US2073451A - Transmission system - Google Patents

Description

March 9, 1937. R B. LORD 2,073,451

TRANSMISSION SYSTEM Filed Jan. 2; I935 INVENTOR R. B. LORD A T TORNEV Patented Mar. 9, 1937 TRANSMISSION SYSTEM Reginald B. Lord, Los Angeles, Calif., assignor, by

mesne assignments, tqWestern Electric Gom- T pany Incorporated, a corporation of New York UNITED STATESVPATENT OFFICE Application January 2, 1985, Serial N8. 87

In Great Britain June 6, 1934 I 13 Claims.

l1) plying separate signal currents independently to' the respective devices and, at the same time, preventing one device from responding to the signal current intended for the other device.

For convenience of description, the invention 1,; has been embodied in a film sound recording system. The invention is not thereby limited to film sound recording, but' may be embodied in any desired signal transmission system such as telegraph, telephone, radio, television, telephotog- 2O raphy, telemetering and similar systems.

;In film sound recording systems in which a record of varying density is produced by a light beam modulated by a pair of shutters or ribbons, ,due to the finite height of the recording beam, certain inaccuracies are produced in the record.

It has recently been proposed to actuate the shutters or ribbonsindependently with power from separate channels connected to the source ofsignals, A phase shifting network is incorporated in one channel and delays the signal current supplied to one shutter or ribbon with respect to the signal current supplied to another shutter or ribbon. In such a recording system, the direct signal current and the delayed signal current must be kept separate and each permitted to actuate only one of the shutters or ribbons.

- Recording systems are also known in which the position or spacing of the recording device is controlled by a slowly changing unidirectional biasing current varying with some function of the signal amplitudes, thus producing a reduction in the film noise produced during reproduction. The present invention permits the biasing current from a noise reduction control circuit to be applied to a phase shift recording circuit in such manner that the unidirectional current from the noise reduction circuit does not changethe electrical constants of the phase shift channel or the direct signal channel. In the drawing: 7 I Fig. 1 is a simplified diagrammatic sketch of the invention; 7 l

Fig. 2 is a simplified diagrammatic sketch of the invention applied to transformer terminated signalchannels; g

Fig. 3 is a modification of Fig. 2; I

Fig. 4shows diagrammatically a phase shift noise reduction sound recording system embodying the circuit of Fig. 2; I

. Fig. 5 shows a modified system embodying the circuit of Fig. 3. I

In Fig. 1, a signal responsive device 5, and an element 28 having the same impedance as the device 5.are connected in serial relationship across channel. A pair of elements 36, 31, having equal impedances arevalsoconnected in serial relationship across the terminals 45, 46 of the signal transmitting channel. Signal currents will flow through the device 5 and the element 20, and, as

the. terminals 45, 46 of a signal transmitting v these are of equal impedance, they will cause equal potential losses, thus the junction,,l9 will havea potential, midway between the potentials of the terminals of the signal transmitting channels. Similar1y,.signal currents will flow through the elements31 and 36, andas theseelements are of equal impedance, the wire 38 will be at a potential midway between the potentials of the terminals of the signal transmitting channels. Thus the signal currents do not produce any difierence of potential between the junction l9 and thewire 38. The junctionJB and the wire 38 are thus in conjugate relationship with the terminalsAS, 46 of the signal transmitting channel; 1

Similarly, in Fig. 1, a signalresponsive device 6 and. an element 38 having the same impedance as the device 6 are connected in serial relationship across the terminals 41, 48 of a secondsignal transmitting channeL- A pair of elements34, 35 having equal impedances are also connected in serial relationship across the terminals 41, 48 of the second signal transmitting channel. In this case, the signal currents from the second signal transmitting channel do not produce any difierenceof potential between the junction l9 and the wire 33. Again the junction .l9 and wire 33 are in conjugate relationship with the. terminals 41, 48 of the channel.

- As the signal transmitting channels are only joined at the junction 19, signal currents from one channel will, not fiow through the device.

which is responsive tdthe sigrialsfrom, the other channel. z p

A control or biasing circuit may be attached to the, wires 33 and 38. As the; signal currents do not produce any potential. difference between i Current from the control circuit will flow through element 31 and signal responsive device 5 in series, thus biasing the device 5. Current will also flow through elements 36 and 20 in serial relationship. But, element 31 and device 5 have the same total impedance as elements 36 and 28. The control current thus divides equally in the two paths. As elements 36 and 31 are of equal impedance and traversed by equal currents, the potential drops in the elements are equal. Thus the terminals: 45, 46 of the signal transmitting channel are at equal potentials with respect to the biasing current, and. no biasing current will flow in the signal transmitting channel.

Similarly, the current from the control circuit will flow equally in the element 30 and. the device 6, thus biasing the device 6. And, as elements 34 and 35 are of equal impedance, the terminals 41, 48 of the second signal transmitting channel are at equal potentials and no biasing current will flow in the second signal transmitting channel.

