US2289444A - System of transmission and reception - Google Patents

Description

y 1942'- H. MAYR 2,289,444

SYSTEM OF TRANSMISSION AND RECEPTION Filed Feb. 17, 1939 3 Sheets-Sheet 1 W g wk w July 14, 1942. H. MAYR SYSTEM OF TRANSMISSION AND RECEPTION Filed Feb. 17, 1939 's Sheets-Sheet 2 July 14; 1942; H, AYR 4 2,289,444

SYSTEM OF TRANSMISSIONAND iRECEP'I'ION Filed Feb. 17, 19:59 a Sheets-Sheet s Jame/Mm Patented July 14, 1942 1 SYSTEM OF TRANSMISSION AND RECEPTION Hermann Mayr, Paris, France Application February 17, 1939, Serial No. 257,003 In France February 24, 1938 Claims.

This invention relates to a radio communication system embodying a combined portable transmitter and receiver, common parts of which operate for the purpose of signal transmission and reception.

It is the object of the present invention to provide a compact and rugged portable unit embodying a transmitter and receiver for commu nication-signalling.

It is a further object of the invention to associate with the portable transmitting station an aerial connection which serves simultaneously for reception and transmission at highest efficiency.

It is old to employ combined apparatus for the simultaneous transmission and reception of messages or communications by wireless telegraphy. In apparatus of this type as used at the present time one apparatus functions for reception and the other produces the transmission, both apparatus being mounted in a single casing or housing. Generally two aerials are required for greater efiiciency.

This combination presents numerous disadvantages, the most important of which are:

1. The reception is considerably impeded by the harmonics of the transmitter, as each harmonic may combine with the frequency of the oscillator of the superheterodyne receiver to produce an obstructing hissing or whistling.

2. It is also necessary to have two aerials.

3. Finally, it is necessary to have two different apparatus: transmitter and receiver.

According to the present improvements, these defects are eliminated in that use is made of an apparatus which operates both as transmitter and receiver, only one aerial being required, and certain members are used commonly for reception and transmission.

The different characteristic features of the invention are described in the following specification, with reference to the accompanying drawings which show several features of the invention.

Figure 1 is a circuit diagram of a station constructed in accordance with the present invention;

Figure 2 illustrates the principles of the aerial connections in the present arrangement;

Figure 3 shows the improved aerial circuit functioning for both transmitting and receiving the radiant energy;

Figure 4 shows a modified arrangement of the circuit shown in Figure 1;

Figure 4a represents a variation of the coupling arrangement between the antenna, transmitter and receiver from that shown in Figure 4;

Figure 5 illustrates a different embodiment of the invention illustrated in Figures 1 and 4; and

Figure 6 is a modified arrangement of a portion of the circuit shown in Figure 4.

In the arrangement shown in Figure 1, the receiver is of the superheterodyne type and requires, as known, the use of a local oscillator. The transmitter has its oscillating circuit L1C1 which serves as an oscillator for the local frequency of the superheterodyne receiver. This same circuit L101 forms the pilot for the transmission. Its aerial connection is constructed according to the principles described in greater detail below in connection with Figures 2 and 3. This coupling is provided by the circuit L2C2, and the transmitter is modulated by the modulator comprising the audion tubes V4 and V3, i. e., modulation by plate and transformer.

As to the reception, it is effected by means of a conventional superheterodyne receiver in which V6 is the initial detector or modulator. The oscillator for the local frequency is formed by V1 and V2. The intermediate frequency stage is V5 and the two stages V4 and V3 then serve as low frequency amplifiers, as described in greater detailbelow.

The characteristic features of the invention are therefore the following:

1. The circuit L1C1 serves as a pilot for the transmitter and is used at the same time and simultaneously as an oscillator in the reception to produce the local frequency. This circuit is connected by the coil L3 to the modulator V6. Inasmuch as the oscillation of the pilot is very strong relative to modulator Vs the connection between L3 and L4 is very loose.

