US1958166A - Electrical signal receiver - Google Patents

Description

May 8, 1934.

T. LAURENT ELECTRICAL S IGNAL RECEIVER Filed Dec. 22, 1927 Patented May 8, 1934 PATENT OFFICE ELECTRICAL SIGNAL RECEIVER ,TorbernLaurent, Stockholm, Sweden, assignor to 'lelefonaktiebolaget L. M. Erlcson,v Stockholm, Sweden, a company of Sweden Application December 22, 1927, Serial No. 241,979 In Sweden January 4, 1927 9 Claims.

The invention relates to electrical signal receiv ers, particularly ringing signal receivers for use in connection with long distance telephone r lines provided with amplifying translators. 'In sending ringing signals, for instance calling and clearing signals, over such lines ringing currents of audio frequency are preferably'used as such currents may be passed through and amplified in the translators without any additional auxiliary means being required for that purpose. A general condition for the construction of such receivers is that the receiver shall operate reliably for ringing currents of a certain audio frequency while being unaffected by ordinary speech currents. The present invention has for its object to provide a signal receiver which fulfills this condition in a more perfect manner than has been possible heretofore and which is capable of being connected up between the two branches of the telephone line, directly or through a transformer, at any point desired.

The invention is based on the following principles. The signal receiver should operate for a current of a pure audio frequency which as to the value of the frequency and the incoming energy as well as its duration is confined within certain limits. With a view to securing a reliable and efficient service said limits should be rather spacious. Considering, however, that the frequencies occurring in speech may momentarily meet the said conditions for the ringing signal current, it will be necessary to take measures for preventing disturbances by the speech. This is realized according to the present invention by providing a blocking device responding to currents of audio frequency other than those covered by the ringing signals and adapted to put the Signal receiver in an inoperative condition. The operation of this blocking device is based on the fact that such tones of the speech which are most apt to affect the signal receiver, are never quite pure and, moreover, are of a very short duration in the course of ordinary speech. The fact last mentioned is taken advantage of by constructing said blockingdevice and the signal receiver so that the former will respond more quickly to the speech currents than the latter, whereas, after having once been made operative, it will be slow to regain its inoperative condition. I 50 The invention will be more closely described with reference to the accompanying drawing which illustrates three different circuit arrangements for a signal receiver.

Fig. 1 is a circuit diagram of the first embodiment.

Figs. 2 and 3 are corresponding circuit diagrams of the 2nd and the 3rd embodiment respectively.

In Figure 1, the circuit of the signal apparatus 1 is controlled by two relays 2, 3, included in the anode circuits of two rectifying valves 4, 5 69 respectively the grid circuits of which include the secondary windings of transformers 6, 7 and grid potential batteries 8, 9 respectively. The primary windings of saidtransformers are connected in series in the anode circuit of an amplifier valve 10 the grid and cathode of which are connected to the terminals 11, 12. By means of a battery 13 the grid of the valve 10 will obtain a potential adapted to cause the valveto operate only as an amplifier. A. battery 14. furnishes the current for the anode circuit. Bridged across the primary windings of the transformers 6, '7 are resonance shunts 15, 16 respectively, which are both tuned to the frequency of the signal current. The shunt is a potential shunt having an inductance and a capacity connected in parallel, whereas 16 is a current shunt having an inductance and a capacity connected in series. The transformer 7 and the appertaining circuits constitute a blocking device adapted 81? to make the receiver inoperative to currents of signal frequencies occurring in the speech.

