US2476880A - Single side-band system - Google Patents

Description

July 19, 1949. B. E. LENEHAN SINGLE SIDE-BAND SYSTEM Filed Oct. 20, 1945 Receiver INVENTOR ATTORNEY Bernard ELen/mn ml. J/

Fig. 2.

Amplifier WITNESSES y 042/ Osczllai'or Patented July 19, I949 SINGLE SIDE-BAND SYSTEM Bernard E. Lenehan, Bloomfield, N. J., assignor to Westinghouse Electric Corporation,

East

Pittsburgh, Pa., a corporation of Pennsylvania Application October 20, 1945, Serial No. 623,594

24 Claims.

This invention relates to systems for transmitting signals, and it has particular relation to single sideband systems.

The advantages of single side-bandtransmission are well known in the art. For example, reference may be made to the Radio Engineering Handbook, Third Edition, by Keith Henney. 1941, pages 552 and 553. This handbook is published by the McGraw-Hill Book Company of New York city. However, the size, cost and com plexity of the equipment required for single sideband systems designedin accordance with the prior art have discouraged extensive commercial utilization of the system.

In accordance with the invention, an improved and simplified single side-band system is provided for transmitting signals. Transmission may be efiected over any desired channel. For example, the transmission may be effected by the pro-pogation of radiation through space, that is, radio, or it may be effected over conductors.

A signal transmitted by systems embodying the invention may be employed for any desired function. For example, the signals may be employed for communication purposes, for relaying purposes, for telemetering purposes or for supervisory control of any desired equipment.

The invention contemplates the provision of a polyphase carrier wherein the phase components of the carrier are displaced by a substantial angle. In addition, the signal-to-be-transmitted is also produced in polyphase form wherein the phase components are displaced by substantially the same angle present between the phase components of the carrier. Each component of the signal to be transmitted modulates a separate one of the carrier components in a suitable modulator.

Preferably the modulator is of the balanced type in order to suppress the carrier component. The outputs of the two modulators consist respectively of the sum and difference of the upper and lower side bands formed by the modulation of the carrier. By suitably adding or subtracting the outputs of the two modulators, either the upper or the lower side band alone may be produced.

In systems embodying the invention, three major problems are present. The balanced modulator must be adequately balanced in order to suppress substantially the carrier supplied thereto. In addition, the outputs of the two modulators must be properly related to effect substantial cancellation of one of the side-bands produced thereby. Finally, adequate equipment must be provided for producing the phase components of the carrier and signal. If phase shifters are through appropriate rectifier-s in the modulator..

CancellatiOn of one of the side-bands produced by the two modulators in systems embodying the invention is facilitated by the provision of adjustments for controlling the amplitudes of the outputs derived from the two modulators.

In order to provide polyphase carrier and signal quantities, phase shifters are hereinafter illustrated and described which maintain the amplitude and phase displacement of related components substantially constant over the entire frequency range desired. The phase shifters are of the static type employing only resistors, capacitors and inductance elements.

It is, therefore, an object of the invention to provide an improved system for transmitting signals.

It is a further object oi the invention to provide an improved single side-hand transmitter.

It is a further object of the invention to provide a single side band transmitter employing barrierlayer modulators.

It is also an object of the invention to provide means for adjusting the impedance distribution of a barrier-layer modulator.

It is an additional object of the invention to provide means for adjusting the extent of sup-,

pression of a carrier in a modulator.

It is a still further object of the invention to provide means for adjusting the extent of cancellation of a side band in a phase-rotation, single-side-band transmitter.

Additional objects of the invention will be apparent from the following discussion taken in conjunction with the accompanying drawing in which:

Figure 1 is a schematic view or a system embodying the invention.

Fig. 2 is a schematic view showing a modified output unit suitable for the system of Fig. 1, and

Fig. 3 is a block diagram of a receiver suitable for the system illustrated in Fig. 1.

Referring to the drawing, Fig. 1 shows equipment located at two spaced stations A and B for the transmission and reception of signals between the two stations. Such signals may be transmitted in any suitable manner. However, for the purpose of discussion, it will be assumed that the stations A and B are connected by electric power lines comprising conductors LI and L2 which are to be employed for guiding signals between the two stations. A system of this type is commonly referred to as a power-line carrier system.

7 component Ee cos 211st and the signal component transformer 3 to a phase shifter 3. The phase shifter 5 is designed to supply to the primary windings IA and 9A of two transformers 1 and 9 two carrier phase-components which are displaced from each other by a substantial angle. For example, this angle may be in the range of 60 to 90". For optimum performance, however, it is desirable that the angle of displacement be substantially 90. For example, the phase shifter 5 may be designed to apply to the primary winding 1A of the transformer 1 a quantity represented by the expression Ec cos 21kt, wherein Ec is a constant amplitude factor, fc represents the car rier frequency. and t represents time. The phase or for telemetering, or for supervisory control purposes, or it may be a voice signal. For present purposes, it will be assumed that a voice signal is provided by means of a microphone IS, the output of which may be amplified, if necessary, by means of an amplifier H. The output of the amplifier I! is coupled through a transformer l9 to a phase shifter 2|. This phase shifter is designed to produce two signal components which are displaced in phase by substantially the same angle of displacement present between the two carrier components supplied by the transformers,

l and 9.

