US2231958A

US2231958A - Carrier wave telephony system

Info

Publication number: US2231958A
Application number: US246456A
Authority: US
Inventors: Skillman Thomas Samuel
Original assignee: Hartford National Bank and Trust Co
Current assignee: Hartford National Bank and Trust Co
Priority date: 1937-12-27
Filing date: 1938-12-17
Publication date: 1941-02-18
Anticipated expiration: 1958-02-18

Description

Filed Dec. 17, 1958 ,DE/VOD.

s/GMXL Pacs/wp Patented Feb. 18, 1941 UNITED STATES PATENT OFFICE ommen WAVE 'rELErnoNY SYSTEM ford, Conn., as trustee Application December 17, 1938, Serial No. 246,456

InGei-many December 27, 1937 4 Claims.

My invention relates to carrier-wave telephony systems.

More particularly, my invention is concerned with systems of the type in which the transmit 5 ters and/or receivers of the individual channels are connected through iilters to a common transmission line, and in which signals are transmitted by transmission of a carrier-wave. which is suppressed lduring the transmissionjgof conversation, or of a signal current compriselwithin the conversation side-band.

The term signal currents is t0 be understood to include broadly any signal currents which are produced in the transmitter and used to control any signal circuit on the receiver side. Thus, this term also includes the selective impulses used in automatic systems,

In systems of the above type it is the usual practice to feed the signal currents in the transmitter to the transmission conductor before feeding them to the filter associated with the corresponding channel, while in the receiver the signal circuit for each channel is connected behind the lter associated with this channel. Thus, the signal currents passed through both the lters on the transmitter side and the lters on the receiver side. However, to avoid4 overlapping conversations the filters are always so proportioned that for transmitting communications they transmit substantially only the conversation side-band used in the channel concerned. The attenuation at the carrier frequency is then appreciable and asia result the signal currents are always weakened to a considerable extent by their passage through the filters. Moreover this attenuation may vary considerable with temperature changes. With regard to these variations of attenuation the signal receiver must be constructed to operate at different strength of the received signal currents and this involves diiiiculties. To avoid defective control of the signal circuit it is necessary to provide signal currents of large amplitude, and be cause of the reduction of the amplitudes in the iilters, it has been necessary to produce in the transmitter signal currents of extremely high amplitudes, which increased the cost of the transmitter. V

'I'he object of my invention is to overcome the above difiiculty and to allow a decrease in the amplitudes of the signal currents produced in the transmitter, while at the same time obtaining a low attenuation of the signal currents and a reliable operation of the signal circuit.

In accordance with the invention, I pass the signal currents directly to the transmission line,

or pass them through only a portion of the lters, and as a result avoid any substantial weakening of these currents.

In one embodiment of the invention I employ lters comprising two sections, of which the section connected to the transmission line slightly attenuates the signal current frequency, and the other section produces a high attenuation of this frequency. Furthermore, I preferably so design the filter sections that they have high input impedances at the connecting point of the signal receiver, and thus make it unnecessary to use matching transformers for connecting the signal receiver.

In order that the invention may be clearly understood and readily carried into eiect, I shall describe the same in more detail with referencer to the accompanying drawing, in which;

Figure l is a schematic diagram of a portion of a carrier-wave system embodying the invention, and

Fig. 2 is a schematic diagram of the filters of Figure 1.

In Figure l the speech currents are fed through conductors I and 2 to a bridge modulator 3, and modulate a carrier-wave produced by an oscillator il, the carrier-wave at the same time being suppressed. The output voltage of modulator 3 passes through a band-pass filter 5 to a trans mission line 8 connected to collecting buses 9 and I0 to which the transmitters of other channels (not shown) are connected.

The lter 5, which comprises two sections 6 and 'I connected through conductors II and I2, passes only one of the two side-bands of the modulated wave produced in modulator 3. Section 6 may be so designed that it highly attenuates the 'carrier frequency together with the speech frequencies lying below and slightly above the carrierfrequency section `I may be so designed to offer a low and constant attenuation to the signal currents, which in the present case are of carrier frequency.

The signal currents are supplied to conductors I I and I2, and for this purpose there is provided a relay I3 controlled by a circuit comprising a switch I4 and battery I5, and having two single-throw normally-open arms I 6 and Il. Arm I6 has its heel connected to one terminal of oscillator i and is adapted to engage a fixed contact I9 connected through a resistance I8 to conductor I2, and arm II has its heel connected to the other terminal of oscillator 4 and is adapted to engage a xed contact 20 directly connected to conductor il. Thus, closure of switch I4 causes the carrier-wave produced by oscillator 4 to be applied to conductors and l2 and hence through filter section 1 to line 3.

It will be noted that the signal currents do not pass through filter section 6, which, as stated,

brings out considerable attenuation of the carrierwave. Filter section 1, causes only a slight attenuation of the carrier-wave with the result that the signal ycurrent is not weakened to any appreciable degree by its passage through filter 5.