2. There is but one aerial which is connected for the transmission in the circuit 202, said circuit being tuned to the frequency of the cir- I cuit L101; the aerial is also connected with the circuit L404 of the reception modulator by the capacity C5. The aerial may be connected at the same time in the two circuits without losses, because these two circuits L202 and L401 are of greatly different frequency.

3. The audion V4 serves as an amplifier for the reception and the microphone M1, and likewise as a detector by means of the diode plate D1. The transformer T1, which is connected to V4. by its secondary S1, amplifies, on the one hand, part of the current detected by the diode D1 branched on the primary P2, and on the other hand the potentials of the microphone M1 connected with the primary Winding P1. V4. is then connected with V3 and the head set or loud speaker is branched from the plate circuit of V3 through the capacity C6.

The advantages of this method of mounting are: elimination of the action of the harmonics of the transmitter on the receiver, possibility of changing the frequency of the transmission by changing the value of the intermediate frequency, use of the apparatus for simultaneous reception and transmission.

In the circuit diagram shown in Figure 1, the oscillator tubes V1 and V2 are indicated as pentodes operating in the conventional manner with the cathode control grid 2, screen grid 3, and the suppressor grid 4 in addition to the plate 5. The tubes are connected in a balanced or pushpull arrangement with the branched inductance L1 in the plate circuit and with branched inductances or resistors in the grid circuit. The initial detector V6 is likewise a pentode tube operating in a conventional manner and the same is true of the power pentode Vs operating in the final stage of audio-amplification for the low frequency signalling energy for transmission and for the detected incoming energy of audible frequency which is passed through the condenser C6 to the receiving device R which may be a head set or a loud speaker. The oscillator energy is modulated by the division of the energy furnished the plates of the oscillator tubes V1, V2 and amplifier tube V3 connected at the trans former T4.

The signal-modulated intermediate frequency in the output circuit of the audion tube V6 is passed to the input circuit of the audion tube V for amplification across transformer T2. The latter is a tetrode containing a cathode I, control grid 2, screen grid i, and plate 5, and serves to amplify the intermediate frequency for transference across the intermediate frequency transformer T3 to one of the diode plates D1 of the duo-diode triode tube V4 which operates to detect the incoming signals for conduction to the primary winding P2 of the audio-transformer T1 for transference to the secondary circuit of this transformer wherefrom the signals are imposed across the control grid 3" and cathode I of the tube V4 which functions in this instance as a normal triode amplifier. A suitable high resistance choke coil Ch serves to isolate the detected audio-frequencies for conduction to the coil P2. The transformer T1 operates to transfer the audible frequencies which are transmitted from the station by the cooperation of the primary winding P1, in circuit with the microphone M1 and the battery source E, with the secondary circuit S1 of the transformer, the energy transfer from which may be modulated by a suitable potentiometer inserted therein.

Referring to the aerial and the connection thereof to the circuit L202, it is well known that, in order to obtain the greatest efficiency of an aerial, the connecting lead should be branched off or connected at a well defined and strictly calculated point thereof.

In the case, for example, of a vertical, single wire aerial, the electrical disturbances which arise therein cause the aerial to vibrate electrically like the acoustic vibration of a pipe Or horn, and that potential loops and nodes exist along the aerial each of which corresponds respectively aerial current.

Considering, for example, a Hertz aerial, of the half wave type (Figure 2), the curve V represents the distribution of the potential along the aerial A and the curve I that of the current. It is well known that the greatest efficiency is obtained if the aerial is branched off either at a or at a, at the point of a potential loop or of a current loop.

On the other hand, the end of the aerial lead should be branched off at a well defined point of the oscillating circuit of the transmitter or the input circuit of a receiver.

The result is that in aerial connections used at present difficulties arise in the aerial which call for corrective attempts therefor which may prove obstructive if not incompatible with the desired use, particularly for low power, and above all for portable stations.

The present invention is designed to eliminate these defects.

