US2293565A - Diversity receiving system - Google Patents

Description

Aug. 18, 1942. R. E. SCHOCK DIVERSITY RECEIVING SYSTEM Filed April 30, 1941 '3 Sheets-Sheet 1 TO U T/L/ZA T/ON 05 VIC E Sc. 6. POTENTIAL 56. G. POTENTIAL INVENTOR ROBERT E. SCI-IOCK ATTORNEY qvfiznfimm w m @3253 w m m m-+v i Mia a 0 m. .Y NM Q m Mm NE R T m .u n. wk T H l l n l v w ll Y Qv h wmw R B F m H -m m m q m MW J I R W I w :v mm %m Q m: fizm mwuw w v wtzm mdum MN E235 mi mi a K v 3 M v E2213 Y W i j I b W NN Aug. 18, 1942.

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DIVERSITY RECEIVING SYSTEM Filed April 30, 1941 5 Sheets-Sheet 3 V gman T0 UTILIZATION DEV/C(E Ffg. 3

Patented Aug. 18, 1942 UNITED DIVERSITY RECEIVING SYSTEM Robert E. Schock, Riverhead, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application April 30, 1941, Serial No. 391,055

8 Claims.

This invention relates to radio reception and more particularly to a diversity receiving system in which, in connection with several signal receiving circuit arrangements, means are provided for avoiding the cancellation of the signals when they are combined out of phase.

In radio signalling, and particularly in connection with short wave reception, the phenomenon known as fading results in considerable variation in the volume and quality of the signal from time to time. It is well known in the art that if a simple combination of two signals of a diversity system is adopted, there will be intervals when the signals will be out of phase and will cancel. It has heretofore been proposed to overcome this difficulty by providing several receivers each associated with separate antennae so arranged with respect to each other that the effect of fading will be different upon difierent receivers, means being provided to select from time to time the receiver which delivers the strongest signal.

In accordance with the present invention, however, it is possible to avoid cancellation of the signals when they arrive out of phase in the different channels. One of these channels is arranged to be blocked during out of phase periods. Another method which may be employed, however, according to my invention is that which provides reversal of the phase of the incoming signals in one of two channels of a diversity receiving system so that an in-phase combination of energies from the two channels may be obtained.

A principal object of my invention is to provide a simple circuit arrangement for a diversity receiving system in which, when signals are received out of phase by two separate antennae, the energy delivered by one of these antennae may be suppressed so as to avoid cancellation of the energy received by the other antenna.

Another object of my invention is to provide means in a diversity receiving system for avoiding the out-of-phase cancellation of effects of energy received on three or more separate antenna circuits.

It is still another object of my invention to provide means in a diversity receiving system for reversing the phase of energy collected by a single antenna and making an in-phase combination of this energy with energy derived from one or more other antennae upon which reception may from time to time be out of phase with the .first said antenna.

The invention will now be described in more detail, reference being made to the accompanying drawings, in which Figure 1 shows a circuit arrangement applicable to two receiving channels of a diversity system for carrying out my invention;

Fig. 2 shows an expansion of the system of Fig. 1 to the requirements of a diversity receiving system having three or more receiving channels and,

Fig. 3 shows a circuit arrangement for a diversity receiving system in which, when the signals are received on different channels in phase opposition, the energy derived from one antenna will be reversed in phase. This circuit arrangement shows further the technique involved in combining the energies from three or more antennae by reversal of certain out-of-phase components whenever they occur in any one or more of the separate channels.

Referring first to Fig. 1, I show therein two transformers I and 2 through which signal energy is fed from separate points of collection. Transformer l feeds to an amplifier tube 3 while transformer 2 feeds to an amplifier tube 4. The outputs from the tubes 3 and 4 combined and fed in parallel to a transformer l5. The secondary of this transformer is connected to any suitable utilization device.

The signal which is applied to the grid 1 of tube 3 is also applied through a blocking condenser 20 to the grid l3 of amplifier tube 9. Likewise the signal which is applied to the grid 8 of tube 4 is also applied through blocking condenser 2! to the grid l4 of an amplifier tube Ill. The outputs from tubes 9 and in are combined and fed in parallel to transformer l6 which in turn feeds a diode detector tube H.

The rectified voltage developed across a diode resistor [9 produces an effective shift of the terminal potentials of a direct current biasing source I8 with respect to ground. The bias potential applied through resistor l9, source I8, and the secondary of transformer 2 to the grid 8 of tube 4 renders this tube conductive so long as the tube ll continues to rectify signal energies that are in substantial phase agreement.

