il are not transmitted further. If now there is connected in each of the

channels

3, 4, 1, 8, 9 and I9 an amplitude limiting device the limiting action of which is made dependent on the energy of the sound frequency components occurring in the individual channels, then as far as the area a, b,

c, d, bounded by the curve g, which represents the amount of interference, is concerned, only components which fall Within the field of the diagram which is not section-lined and which are insignificant and dov not interfere with the reception.

Figure 2 illustrates by way of example a further sound diagram. In this case, at the moment of making the investigation, the band is entirely cut off above a frequency of 2,300 cycles per second, so that the interfering components represented by the curve g2 which fall within the band above that frequency are entirely eliminated. Similarly as in Figure l, in this case only the interfering components below the line k2 and falling in the field which is not sectionlined are further transmitted.

The diagram of Figure 3 illustrates the theoretical case in which the receiving band is subdivided into a very great number of' channels and the reduction of interference is carried out in each channel. As may be seen from the diagram, it is possible by the method of the invention to reduce the interference to such an extent that it exactly follows the course of the sound diagram as is illustrated by the curve k3.

A diagram showing an arrangement suitable for carrying out the method of the invention is illustrated in Figure 4. In this figure the part of the apparatus up to the low frequency amplifier is indicated by the numeral 20. The references 2|-28 designate low frequency band pass filters by means of which the receiving band is split up into eight channels. The receiving circuits of the respective channels are represented by the rectangles indicating the filters. The nlters are connected respectively to amplitude limiters 3|-38 and these in turn are connected respectively to rectiers lll- 48 and the correspondingly filtered limiting voltages therefrom are conducted through the leads 5|-58 to the amplitude limiters. The separate channels are combined in the amplifier 60 which is connected through a second amplifier 6| to a loud speaker 62. Obviously the signal components belonging to the individual channels can be combined in any desired combination and may in some cases be conducted to separate loud speakers.

Figure 5 represents by way of 'example the circuit diagram of one of the channels. The terminals 1| and 12 are connected to the rst stage of the low frequency part of the apparatus. The signal components to be transmitted by the channel are separated from the complete low frequency signal occurring at the terminals 1| and 12 by the filter 13. IIThe signal components then pass through a condenser 14 to the control grid of a limiting valve 16 which is constructed as a pentode and is provided with a grid resistance 15. The valve 16 is connected in parallel (from a direct point of view) with a regulating valve 'l1 which is constructed as a triode and receives its anode voltage through a resistance 88. Between the anode lead and the earth connection of the valve 11 are interconnected potentiometer resistances 18 and 19 which are connected in series. The vconnecting point between the two resistances 18 and, 19 is connected to the primary winding of a transformer 8| the other end of which is connected to the anode of the valve 16. The secondary winding of the transformer 8| is connected to an amplifying valve 82 in the anode circuit of which is connected a condenser 84 as well as a choke 83 serving as a load impedance. The output terminals are indicated by 85 and 86. From this anode circuit is branched off through a condenser 81 the circuit of a diode 88 which is connected by way of the

filter

98 and 9| to the regulating valve 11. The diode 88 has a loading resistance 89 the tapping point of which is connected through the

filter

92 and 93 to the grid leak resistance 15 of the limiting valve 16. v

In order to be better able to understand the invention the operation of the circuit illustrated will be shortly described. If the anode voltage of the valve 16 is less than the voltage on its screen grid, a saturation characteristic is obtained of which the section of positive steepness enabling an undistorted amplification, varies according to the voltage on the positive electrodes of the valve. 'Ihe screen grid voltage and the anode voltage of the valve 16 are regulated by the triode 11. If the current flowing through the triode 11 increases, the voltage drop at the resistance becomes greater, the consequence of which is that screen grid and the anode of the Valve 16 receive a smaller voltage, whereby the limiting level is reduced. If, however, the current through the triode 11 falls the voltage on both the aforesaid electrodes increases as does also the limiting level. The oscillations limited in this way pass from the Valve 16 through the transformer 8| to the amplifying valve 82 and thence to the output terminals and 86.

The regulation of the bias voltage on the control grid of the regulating valve 11 and therefore of the strength of the current flowing through the triode in order that it may be a function of the sound frequency voltage, takes place in the following manner.- The sound frequency alternating voltage amplified in the amplifier 82 is rectified by the diode 88, the voltage at the resistance 89 of which is proportional to the instantaneous voltage occurring in the channel. This voltage is passed through the

filter

98, 9| and is then applied as a regulating voltage to the control grid of the valve 11. rIf the amplitude of the regulating voltage falls, that is to say if the negative bias voltage on the regulating valve 11 becomes less, the anode current flowing through this valve increases, so that, as stated previously, the limitingV level of the .-.velve 1.6 adjusts itself to. af ,lower .value corresponding f to )the 1-emp1itudefto. .be transmitted- Ifthe regulating .-yoltage e increases, the converse is the case andthe limiting "level -of the valve 16 is 'raised.L Thus theqlevel of limiting amplitude follows accurately the Vvamplitudes to. be transmitted. If the amplitude to be transmitted falls to z'ero, that is tosay ify there yis no signal component in the channel-in question, Athe transmission in the. channel is practically interrupted or at least reduced to a minimum. The biassing .voltage by which theworking pointof the valve 16 fis determined is also taken fromfthe resistance 89 and passed through

filter

92 and 93 andthe resistance l5 tothecontrol grid of the limiting A valve '16.