For this purpose it is characterized by the fact that the aerial is connected, ordinarily by one of its ends, to an oscillatory circuit, the specific frequency of which is that of the transmission or the reception, and which is connected neither with the ground, with a counterpoise, to the earth, to another aerial, nor to another circuit.

This oscillating circuit is connected with the last stage of the generator system in the case of the transmission, or with the first circuit of the amplifying system in the case of the receivr, and it is tuned equally to the frequency to be transmitted or received.

Figure 3 shows an exemplary embodiment of this mounting:

1. The aerial radiates at maximum efficiency compatible with its dimensions, whatever be its length.

2. The aerial may be connected without it being necessary to modify the tuning; (the latter should be prohibited).

3. The connecting cable between the oscillatory circuit and the aerial proper or the outer part of the aerial, contributes for its part in the radiation, so that it may be considered as forming an integral part of the aerial which is an obvious advantage in the case of a portable station.

4. It is not necessary to seek the point of the oscillating circuit with which the cable is to be connected because, according to the invention, this point should be at the end of this circuit opposite the galvanometer, point a in Figure 3.

5. The only regulation to be made is thus to tune the oscillating circuit of the aerial O to the frequency of the wave generator, which is done simply by seeking the position of the variable condenser for which the deviation of the galvanometer is maximum, the aerial being disconnected.

It is, of course, advantageous to select an aerial which has potential loops at both its ends.

It is also possible to employ a connecting cable or feeder connected at a potential center which is not an aerial end, but in this case, for greater efiiciency, it is necessary to give the feeder a length dependent on the Wave length to be transmitted or received.

Figure 3 is a diagram of the aerial connection according to the invention.

The aerial A, of the semi-wave type for example, is connected at its end a, the seat of a potential loop, to the oscillatory circuit 0 tuned to the transmission frequency, that of the transmitter circuit 0' of the station, for example,

which is also, preferably, the frequency for which the aerial A has been constructed.

In the connection of the present invention, the tuning of the aerial, the control and. energy of the transmission are obtained immediately. It is possible to verify the tuning of the aerial circuit and measure the transmisison intensity whether the aerial is connected or not.

As a matter of fact, the aerial is regulated by regulating the aerial circuit for the transmission frequency, the aerial being disconnected. This regulation is obtained when a measuring instrument M indicates the greatest possible deviation. When the aerial circuit 0 is tuned to the transmission frequency without the aerial and when the latter is connected the instrument M should no longer move, or should move only slightly. If the aerial is too long the needle will have a smaller amplitude which, on the contrary, is increased if the aerial is too short. At any rate, the transmission frequency is not deranged because the oscillatory circuit 0 of the transmitter has itself not been modified.

Experience has demonstrated that, in order to have the best radiation at the moment in which the instrument M indicates the maximum intensity, i. e., with the aerial disconnected, it is necessary to mount the latter in the branch of the circuit 0 opposite the take-off contact or the like a of the aerial with respect to the capacity C and the self-induction B.

Finally, another important advantage of this connection system is that it completely eliminates the use of ground connections or counterpoises.

Figure 4 shows a modified circuit arrangement of the combined transmitter and receiver illustrated in Figure 1. Corresponding elements are designated by the same reference characters. The audion tubes V1 and V2 are shown as tetrodes of the EL2 type (French tubes). These tubes are arranged in an untuned grid, tuned plate, push-pull oscillating circuit. The control grids 2 of audion tubes V1 and V2 are connected to the branched inductance L7 while the plate circuit contains the branched inductance L1, which plate circuit is tuned by the variable condenser C1 in parallel with the fixed condenser C The screen grids 3 of the audion tubes V1 and V2 are connected with the plates 5. Pentodes may be utilized in lieu of the tubes as shown.