The output energies from tubes 3 and 4 will, under normally favorable conditions of reception, be additive and maximum power will be delivered to transformer l5 as a derivative of the two receiving channels.

Under conditions of phase opposition of the energies received on the two channels, however, it will be seen that a cancellation of energies would occur in the combined output of the tubes 3 and 4 providing their signal strengths during such time are equal or substantially equal. It, therefore, becomes necessary to out 01f the output from tube 4 and this is accomplished by shifting the bias applied to the grid 8 in the negative direction. The bias shift is accomplished by the failure of the rectifier tube I! to be fed with sufficient energy from the combined outputs of tubes 9 and E to cause an appreciable voltage drop in the resistor IS. The full negative bias voltage from the source H3 is, therefore, applied to the grid 8 in tube 4. This tube is thus blocked and delivers no out-of-ph'ase signals to the transformer I5.

Upon restoration of an in-phase relationship between the signals respectively fed to the tubes 9 and I0 from the different channels, the rectified energy in the detector tube H produces a voltage drop in the resistor I? which is opposed to the voltage of the biasing source i8. The normal bias is, therefore, restored to the grid 3 of tube 4 and the output from this tube is then added to that of tube 3. The phase relation between the signals in the respective receiving channels is, therefore, the controlling factor in governing the bias on the grid 8 of tube Referring now to Fig. 2, I show how the system of Fig. 1 may be extended to cover the combined action of signal energies derived from as many as three separate receiving antennae and associated circuits. The elements in combination, so far as they were shown and described in Fig. 1, are duplicated'in this Fig. 2 with the addition of further elements now .to be described.

The output energies from tubes 3 and are combined and fed to one side of the primary in transformer I5, as before. When tube 4 is blocked the signal is derived entirely from the output circuit of tube 3. A third source of signal energy may be fed through the transformer 22 to the grid 33 of tube 25. This tube operates in conjunction with the signal as amplified by tube 25 whose grid 28 receives its control from the secondary of transformer l5. The anode 21 of tube 25 and the anode 29 of tube '25 are interconnected and both circuits are combined in the primary winding of transformer 31.

Part of the signal energy derived from transformer I5 is diverted through blocking condenser 23 to the grid of a tube 3!. Likewise a part of the signal energy from the secondary of transformer 22 is diverted through blocking condenser 24 to the grid 34 of tube 32. Tubes 3| and function in exactly the same manner as tubes 9 and H] for the purpose of determining the phase relation between the signals in the two transformers I5 and 22. When these signals are in phase the resultant output energies from tubes 3| and 32 are such as to produce a rectifying action in the diode tube 39, energy being fed thereto across the transformer 38. Rectification of these energies produces a voltage drop in the resistor 40 which is opposed to the normal D. C. bias from the biasing source'4l applicable to the grid 30 in tube 26. Normally, then, when the signals fed across transformers i5 and 22 are substantially in phase agreement, tube 26 is maintained in the conductive state and its output energy is added to that of tube 25. When, however, phase opposition occurs, the signals fed to the grids of tubes 3| and 32 cancel out and the voltage drop in resistor is reduced to a negligible value. The full voltage of the biasing source 4| is then applied negatively to the grid 30 of tube 26 thereby blocking the same and permitting the output energy from the tube 25 to be applied across the transformer 31 without opposition.

Further diiplications of the circuit arrangements shown in Fig. 2 may, of course, be made as far as may be necessary to extend the comparisons between one set of channels and another. Thus any number of diversity signal channels may be combined in one utilization circuit.

Referring now to Fig. 3, I show a somewhat different embodiment of the invention, where, instead of discarding the signals in one of the channels, the phase of these signals may be reversed and then combined with the signalling energy from another channel. This circuit arrangement is described in detail as follows:

Two signals derived from respectively different antennas are fed across transformers 59 and 5|, each of whose secondaries is connected respectively to grid 54 in tube 52 and grid 55 in tube 53. The anodes 55 and 57 of the tubes 52 and 53 are interconnected and both are connected to the upper terminal of the primary in a transformer 51. This is a push-pull transformer having the positive terminal of an anode source connected to its center tap. A third tube 58 has its grid 55 controlled across blocking condenser M by signalling energy from transformer 5| in the same sense as the control of tube 53. The anode 50 of tube 58, however, is connected to the lower primary terminal of transformer 61.