The filters 90, 9| and 92, 93 should be so dimensioned that their time factor is greater than the period of oscillation of the lowest signal frequency occurring in the channel in question.

The circuits of al1 the channels can be of the kind described. However, other amplitude limiting circuits can be used without affecting the invention in any Way. The limiting level in all the channels will rise or fall in accordance with the larger or smaller alternating voltages in the individual channels.- The effect illustrated in Figures 1-3 is therefore produced and the interference is practically entirely eliminated.

The same effect can also be obtained by dividing the high or intermediate frequency part of the receiving apparatus into a number of channels and rectifying the oscillations in the individual channels. In this case, however, the limiting voltage for the amplitude limiters connected in the individual channels must consist of two parts of which one is proportional to the average value of the high or intermediate frequency arriving in the bands in question, that is to say a slowly varying voltage While the other, on the other hand, is proportional to the amplitude of the modulation frequency in the band in question, that is to say is a rapidly varying voltage.

The highest permi-ssible number of channels is in any case such that the individual channels can follow the oscillations of the signal component to the full extent.

For carrying the invention into effect any desired and known device or circuit which effects a limiting effect can be used and it is only necessary to take care that the working characteristic of the limiting device possesses sharp lower and upper bends. l

The circuits in accordance with the invention can be combined with automatic band width regulators in such a way that the Width of the resonance curve and the place of the receiving band is made dependent on the modulation, that is to say that when the higher sound frequency components are absent in the modulation, the band Width is automaticaly reduced. Also any known tuning device can be used on the two receiving side bands which functions in such a way that if many high sound frequency components but no low sound frequency components are present in the receiving band, the receiving band is shifted from the carrier to the right or to the left. There is thus obtained a band Width regulation operating as a function of the modulation Which results in better reception. The band Width regulator or automatic tuning device described is employed in the high or intermediate frequency part of the apparatus.

What I claim is:

1. In the method of limiting interference in radio reception iny which the band received-fis split up into a plurality of sub-bands--they im- Vthe other sub-bandsto a value dependent on the maximum amplitude of the instantaneous signal frequency therein to thereby permit transmission Y ineach sub-band in Which an instantaneous sigynal frequency occurs of only those interfering components having' amplitudes not substantially greater than the. maximum amplitude of the instantaneous signalmfrequency therein.

2.,A In a radio receiving system includingv a plurality of filter-provided channels for dividing the total frequency band'of the system into as `many subbands, and .wherein only those channels are active at leach instant in which components of received signal frequencies occur, the combination with each rchannel of an amplitude limiter, means connected to each of said amplitude limiters to receive audio frequency alternating voltages, means for transforming voltages received by each of said first-mentioned means into controlling voltages for the amplitude limiter connected thereto, and means for applying said controlling voltages to the respective amplitude limiters so as to limit the maximum voltage passing through the particular channel.

3. A system as claimed in claim 2 in which each filter circuit has a time factor greater than the period of oscillation of the lowest signal frequency occurring in the'particular circuit.

4. A system as claimed in claim 2 in which each amplitude limiter comprises a multi-grid valve having a screen grid and an anode .which is at a less positive potential than the screen grid.

5. In a radio receiving system including in a stage higher than a low frequency stage, a plurality of filter-provided channels for dividing the total frequency band of the system in as many subbands, and wherein only those channels are active at each instant, in which components of received signal frequencies occur, the combination, with each channel, of an amplitude limiter, means connected to each amplitude limiter for rectifying the oscillations in the particular channel, a two-part means for applying controlling voltage to said amplitude limiter, one of said parts being adapted to supply one part of the controlling voltage in proportion to the average amplitude 'of the frequency in the particular channel, the other one beingl adapted to supply yanother part of said voltage in proportion to the amplitude of the modulationfrequency in the particular channel.

6. In the method of limiting interference in radio reception in which the band received is split up into a plurality of sub-bands, the improvement which consists in substantially preventing energy from being transmitted in those subbands in which no component of the instantaneous signal frequency occurs, and simultaneously limiting the maximum voltage in each of the other sub-bands to a value dependenton the maximum amplitude of the instantaneous signal frequency therein to thereby permit transmission in each sub-band in which an instantaneous signal frequency occurs of only those interfering components having amplitudes not substantially greater than the maximum amplitude of the instantaneous signal frequency therein and com- .bining the energy transmitted through the varlous sub-bands and supplying the combined energy to a sound reproducing device.

7. A radio receiving system comprising means for separating the received energy into a plurality of channels each of which covers a different band of frequencies, means for instantaneously preventing transmission of any energy through each channel in which there is no instantaneous component of the received signal, means for preventing the transmission through each channel in which a component of the received signal occurs of any interfering component of greater amplitude than the instantaneous signal frequency therein, and means for combining the energy transmitted through the various sub-bands and supplying the combined energy to a sound reproducing device.

8. A radio receiving system comprising means for separating the received signal energy into a plurality of channels each `of which covers a different band of frequencies, means connected in each channel for variably limiting the amplitude of voltages which may be passed therethrough, means operable by received signal frequency in the frequency band of each channel to operate the limiting means of ysuch channel to permit the sage through 'such channel of only those interfering components having amplitude approximatelyequal to or less than the maximum amplitude of signal frequency instantaneously passed through the channel.

GEORGE DALLOS.