The energy for the receiver is conducted along conductor W containing the coupling condenser C5 which is connected with the tuned circuit L4C4. In view of the fact that the conductor W is .connected to the oscillator output circuit at a potential loop thereof, the inherent capacity to ground is adequate to complete the coupling circuit between the grid of the tube V6 and the cathode thereof which is grounded. The initial detector V6 is a .pentode of the EFs type (French tube) which operates as a mixer for the local oscillations and the incoming radiant energy, both of which are led in along the conductor W. The signal-modulated intermediate frequency appearing in the output circuit of this tube is transferred to the amplifying tube V5 through the intermediary of the coupling transformer T2. V5 is a pentode tube, type EF5 (French tube), the output of which is fed to the transformer T3 which feeds the energy to the duo-diode triode tube V4 for rectification of the signal energy. The tube V4 may be of the EBCa or EFe type (French tubes). The detected energy appearing on the diode element is imposed across a resistor F having a variable contact F associated therewith to take off a variable amount of received energy for conduction to the control grid 2 of the audion tube V4, operating as a triode, for amplification as explained above. This method of derivation of the detected energy for application to the input of the amplification stages V4 and V3 represents a departure from the corresponding arrangement shown in Figure 1 utilizing two primary windings on transformer T1 for the transmitted and received signals, although the latter may be employed alternatively, in which case the secondary of the transformer is grounded. The transmitted signals are .produced and amplified before modulating the oscillating energy in the same manner as explained in conjunction with Figure 1. Coil l0 operates as a radio-frequency choke to segregate the high frequency energy from the audio-frequency circuits.

Figure 4a. represents a variation of the coupling means between the antenna, transmitter and receiver circuit from that shown in Figure 4. The output of the oscillating circuit L1C1 is ,coupled to the coil La for transmission and reception and the inductance coil L9 in the conductor W2 serves to couple the local oscillations and the incoming energy with the circuit L404 in the input of the initial detector V6, whereupon the energy is detected, amplified, and finally detected and amplified, as explained in detail above. The energizing potential for the oscillator tubes V1 and V2 is derived from a source B which is common to both the last stage of the audio frequency energy and the oscillatory energy to modulate the latter in accordance with the well known principles of plate modulation.

Variations in the arrangements of the circuits shown in Figures 1 and 4 may be desirable in view of the following existing conditions:

1. The oscillations of the circuit C1L1 which serves at the same time for transmitting and receiving, have to be in a certain ratio with those of the circuit of the first detector of the receiver L404, whereby it ensues that the power of the transmitter is limited.

2. The oscillator C'1L1, V1V2 is modulated.

Arrangements can easily be made for the oscillator, which serves at the same time for the local frequency and for the transmission, not to be modulated and for it no longer to be dependent on energy level required by the receiver, for example, by taking a high frequency amplifying stage for the transmission as shown in Figure 5. In this case, it will obviously be possible to use a powerful transmitter. Of course, other stages such as a plurality of amplifying stages, frequency multiplying stages (frequency doublers), boosting stages, etc., can be used.

The modulation of the oscillator, as shown in Figures 1 and 4 may be found objectionable by reason of the instability of frequency and also by the fact that ones own voice is heard loudly in the headphones. As stated above, this objection can be eliminated by a circuit arrangement as shown in Figure 5. It is, of course, possible to use two separate low frequency amplifications, one for the modulation of the transmission and the other 'for the reception, so as not to be inconvenienced by ones own voice, as explained above, but the instability characteristics still remains.

For example, if it is desired to construct a transmitting receiving station which is as small as possible, the circuit shown in Figure 4 may be followed and instead of using for the low frequency stages, tubes EBCs and ELz as pentodes, corresponding to audions V4 and V3, respectively, the following combination can be used: one EBC3, corresponding to audion tube V4, one EL2 operating as a triode corresponding to V3, and a second ELz tube operating as a triode for the output tube. This arrangement is shown in Figure 6 and the last tube is indicated by V7. In this case the headphones R will be connected after the intermediate audion tube V3, type EL2, and an amply sufiicient amplification will be obtained for listening with the headphones R by two low frequency stages connected as triodes, and a perfect modulation for the transmission is had by three stages of low frequency connected as triodes preceding the modulation transformer T4 (Figure 6). This figure also shows a modified arrangement for feeding the low frequency energy to be transmitted from the transformer T1 to the input of the first low frequency amplifying stage V4. The arrangement shown in this figure may be applied to the circuits shown in either Figures 1 and 4.