Instead of being connected to conductors and I2, i. e., between two sections of the filter, the contacts I9 and 20 can be connected to buses 9 and |0 respectively.

'I'he transmission line 8 is connected to the buses 2| and 22 to which receiver systems for several other channels (not shown) may be connected. As shown, the receiver system comprises a bandpass lter 23 connected to buses 2| and 22 and comprising two sections 24 an'd 25 connected through conductors 26 and 21 and corresponding to sections 1 and 6 respectively of the transmitter system. The output of section 25 is fed to a demodulator 28 whose output, after being rectified, is passed through conductors 29 to the subscriber line.

Connected to conductors 26 and 21 is a signal receiver, which, however, could be connected directly to buses 2| and22. The signal currents in conductors 26 and 21 are supplied through a matching transformer 30 to the grid circuit of a triode 3| whose plate circuit includes a band-pass filter 32 which is tuned sharply to the carrierwave. The output voltage of lter 32 is rectified by a detector 33 whose output controls the actuating circuit of a relay 34 having a single-pole normally-open arm 35 which controls a signal circuit including a battery 36 anda bell 31.

A suitable construction of the lter 23 of Figure 1 is shown in Figure 2 in which the lter section 25 comprises two inductances 38 and 40 and a condenser 39 connected in series with conductor 26, and an inductance 4| and a condenser 42 connected in series between conductor 21 and a point between condenser 39 and inductance 40. The illter section 24 comprises a condenser 43 and an inductance 44 connected in series with conductor 26 and a condenser 45 connected between conductor 21 and a point between condenser 43 and inductance 44. The two sections are preferably so designed that there is a high impedance between sections. Because of this the matching transformer 30 of Figure 1 can be replaced by the simple coupling resistance 46 of Figure 2.

'Ihe filter 5 of Figure 1 is constructed similarly to that of Figure 2 with sections 6 and 1 thereof corresponding to sections 25 and 24 respectively of Figure 2.

While I have described my invention with reference to specific applications and examples, I do not wish to be limited thereto, but desire the appended claims to be construed as broadly as is permissible in view of the prior art.

What I claim is:

1. In a carrier-wave system for transmitting intelligence from a modulator located at a transmitter station to a demodulator located at a receiver station by means of suppressed carrier modulated waves, a transmission line interconnecting said transmitter station and receiver station, a band-pass filter connected between said modulator and said transmitting line, a band-pass filter connected between said demodulator and said transmission line, both of said lters transmitting only one of the two side bands generated at the modulator, means for transmitting additional signals by the transmission of the carrier wave which is suppressed during the transmission of the intelligence, and means for transmitting said additional signals through only a portion of one of said lters.

2. In a carrier-wave system for transmitting intelligence from a modulator located at a transmitter station to a demodulator located at a receiver station by means of suppressed carrier modulated waves, a transmission line interconnecting said transmitter station and receiver station, a band-pass lter connected between said modulator and said transmitting line, a band-pass lter connected between said demodulator and said transmission line, both of said filters transmitting only one of the two side bands generated at the modulator, means for transmitting additional signals by the transmission of the carrier wave which is suppressed during the transmission of the intelligence, said means including a source of the additional signals, and means for connecting said source directly to said transmission line.

3. In a carrier-wave system for transmitting intelligence from a modulator located at a transmitter station to a demodulator located at a receiver station by means of suppressed carrier modulated waves, a transmission line interconnecting said transmitter station and receiver station, a band-pass filter connected between said modulator and said transmitting line, a band-pass filter connected between said demodulator and said transmission line, both of said lters transmitting only one of the two side bands generated at the modulator, means for transmitting additional signals by the transmission of the carrier wave which is suppressed during the transmission of the intelligence, one of said filters comprising a section connected to said transmission line and slightly attenuating the additional signals and a second section highly attenuating the additional signals, and means for transmitting said additional signals through only the first section of said fllter.

4. In a carrier-wave system for transmitting intelligence from a modulator located at a transmitter station to a demodulator located at a receiver station by means of suppressed carrier modulated waves, a transmission line interconnecting said transmitter station and receiver station, a band-pass filter connected between said modulator and said transmitting line, a band-pass lter connected between said demodulator and said transmission line, both of said lters transmitting only one of the two side bands generated at the modulator, means for transmitting additional signals by the transmission of the carrier wave which is suppressed during the transmission of the intelligence, one of said filters comprising a section connected to the transmitting line and slightly attenuating the additional signals and a second section highly attenuating the additional signals, and means to pass said additional signals' through only the first section of said filter, including a signal circuit connected to a point between said sections, said lter sections exhibiting a high input impedance at said point.

THOMAS SAMUEL SKILIMAN.