US1740969A - Duplex transmission system - Google Patents

Description

Dec. 24, 1929. H. CHIREIX 1,740,969

DUPLEX TRANSMISSION SYSTEM Filed March 27. 1926 INVENTOR HENRI CHIREIX Patented Dec. 24, 1929 PATENT @FFEQ...

HENRI CHIREIX, OF PARIS, FRANCE DUPLEX TRANSMISSION SYSTEM Applicatien filed March 27, 1926, Serial No. 97,877, and in France August 12, 1925.

The present invention relates to radio communication apparatus by means of which two transmissions are sent out simultaneously by one and the same antenna.

It has already been suggested for this purpose to divide the antenna used for transmission into two parts, and to compensate at the base the exchange or transfer currents between said two parts by the aid of induc- 1o tive coupling of convenient kind between them. This scheme however, among other drawbacks, involves the inconvenience that, on account of the fact that but one half of the antenna is used for each transmission,

the aerial resistance is reduced.

The present invention has as its object to remedy the inconveniences in arrangements previously disclosed, by the simultaneous use for each of two transmissions of the entire 26 transmitting antenna. For this object two counterpoises are used provided in the neighborhood of each other and utilized to diminish in known manner the resistance of the aerialground circuit, and to play the part of catpacity in an auxiliary resonant circuit, with the end in view of imparting to the aerial two resonance periods. The invention furthermore provides a simple arrangement adapted to prevent the flow of current from one of 30': the alternators into the other.

The basic idea of the present invention will be better understood by reference to the accompanying drawing in which Fig. 1 is a circuit diagram of the arrangements, while Fig. 2 shows an equivalent diagram in which the capacities between the counterpoises and between the aerial and each of the counterpoises are indicated in the form of condensers.

Referring now to Fig. 1 an antenna is shown at A, having in its circuit a tuning inductance L connected to an intermediate point of a second inductance L whose terminals are connected to different portions of a double counterpoise D. The two portions of the latter are placed close enough together so that the required electrostatic capacity exists between them as explained below. Two 53 alternators are shown at- A and A designed to generate respectively the two frequencies f and f to be transmitted. The alternator A is connected to the antenna circuit by two inductive couplings M and M the former being in the antenna lead-in wire while the latter comprises the inductance L as one of its elements. The alternator A is connected to the antenna by similar inductive couplings M and M The equivalent circuit diagram shown in Fig. 2 makes it' clear that the system comprises, as a matter of fact, three circuits in electrostatic coupling relationship.

In this diagram the capacity between the two portions of the counterpoise is repre- 5 sented by C, and that between the aerial and each portion of the counterpoise by C The operation of this arrangement is as follows:

If self-inductance coil L is connected exactly at the middle of coil L on exciting self-inductance coil L by means of an oscillation generator, there is obtained a single resonance period which is independent of the value which C may be given, indeed, the latter may be varied within wide limits without altering the current flowing through the selfinductance coil L This goes to show that points A and B, by virtue of symmetry, are at the same potential. But if the self-inductance coil L is not connected exactly in the middle of coil L a very precise and definite value for condenser G will be found for which the current in coil L undergoes a decrease. This value of C corresponds to the condition where circuit L G is tuned to the transmitter. If, then, while not changing condenser C which is set to this value, the point of connection between coils L and L is varied, two frequencies will be obtained located upon either side of the original frequency. in the presence of which a certain current flows in the coil L Moreover the farther the tap or connection at coil L departs from the middle, the more these frequencies differ from the 5 mean frequency. Hence, the system has now two resonance frequencies. If, then, two equal couplings are provided at M M current will be found to flow in inductance coil Li only for one of the two frequencies before 100 obtained, say, the lower one. If, next, one of the couplings is reversed, no current is found to flow any more in self-inductance coil L for the lower frequency, but only for the higher frequency. This evidently goes to show that, for one sense of coupling of the coil M for instance, the reaction of the sender upon the system is zero. A current of this same frequency flowing through the system will furthermore not induce any electro-motive-force in the assembly of the two coils M and M In carrying the basic idea of the invention into practice, one of the two generators, A

for example, is connected with the antennaground circuit by means of an electromagnetic coupling M and with the auxiliary circuit through the agency of a second electromagnetic coupler M The generator A on the other hand, is united by electromagnetic couplings M and M, with the antennaground and the auxiliary circuit, respectively.

With proper connection of the four con- 2 pling means before-mentioned, it is thus possible to obtain and insure perfect independence of each of two transmissions, the frequencies of which correspond, respectively, to each of the two natural frequencies of oscillation of the radiating system. Contradistinct to what happens in an antenna divided into two parts, no interchange currents will be produced in the down-leads of the antennas; and these, as is well known, caused a considerable reduction in the effective height in the system previously disclosed.

The provision of the counterpoises is of the lowest possible cost, the potentials set up between the two parts of the counterpoise are not high, and this in turn means lower expense for insulation, while preserving the efficiency of operations at the same order of magnitude as in simplex working.

The fact that for each transmission the total capacitance of the wave radiating system is available contributes in large measure to an increase of the efi ectiveness of the system.

Having described my invention I claim:

1. A duplex transmission system comprising a single transmission conductor, means connected thereto for simultaneously imparting two resonant frequencies to the system ;and means for supplying energy to said system at each of said frequencies.

2. A duplex transmission system comprising a transmission conductor, means connected thereto to impart two resonant frequencies ito the system, an energizing means for said system and means for coupling it thereto to permit energization at one of said frequencies and prevent energization at the other of said frequencies, a second energizing means for 5 said system acting simultaneously with the' first and means for coupling it thereto to permit energization at the second of said frequencies and prevent energization at the first of said frequencies.

3. An antenna system comprising an antenna, an inductance having said antenna connected thereto intermediate its ends and a separate counterpoise connected to each end of said inductance, the capacity of these counterpoises forming with said inductance a resonant circuit.

" 4:. An antenna system comprising an antenna, two unequal inductance sections each having one end connected to'said antenna, a counterpoise connected to the other end of each of said inductance sections, said'counterpoises forming with both of said inductancesections a resonantcircuit.

5. A duplex transmission system comprising an antenna, an inductance having separate counterpoises connected to each end and forming therewith a resonant circuit, a lead connecting the antenna to an intermediate point of said inductance and two separate energizing means of difierent frequencies for energizing said system.

6. A duplex transmission system comprising an antenna, an inductance having a separate counterpoise connected to each end and forming therewith a resonant circuit, a lead connecting said antenna to an intermediate point of said inductance, two sources of high frequency current, inductive means for coupling each of said sources to said inductance, and means for coupling said sources to said lead.

7. A duplex transmission system comp'ris- HENRI GHIREIX.

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