In Figure 5, the circuit C1L1, with the valve V11, forms the master oscillator or pilot oscillator. The latter is connected to the high frequency amplifying stage V12 by the link l1. This high frequency stage is modulated by the modulator VrsVrz. Consequently, the master oscillator for the transmitter which is at the same time an oscillator for the local frequency required for receiving, is not modulated and the final power of the transmitter no longer depends on the master oscillator. The oscillations of the circuit C1L1 are coupled to the circuit C2L2 by the link I2. The audion tube V13, which is the first detector, can therefore be properly coupled with the oscillator. It is an easy matter to use such a tube for the oscillator that the oscillation thereof is suitable for the local frequency with respect to the first detector and also 'for the pilot with respect to the transmission. After the first detector V13, comes the intermediate frequency valve V14, then the combined second detector and first low frequency amplifying tube V15, and finally the second low frequency amplifying tube V16.

In the Duplex communication system, according to the invention, when two superheterodyne sets are in communication, one operates on the upper beat, the other on the lower beat, since if fl is called the transmission frequency of one of the sets, f2 that of the other and F the intermediate frequency:

Consequently, if it is assumed that there are several stations of this kind, they are divided into two groups, group I with the upper beat and group II with the lower beat. The stations of group I can only get into communication with those of group II, and conversely.

If it is desired to place one station of a group in communication with another station of the same group, the invention provides the possi- .bility of instantly modifying the set so as to make it similar to those of the other group.

For this purpose, a device is provided which, by means of a simple operation, enables the relation to be modified between the tuning'of the input circuit and that of the oscillator .and optionally of other circuits that it might be useful to modify.

An exemplary embodiment consists in providing a fixed condenser which is connected, by means of a switch, in parallel with the oscillator condenser. Moreover, said condenser may be replaced if necessary by several condensers or inductances or again by more complicated circuits. Another exemplary embodiment in the case of a single control, consists in giving a different setting at will to the two condensers or two groups of variable condensers.

When two apparatus similar to those described above are in communication and when the selectivity of the receivers is such that accidental variations of frequency produce weakenings at the receiving end which are inconvenient, the invention provides the use of automatic tuning devices of the known type, which act on the frequency of the oscillator. The advantages of such a device applied to the present apparatus is quite particular since it suffices for one of the apparatus to be provided with the system, owing to the fact that when one apparatus correctly receives the transmissions of the other,

the latter is automaticaly tuned to the transmis-- sions of the former.

This property of the sets according to the invention which are provided with the automatic tuning device, enables a two-way connection to be obtained while protecting the two correspondents from any third party intrusion. In fact, the invention provides for this purpose the continual and irregular variation of the transmission frequency of at least one of the sets. If the other set is provided with automatic tuning, it will automatically follow these variations of frequency. But the essential condition for the transmission frequency of the second set to tune itself to the reception of the first is that the intermediate frequency of the two sets be identical. It is precisely this latter condition which can serve as a protection from intrusions of third parties.

In the system according to the present invention, transmission and reception take place on two different frequencies. Taking the case, for example, of station I transmitting on a frequency of 7400 kc., the same is trapped at station II by means of a modulating circuit which is tuned to 7400 kc. If the intermediate frequency is 400 kc., the oscillator for reception at station II must be 7000 kc., for example. Since this same circuit serves as the oscillator for transmission, station II thus transmits on a frequency of 7 000 kc.