The signals fed through transformers 5i! and 5| are also used to control the grids 53 and 64 respectively in another pair of tubes 6| and 62. These tubes have their anodes 65 and 66 interconnected so that they will feed in parallel through transformer 68 to a pair of diode detector tubes 69 and i6.

The diode tubes 69 and 76 are so connected as to produce full wave rectification of any energies which may be fed thereto acrosstransformer 68. The amount of energy rectified, however, depends at all times upon the .phase relation between the outputs from the tubes 5| and 62. If these outputs are in phase agreement then th amount of energy rectified will be a maxi mum and the voltages developed across the respective diode resistors H1 and 4! may be utilized in opposite senses as follows:

The negative voltage developed across a resistor 10 connected to the anode of diode tube 69 influences the bias on grid 59 in tube 53 in such manner as to block this tube under normal in-phase conditions of the signals appearing across transformers 5i) and 5|.

Also under normal conditions of phase agreement between the signals fed across transformers 5E! and 5| the tube 53 is maintained in a conductive state by virtue of the rectifying action in the diode 15 which produces a positive voltage drop across its resistor 41 connected in opposition to the normal D. C. biasing source 1|, whose negative terminal is connected through the secondary of transformer 5| to the grid 55 in tube 53.

Consider now the action of tubes BI and '62 and their associated circuits including the transformer '68 and the diode tubes 69 and 16 when phase opposition occurs between the signalling energies. The outputs from tubes 5| and 62 will substantially cancel out, leaving no energy to be rectified in the tubes 55 and 15. In the absence of appreciable voltage dropin the two resistors Iii and 4'! tube 58 will be rendered conductive while tube 53 will be substantially blocked. This is true because resistor 70 will no longer deliver a blocking bias potential to the grid 59 in tube 58 and because, at the same time, the resistor 41 will offer no opposing voltage to that of the D, C. source H, in which case this latter source will be fully effective in producing a blocking bias upon the grid 55 in tube 53. Under these conditions of phase opposition, therefore, tubes 52 and 58 will cooperate, each delivering signalling energy to its appropriate one of the opposing terminals of the primary in transformer 61. The signals being in phase opposition, however, their push-pull combination in the transformer will be additive.

Fig. 3 also discloses an expansion of the system of combining phase-opposed signals from two channels so that further combinations of signals in and out of phase may be made as when reception is derived from three or more antennas. The same principles of utilizing combining circuits are involved as in the case of the embodiment shown in Fig. 2.

Assume now that the signalling energy is collected by three separate antennas feeding respectively to transformers 50, 5| and 15. The output from transformer 15 controls the grid 19 in tube 11 and also (across condenser 98) the grid 83 in tube 82. Tube 11 performs in the same manner as tube-53, whereas tube 82 fulfills the same function as that of tube 58 but with respect to the signalling energy from a different antenna.

Likewise the pair of tubes 85, 88 is utilized to compare the phases between the signalling energies derived across transformers 61 and 15 respectively. Furthermore, the combining of output energy from tubes 85 and 88 in or out of phase renders the diode tubes 93 and 99 more or less conductive in dependence upon the phase relation of the signals. These diodes are arranged to deliver separate half-wave rectification components of energy induced across transformer 92. The anode of diode tube 93 has associated therewith a resistor 94 and a grid biasing circuit leading to the grid 83 in tube 82. Also the diode tube 99 has its cathode connected to a resistor I and also to the positive terminal of a D. C. biasing source 95, the negative terminal whereof is connected through the secondary of transformer 15 to the grid 19 of tube 11. The anodes 8| and 89 of the respective tubes 11 and 16 are interconnected and are arranged to feed output energies to the upper terminal of the primary in transformer 9 I. This transformer is similar to and fulfills corresponding functions with respect to those of transformer 6'l When the phase of the signals in transformers l and His in agreement, or substantially so, then the tubes 16 and T! operate as a team, feeding their signalling energy across transformer 9| to the utilization device. At the same time the tubes 85 and 83 operate as a team and their output energies are combined and delivered across transformer 92 to the diode tubes 93 and 99. These tubes then fulfill the same functions as diode tubes 69 and 16. That is to say, when the signals are in substantial phase agreement the voltage drop in resistor 94 causes tube 82 to be blocked, while the voltage drop in resistor I09 (opposed to the voltage of the biasing source 95) causes tube 11 to be rendered conductive. This tube and tube 16 then work together as a team in supplying signalling energy to the upper terminal of the primary in transformer 9|.