Due to the balanced condition of the two bridges thus formed either junction of the first bridge may be connected to either junction of the second bridge, and the control circuit connected to the remaining two junctions. Also,

the equal elements may be interchanged in position, for example, the positions of device 5 and element 20 may be interchanged, and the positions of device 6 and element 30 may be interchanged.

In Fig. 2, the signal transmitting channels respectively terminate in the primary windings of the transformers II and 28. The secondary windings of the transformers l1 and 28 are respectively connected to the signal transmitting channel terminals. As before explained, current from the control or biasing circuit will not flow in the secondary windings of the transformers I7 and 28, thus preventing the control currents from magnetizing the cores of transformers l1 and 28.

In Fig. 3, the secondary windings of transformers l1 and 28 are accurately tapped in the center, and the taps connected to wires .38 and 33. In this case, the impedances of the halves of the secondary winding of transformer take the place of the elements 36 and 31 in Fig. 1. Similarly, the impedances of the halves of the secondary winding of transformer 28 take the place of the elements 34 and 35 in Fig. 1.

In Fig. 4, light from a source I is focused by the lens system 2 on the aligned orifices 3 pierced in the pole-faces of the magnet 4. A .pair of shutters or ribbons 5, 6 define the height of the beam of light transmitted through the orifices 3. An image of the slit thus formed is focused by the lens 1 on the film 8, traversed in the usual manner from the reel 9 to the reel It).

An opaque plate ll, pierced by a suitable orifice, protects the film from undesired light. The shutter 5 is placed vertically above the shutter 6 in a plane parallel to the plane of the film 8. When signal currents flow in the shutters or ribbons 5 or 6, the magnetic fields produced by the currents will react with the field of the magnet 4 to produce an oscillation of the shutters 5 or 6 having a component of motion in the direction of the motion of the film 8. If identical currents simultaneously fiow in both the shutters or ribbons 5 and 6, the impressions produced on the film 8 will not coincide in position, due to the finite height of the recording slit defined by the shutters or ribbons 5 and 6. The record produced is thus not perfect, and a loss of the high frequencies results.

While for convenience a specific form of light valve has been described, the invention is in no way limited to this form of light valve but is applicable to many other forms. The shutters which control the recording beam may be mounted upon stretched ribbons which conduct the signal currents, or they may be mounted upon a resilient spider driven by a coil traversed by the signal currents. Or, the shutter may be mounted upon or formed of a stretched magnetic ribbon with the signal currents impressed on a coil mounted upon the pole pieces of the magnet.

A microphone I2, with amplifiers l3, l4 forms a source of signal currents supplied to the recording bus-bars l5, l6. Any other suitable source of signal currents may be used and the invention is in no way limited to the source disclosed.

Signal currents flow from the bus-bars |5, |6 through transformer wire 39, to the shutter or ribbon 5, thence through wire l9 and resistor 20 to transformer causing the shutter or ribbon 5 to oscillate in accordance with the signal currents.

Signal currents also flow from the bus-bars I5,

l6 through the phase shift network formed of the series resistor 2|, series inductors 22 and 23, series capacitor 24 and the shunt capacitors 25, 26 and 2! through transformer 28, wire 29, to the shutter or ribbon 6, thence through wire I9 and. resistor 30 to transformer 28 causing the shutter or ribbon 6 to oscillate in accordance with the currents. The phase shift network delays the current in this channel with respect to the current in the channel to the shutter or ribbon 5 for a time interval related to the time required for an element of the film 8 to pass through the recording light beam.

Current from a suitable source, such as the battery 3|, flows through wire 33 to the junction of the equal resistors 34, 35. One part of the current fiows through resistors 34, 3|], 20, 36 wire 38, and resistor 32 to battery 3|. Another part flows through resistor 35, wire 29, shutters or ribbons 6 and 5, wire 33, resistor 31, wire 38, resistor 2 to battery 3|. If resistor 34 is equal in resistance to resistor 35, no current will flow in the secondary winding of transformer 28, thus preventing the core of transformer 28 from becoming magnetized and changing the electrical constants of the phase shift channel. Similarly, the resistors 36 and 31 prevent the core of transformer H from becoming magnetized. Also, if the resistances of the resistors 20 and 33 are respectively equal to the resistances of the shutters or ribbons 5 and 6, no current from the battery 3| will flow in the wire IS. The current fiowing in the shutters or ribbons 5 and 6 will draw the shutters or ribbons 5 and 6 nearer together, thus reducing the film noise in the known manner.

Signal currents from the bus-bars |5, |6, suitably amplified in the amplifier 40, is transmitted through transformer 4| to the full wave rectifier 42 and charge the capacitor 43. The charge on the capacitor 43 leaks through the resistance 44' and decreases the efiect of the current from the battery 3| on the recording device, permitting the spacing of the shutters or ribbons 5 and 6 to increase as the amplitude of the signals increases.