The signal receiver is adapted to be connected up to the telephone line by the terminals l1, 12, being connected each to a branch of the line. $5 A signal current sent over the telephone line will then produce an alternating current potential in the secondary winding of the transformer 6, causing the relay 2 to operate and to close the circuit of the signal apparatus 1 at the W contact 1'7, whereas the relay 3 remains unoperated owing to the shunt 16 acting as a shortcircuit to the primary winding of the transformer 7 for currents of the signal frequency. For currents of other frequencies, for instance speech 5 currents, an alternating current potential will, however, be generated in the secondary winding of the transformer '7 so as to cause the relay 3 to open its contact 18, thus preventing the signal apparatus to be operated by momentarily 10% occurring speech currents of such frequencies that otherwise might be able to cause an operation of the signal apparatus. This operation of the blocking device depends upon the fact that speech currents are never of a pure frequency and said device will therefore practically operate for all speech currents including those which are most, apt to produce a false signal, provided the relay 3 is sufiiciently sensitive. The same result can be obtained quite apart from the said speech currents.

operation of the blocking device by making the relay 3 slow to release its armature so as to keep its armature attracted during the short intervals of the speech when currents of signal frequency or about that frequency occur. Evidently, said methods may be arranged to cooperate for the purpose'aimed at. It remains to consider the operation of the receiver at the very moment when a wave train of speech currents of signal frequencies enters the receiver and when both relays 2, 3 are still unoperated. At this moment the shunt 15 will at first act in known manner as a short-circuit, whereas the shunt 16 will act as a great resistance. As a consequence, the blocking device will enter into operation and will open the contact 18 in the signal circuit before the relay 2 attracts its armature, thus preventing false signal also in this particular case. Said action being due to the influence of the front of the incoming wave it will take place both for signal currents and for In case of signal frequencies the conditions are reversed after the incoming waves have developed normally in the shunts 15 and 16, so that the shunt 15 will then offer a great resistance to the currents, whereas the shunt 16 acts as a short-circuit thus producing the conditions first above described. The same result may, of course,. be obtained by making the relay 2 slow to attract its armature. An important feature of the blocking device is, therefore, that it shall be quick to enter into operation and relatively slow to regain inoperative condition.

The use of slow-acting relays 2, 3 may be unsuitable in some applications of the invention. This inconvenience is, however, overcome in the circuit arrangement shown in Figure 2. In this arrangement the circuit of the signal apparatus 1 is controlled by a single relay 19, included in the anode circuit of a valve 20. The grid circuit of said valve includes a grid leak 21 shunted by a condenser 22, and two batteries 23, .24, supplying a negative grid potential of such a value that the anode current is practically zero in the normal or in operative condition of the receiving device. Inserted in the secondary circuit of each transformer 6 and 7 is a glow lamp 25 and 26 respectively such as a neon lamp having builtir. resistances 27 and 2.8 respectively. Instead of neon lamps any discharge gap capable of independent discharge may be used. The secondary winding of the transformer 6 is connected at one end to the grid of the valve 20 through the neon lamp 25 and. a resistance 27 and at the other end to the positive pole of the neon lamp battery 23. The secondary winding of the transformer 7 is connected at one end to the grid of the valve 20 through the neon lamp 26 and resistance 28 and at the other end to the negative pole of another neon lamp battery 29. The voltage of the neon lamp batteries is not itself sufficient to cause glowing of the lamps, which therefore normally act as interruptions in the secondary circuits of the transformers. The voltage generated in the secondary circuits by the signal and speech currents will, however,

- cause the lamps to glow thereby establishing a conductive path through the lamps. Thus, when glowing, the lamp 25 will connect the grid of the valve 20 with the positive pole of the battery 23 and the upper plate of the condenser will obtain a positive charge, whereas the lamp 26 will supply a negative charge by connecting th grid with the negative pole of the battery 29. The blocking circuit will therefore, evidently, strive to neutralize the action of the signal current has ceased the condenser 22 will dischargev through the leak 21 and the valve 20 will be restored into its normal condition. v

If currents of other frequencies than the signal frequencies, for instance the speech currents, enter the signal receiver, the transformer 7 will come into operation causing the neon lamp 26 to glow whereby the upper plate of the condenser 22 will be charged negatively from the battery 29.