In the case of phase opposition between the signalling energy in transformer 6'! and 15, tube 11 becomes blocked and tube 82 becomes conductive, but since the anode 84 in tube 82 is connected to the lower terminal of the primary in transformer 91 these phase opposed signals produce an additive effect in respect to the signalling energy derived from transformer 67 and amplified by tube 16.

The combining circuits herein shown and described may be used in radio frequency stages or in intermediate frequency stages, depending upon the requirements of the circuit arrangements.

Various modifications of my invention may be made by those skilled in the art without departing from the spirit and scope of the invention itself. The invention is limited, therefore, only in accordance with the claims.

I claim:

1. In a diversity receiving system, a plurality of receiving circuits each fed with Wave energy from an appropriate antenna, combining circuit means comprising amplifier discharge tubes in-' dividual to each receiving circuit and having a common output circuit, means including a grid biasing source operative to maintain a cut-ofi bias on the control grid of at least one of said amplifier tubes in the absence of substantial phase agreement between the energies derived from said receiving circuits, and means responsive to variations in the phase relation between the wave energies fed through said receiving circuits respectively for deriving a rectified signal energy component which is opposed to said cut-off bias, the two means last recited being cooperative to render the signal energies of the respective receiving circuits additive during periods of substantial phase agreement, and to suppress the amplification of energy in the tube whose control grid is connected to said biasing source during periods of substantial phase opposition of the energies in said receiving circuits.

2. In a system according to claim 1, a first pair and a second pair of amplifier discharge tubes comprised in the first said means, each tube of the first pair and one of the tubes of the second pair having its control grid connected to a respective one of said receiving circuits, the remaining tube of the second pair having its control grid coupled to the common output circuit of the first pair, and an additional common output circuit for the second pair.

3. In a system according to claim 1, the elements so defined in combination with amplification means operative only when the amplification of phase-opposed energy is suppressed for delivering a useful component of said energy to said combining circuit means in a push-pull manner.

4. In combination, a plurality of diversity receiving circuits each individual to a differently situated antenna, a single amplification path in one of said receiving circuits, oppositely phased amplification paths in the remainder of said receiving circuits, phase comparison means operative in respect to a pair of said amplification paths, and switching means operative in dependence upon the instantaneous determinations of said phase comparison means whereby one of said oppositely phased amplification paths is selected to the exclusion of the other, and means for combining the energy delivered by the select-, ed amplification path with that delivered by said single amplification path.

5. The combination according to claim 4 and including at least three of said receiving circuits,

said phase comparison means comprising different sections each appropriate to a different group of said receiving circuits.

6. In a diversity receiving system, a pair of diversity receiving circuits, an amplifier for one of said circuits, two amplifiers for the other of said circuits, an output transformer having one terminal of its primary winding connected in common to corresponding output leads from the first said amplifier and from one of the other two amplifiers, a connection from the other primary terminal to the corresponding output lead from the remaining amplifier, and means operative in dependence upon variations in the phase relations between the input energies respectively fed to the several amplifiers of said receiving circuits for causing the output energies thereof to be at all times combined in aiding relation to one another in said transformer.

'7. The combination according to claim 6 wherein the last said means comprises a device for amplifying a diverted part of the energy from each receiving circuit, means for combining and detecting said diverted energies, and gain control devices operative as a voltage function of the combined and detected energy for enabling one of the two amplifiers for one receiving circuit to amplify while blocking the other of said two amplifiers.

8. In a diversity receiving system, the device as defined by claim 6 in combination with a third receiving circuit, two amplifiers for said third receiving circuit, an amplifier having an input circuit fed with energy from said output transformer,.a second output transformer having one terminal of its primary winding connected in common to corresponding output leads from the amplifier last mentioned and one of the two amplifiers of said third receiving circuit, a connection from the other primary terminal of said second output transformer to the corresponding output lead from the remaining amplifier of said third receiving circuit, and means operative in dependence upon the phase of the input energy fed to the two amplifiers of said third receiving circuit in relation to the phase of the energy delivered to the first said transformer for causing the output energies derived from each of said amplifiers to be either suppressed or combined in aiding relation to one another in said second output transformer.

ROBERT E. SCHOCK.

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