Thus it may be seen that in the case when the transmission wave of station II is 7000 kc., and that of station I 7400 kc., it is possible for a number of stations having a frequency of 7000 kc., to communicate with a number of other stations operating on a frequency of 7400 kc. However, it is not possible for the stations II, III, IV, etc., which transmit on 7000 kc., to communicate with each other. Thus, station II cannot communicate with station III. This is impossible because both operate on the same frequency.

The following system gives rise to the possibility set forth below:

Assuming that station I operating on a frequency of 7000 kc., but using at this time an intermediate frequency of 30 kc., station II must then transmit on a frequency of 7030 kc. It is now easy to use a receiver which does not exceed a selectivity of 30 kc. Automatically the tion. In other words, one person may interrupt the other while the latter is speaking and the former may be heard. The transmitter and receiver are combined in a compact single unit whichmay be energized by batteries, a generator, or directly from power lines.

In addition to the features above, the apparatus is characterized by the use of a single aerial,

which is simple in construction, which may be tuned easily and connected for highest efliciency. Reception cannot be altered by harmonics of the transmitter or be blocked thereby. Since reception and transmission take place on different wave lengths, a third person may hear only one transmitter at a time. The transmission frequency for both stations may be changed easily, rapidly and automatically by changing the value of the intermediate frequency of the receiving circuit.

What I claim is:

1. The method of intelligence transmission and reception utilizing in part a common amplifier which comprises generating oscillations locally for the dual purpose of modulation by the signals to be transmitted and for mixing with the received signal energy, amplifying the signals to be transmitted prior to the modulation of the local oscillations thereby, modulating the local oscillations with the outgoing amplified signals, receiving the incoming signal energy and mixing the locally generated oscillations therewith, and amplifying the received signal energy subsequent to the interaction of said local oscillations therewith, with the same amplifier executing the firstmentioned amplifying operation.

2. The method of intelligence transmission and reception utilizing in part a common amplifier and comprehending respectively the modulation and detection of signals which comprises generating oscillations locally for the dual purpose of modulation by the signals to be transmitted and for mixing with the received signal energy, amplifying the signals to be transmitted prior to the modulation of the local oscillations thereby, modulating the local oscillations with the outgoing amplified signals, receiving the incoming signal energy and mixing the locally generated oscillations therewith, and amplifying the received signal energy subsequent to the interaction of said local oscillations therewith and the detection thereof with the same amplifier executing the first-mentioned amplifying operation.

3. The method of intelligence transmission and reception utilizing in part a common amplifier which comprises generating oscillations locally for the dual purpose of modulation by the signals to be transmitted and for mixing with the received signal energy, amplifying the signals to be transmitted prior to the modulation of the local oscillations thereby, modulating the local oscillations with the outgoing amplified signals, receiving the incoming signal energy and mixing the locally generated oscillations therewith,

amplifying the resultant combination of the signal energy with local oscillations and deriving the received signal energy therefrom, and amplifying said last-mentioned signal energy with the same amplifier executing the first-mentioned amplifying operation.

4. In a radio communication system, an oscillator circuit, an antenna system coupled therewith, means for producing low frequency signalling energy for transmission, means for amplifying said energy .and for modulating the oscillator output therewith for transmission from said antenna system, a superheterodyne receiver circuit coupled with said antenna system comprising means including an audion tube and coupling circuits for combining the energy received from said antenna system with that of the local oscillator to obtain a signal-modulated intermediate frequency, means for detecting the combined energy of said last-mentioned frequency, means for passing the detected signals through said first-mentioned amplifying means, and a receiving device connected to the output circuit of said amplifying means.

5. In a radio communication system, an oscillator circuit, an antenna system coupled therewith, means for producing low frequency signalling energy for transmission, means for amplifying said energy and for modulating the oscillator output therewith for transmission from said antenna system, a superheterodyne receiver circuit coupled with said antenna system comprising means including an audion tube and coupling circuits for combining the energy received from said antenna system with that of the local oscillator to obtain a signal-modulated intermediate frequency, means for amplifying said intermediate frequency, audion means combined with said first-mentioned amplifying means for detecting the combined energy of said intermediate frequency and for amplifying the detected signals by said first mentioned amplifying means, and a receiver in the output circuit of said amplifying means.