In Fig. 5, the secondary windings oi the transformers "H and 2 8are ac'curately tapped at the "center-point. Inf this case, the current from wire 33 fiows equally through the two halves of the secondary winding of transformer 2 8, but in opposite directions soth'at' the magnetic effects of the two currents balance each other and no magnetization of the core of the transformer is produced; "Similarly, the current-to wiref38 flows equally, through the two halves of the secondary windingcf transformer l1 and no magnetization of the core is produced. In this case, the resistances 34, 35, 36, 31 are not necessary and may be omitted.

What is claimed is:

1. In combination, a recording channel, a recording device and an element of equal impedance connected in serial relationship to the terminals of said channel, a pair of equal impedance elements also connected in serial relationship to the terminals of said channel, the junction of said device and said first element and the junction of said equal impedances being in conjugate relationship with the terminals of said channel, a second recording channel, a second recording device and a second element of equal impedence connected in serial relationship to the terminals of said second channel, a second pair of equal impedance elements also connected in serial relationship to the terminals of said second channel, the junction of said second device and said second element and the junction of said second pair of elements being in conjugate relationship with the terminals of said second channel, one junction associated with said first channel being connected to a junction associated with said second channel, and a control circuit connected to the other junctions.

2. The combination in claim 1 in which sai recording devices are incorporated in one unitary structure.

3. The combination in claim 1 in which said recording channels carry currents from a common source, one channel comprising a phase shifting network.

4. The combination in claim 1 in which said control circuit supplies a unidirectional current varying with some function of the currents recorded.

5. The combination in claim 1 in which said recording devices are stretched conducting ribbons immersed in a common magnetic field.

6. In combination, a recording channel, a transformer having its primary winding connected to said channel, a pair of equal impedance elements forming a secondary winding of said transformer, a recording device and an element of equal impedance connected in serial relationship to the terminals of said secondary winding, the junction of said device and said element and the junction of said equal elements being in conjugate relationship to the secondary terminals of said transformer, a second recording channel, a second recording device and a second element of equal impedance connected in serial relationship to the terminals of said second channel, a second pair of equal impedance elements also connected in serial relationship to the terminals of said second channel, the junction of said second device and said second element and the junction of said second pair of elements being in conjugate relationship to the terminals of said second channel, one junction associated with said first 75 channel being connected to one junction associated withsaid second channel and a control -arena-teammatethe other ut-1mm;-

7,: The combination in claim 6 in -which said recording ev ces-ar incorporated in" one em r I g, gm a' cornmon -magnetic field.

The combination in claim 6 in which said recording currents from "a common source'onechannel comprising'a phase shifting network.

10. The combination in claim 6 in which said control circuit supplies a unidirectional current varying with some function of the currents recorded.

11. In a transmission system, in combination, a signal transmitting channel, a signal responsive device and an element of equal impedance connected in serial relationship to the terminals of said channel, a pair of equal impedance elements also connected in serial relationship to the terminals of said channel, the junction of said device and said first element and the junction of said equal elements forming the free terminals of a balanced bridge, a second signal transmitting channel, a second signal responsive device and a second element of equal impedance connected in serial relationship to the terminals of said channel, a pair of equal impedance elements also connected in serial relationship to the terminals of said channeLthe junction of said second device and said second element and the junction of said second pair of equal impedances forming the free terminals of a second balanced bridge, one free terminal of said first bridge being connected to a free terminal of said second bridge, and a control channel connected to the other free terminals of both bridges.

12. In a transmission system, in combination, a signal transmitting channel, a transformer having its primary winding connected to said channel, a pair of equal impedance elements forming a secondary winding of said transformer, a signal responsive device and an element of equal impedance connected in serial relationship to the terminals of said secondary winding, the junction of said device and said element and the junction of said equal elements being in conjugate relationship with the terminals of said secondary winding, a second signal transmitting channel, a second signal responsive device and a second element of equal impedance connected in serial relationship to the terminals of said channel,.a pair of equal impedance elements also connected in serial relationship to the terminals of said channel, the junction of said second device and saidsecond element and the junction of said equal impedances being in conjugate relationship with the terminals of said second channel, onejunction of said first channel being connected to one junction of said second channel, and a control channel connected to the other junctions.

13.In a transmission system, in combination, a signal transmitting channel, a transformer having its primary winding connected to said channel, a pair of equal impedance elements forming a secondary winding of said transformer, a signal responsive device and an element of equal impedance connected in serial relationship to the terminals of said secondary winding, the junction of-said device and said element and the 'mbina ion' clai'rn 6 in which said reref-stretched conducting ribbons 10 serial relationship to the terminals of the secondary winding of said second transformer, the junction of said second device and said second element, and the junction of said second pair of elements being in conjugate relationship with the terminals of the secondary winding of said second transformer, one junction of said first channel being connected to one junction of said second channel and a control channel connected to the other junctions.

REGINALD B. LORD.

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