The valve 20 will consequently still allow no anode current to pass through it. If during this condition speech currents of such frequencies which are apt to cause operation of the signal apparatus, would enter the receiver, the glow lamp 25 would operate to supply a positive charge to the .condenser 22. It will be found, however, that in speech the negative charging is favoured to such an extent in preference to the positive one that the latterwill never predominate. This result is secured chiefly by the fact that the condenser 22 is relatively slow to discharge through the leak 21 and its negative charge w'll therefore be preserved till frequencies other can the signal frequencies again predominate. The condenser 22 should preferably be of such capacity so as to be charged by a small amount of energy, and the leak 21 should have such a resistance as to produce the slow action in the discharge of the condenser required for a reliable operation of the device. The action of a'.wave front is the same in this circuit arrangement as in that of Figure 1. Thus upon a wave train entering the receiver the blocking circuit will become operative more quickly than the signal circuit. The sluggishness of the signal circuit at this instance can be increased, if necessary by introducing an additional resistance in series with the glow lamp 25. The arrangement according to Figure 2 has the further advantage that disturbing currents, the energy of which is generally rather small, have no influence on the signal receiver at all as such feeble currents are unable to cause the gleamlamps to gleam.

In the modification shown in Figure 3 the potential generated in the secondary circuit of the transformer 6 influences directly the grid of the valve 20 instead of being used to charge the condenser 22 positively. It will be seen from the circuit diagram that the secondary winding of the transformer 6 is then connected up between the grid and the condenser 22, no neon lamp being used in the signal circuit. Otherwise the circuit arrangement is substantially the same as in Figure 2. The alternating currents generated in potentials in the transformer 8 that may occur. This arrangement oflers the possibility of using an. alternating current relay 19 tuned to the modulating frequency of .a modulated signal current,

for instance a 500-period current modulated with terns where a ringing signal is-sent over a wire connection as in the examples described above but may be used generally for wire or wireless systems. 'In both cases the ringing signal cur-- rents may be transmitted with or without the aid of a carrier wave.

Iclaim:

1; A receiving devicein an electric communication system comprising in combination a signalling circuit adapted to select signalling frequencies within a certain frequency range, a blocking circuit adapted to be passed by currents of other frequencies than the signalling frequencies, a valve device, signalling means controlled by'said valve device, means connecting the grid circuit of the valve device with the signalling circuit and means connecting the grid circuit of the valve with the blocking circuit in such a manner as to make the valve inoperative upon energization of the blocking circuit by such currents.

2. A receiving device in an electric communication system comprising in combination a signalling circuit adapted to select signalling frequencies within a certain frequency range, a

blocking circuit adapted to be passed by ourrents of other frequencies than the signalling and the blocking circuit in such a manner as to cause the condenser to be charged with different polarities by currents passed through the signalling circuit and the blocking circuit respectively.

3. A receiving device in an electric communication system comprising in combination a signalling circuit adapted to select signalling frequencies within a certain frequency range, a blocking circuit adapted-to be passed by currents of other frequencies than the signalling frequencies, rectifying discharge devices in said circuits, a valve device, signalling means controlled by said valve device, a condenser included in the grid circuit of the valve device, means connecting the condenser with the signalling circuit and the blocking circuit in such a manner as to cause the condenser to be charged with different polarities by currents passed. through the signallingcircuit and the blocking circuit respectively.

4. A receiving device as claimed in claim 2,

characterized by the said condenser being arranged to be charged by currents in the signalling circuit so as to make the valve operative.

5. A receiving device as claimed in claim 2, characterized by the said condenser being arranged to be charged by currents in the blocking circuit so as to make the valve inoperative.

6. A receiving device as claimed in claim 3, characterized by the condenser being charged through a glow lamp which is caused to glow by the action of the currents in the blocking cir-' cuit and the signal circuit respectively.

'7. A receiving device as claimed in claim 3, characterized by'the condenser and a leak resistance shunted thereto being included in both the signal circuit and the blocking .circuit, in each of which they are connected in series with a glow lamp and a glow lamp battery.

8. A receiving device as claimed in claim 3, in which a resistance is included in the signal circuit or the blocking circuit to retard the charging of the condenser.

9. A receiving device as claimed in claim 3, in which the discharge devices are adapted not to be brought to discharge by feeble currents such as disturbing currents. v

TORBERN LAURENT.

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