6. In a radio communication system, an oscillator circuit, an antenna system coupled therewith, means for producing low-frequency signalling energy for transmission comprising a microphone connected in series with a battery and the primary winding of a transformer, means for amplifying said energy comprising an audion tube having the secondary winding of said transformer connected to the input of said tube,

means for modulating the oscillator output by said amplified low frequency energy, a superheterodyne receiver circuit coupled with said antenna system com-prising means including an audion tube and coupling circuits for combining the energy received from said antenna system with that of the local oscillator to obtain a signal-modulated intermediate frequency, means for amplifying said. intermediate frequency, audion means combined with said first-mentioned amplifying means for detecting the combined energy of said incoming frequency to derivethe incoming signals, means for directing the detected signals through another winding of said first-mentioned transformer operating as a primary winding with respect to said first-mentioned secondary winding to feed the detected signals to the input circuit of said first mentioned amplifying means for amplification thereby, and a receiving device in the output circuit of said amplifying means for the incoming signals.

'7.- In a radio communication system, an oscillator circuit, an antenna system coupled. therewith, means for producing low frequency signalling energy for transmission, comprising a microphone connected in series with a battery and the primary winding of a transformer, means for amplifying said energy comprising an audion tube having the secondary winding of said transformer connected to the input of said tube, means for modulating the oscillator output by said amplified low frequency energy, a superheterodyne receiver circuit coupled with said antenna system comprising means including an audion tube and coupling circuits for combining the energy received from said antenna system with that of the local oscillator to obtain a signalmodulated intermediate frequency, means for amplifying said intermediate frequency, audion means combined with said first-mentioned amplifying means for detecting the combined energy of said intermediate frequency to derive the incoming signals, connections for imposing the detected signals across a resistor, and connections from said resistor to the input of said firstmentioned amplifying means fOr amplification thereby, and a receiving device in the output circuit of said amplifying means for the incoming signals.

8. In a radio communication system, an oscillator circuit, an antenna system coupled therewith, a signal transmitter, means for amplifying the energy of said signal transmitter, and means for modulating the local oscillations therewith for transmission from said antenna system, a superheterodyzne receiver circuit coupled with said antenna system and said oscillator circuit for receiving incoming signal energy comprising a circuit of intermediate frequency, a final detecting stage for deriving the incoming signal energy, amplifying means for said lastmentioned energy, and a receiving device therefor, said first-mentioned and said last-mentioned amplifying means being common.

9. In a radio communication system, a tuned oscillator circuit containing inductance and capacity, an antenna connected at a potential loop thereof to said oscillator circuit, a signal transmitter, means for amplifying the energy of said signal transmitter, and means for modulating the local oscillations therewith for transmission from said antenna, a superheterodyne receiver circuit connected to said antenna and said oscillator circuit for receiving incoming signal energy comprising a circuit of intermediate frequency, a final detecting stage for deriving the incoming signal energy, amplifying means for said last-mentioned energy, and a receiving device therefor, said first-mentioned and said lastmentioned amplifying means being common.

10. In a radio communication system, an oscillator circuit, an antenna system coupled therewith, means for producing low frequency signalling energy for transmission, a plurality of ampiifying stages for amplifying said energy and means for modulating the oscillator output therewith for transmission from said antenna system, a superheterodyne receiver circuit coupled with said antenna system comprising means including an audion tube and coupling circuits for combining the energy received from said antenna system with that of the local oscillator to obtain a signal modulated intermediate frequency, means for detecting said intermediate frequency to derive the received signals, means for passing the detected signals through a lesser number of said first-mentioned amplifying stages than that through which the transmitted signalling energy passes, and a receiving device connected to the output circuit of one of the intermediate low frequency amplifying stages.

HERMANN MAYR.

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