For example, let it be assumed that a signal having a frequency '1' is supplied through the transformer I9 to the phase shifter 2|. The

phase shifter then may be designed to provide an output between the conductors 23 and 25 which is represented by the expression -E. sin 21rfst,

wherein Es represents an amplitude factor. In addition, the phase shifter provides an output between the conductors 21 and 26 which may be represented by the expression E- cos 21kt. By

E cos 21m. Consequently. if the modulator I is of the balanced type, the output thereof may be represented by the expression (E0005 211st) (E- cos 214.0. This expression represents the sum of the two side bands produced by the modulator and may be represented by the expression In a similar manner the modulator l3 has applied thereto the two components represented by the expressions Ec sin 21kt and E. sin 211st. If the modulator I3 is of the balanced type. its output may be represented by the expression The output of the modulator II is applied to a load resistor 29 through a coupling transformer 3|. Similarly, the output of the modulator I3 is applied to a load resistor 33 through a transformer 35. I

From the foregoing discussion, it is clear that the voltage drops across the resistors 29 and 33 represent respectively the sum and difference of the upper and lower side-bands produced by the modulators I! and I 3. Consequently, by adding these voltage drops, the resultant voltage represents the lower side-band. By subtracting the two voltage drops the resultantvoltage represents the upper side-band.

The resultant voltage is applied to a suitable amplifier 31. To this end, a conductor 39 is connected to the resistors 29 and 33 through adjustable taps 4| and 43. Each tap and its associated resistor may constitute a potentiometer. By suitable adjustment of the taps, the portions of the voltage drops across the resistors 29 and 33 which are utilized may be adjusted to eliminate substantially one of the side-bands. This is desirable for the reason that the circuits associated with the modulators II and I! may not be exactly similar.

One terminal of the resistor 33 is connected to ground through a conductor 45 and the conductor 25. One terminal of the resistor 29 is connected through a conductor 41 to the amplifier 31. The output of the amplifier 3'I,may be coupled in any suitable-manner to the conductors LI and L2, as through capacitors 49 and 5|.

From the preceding discussion, it is clear that a single side-band signal is applied to the conductors LI and L2 through the capacitors 49 and 5|. This signal may be picked up at the station B in any suitable manner. As illustrated in Fig. 1, a receiver 93 suitable for receiving single side-band signals is coupled to the conductors LI and L2 at the station B through phase shifter corresponding to the capacitor 59 and the resistor 8| would produce substantially a 90 phase displacement between the components supplied to the primary windings IA and 9A with substantially equal amplitudes for only one frequency-of the oscillator I.

It is desirable that the phase shifter be ca-v pable of producing a similar phase shift and maintaining substantially constant amplitude of the components for all frequencies for which the oscillator may be adjusted. As previously pointed out, the oscillator may be designed to operate at any frequency within the range of 50 to 150 kilocycles per second. In order to make the phase shifter 5 effective over this entire range of frequency, a pair of inductance coils 53 and 55 are provided which are mutually coupled. By reference to Fig. 1, it will be noted that the coil 53 is-connected in series with the capacitor 58 and the resistor 6| across the secondary winding of the transformer 3.

It is well known in the art that the voltage drops across inductance coils and capacitors vary as functions of frequency in opposite directions. Since the coils 63 and 65 are mutually coupled, a voltage is induced in the coil 65 which also varies as a function of frequency. However, the voltage across the coil 65 is substantially in phase with the voltage across the capacitor 59. Since the amplitudes of the voltages across the coil 65 and capacitor 59 vary in opposite directions as the frequency of the oscillator l is changed, it may be observed that the components of the phase shifter 5 may be proportioned to. maintain the resultant voltage across the coil 65 and the capacitor 59 substantially constant over a small i range of frequency, such as a range of 50 to 150 kilocycles per second. Since the primary winding 1A is connected for energization in accordance with this resultant voltage, the voltage applied to this primary winding 7A is rendered substantially constant over the desired frequencyrange.

Further improvement in the performance of the phase shifter 5 is efiected by making the internal impedances of the two output circuits of the phase shifter substantially equal. To this end, a resistor 6'! is provided which is substantially equal in value to the value of the resistor 6|. Also a capacitor 69 and an inductance coil 1| are located in the circuit energized by the voltage across the resistor 6|. The capacitor 69 and the inductance coil H correspond respectiveiy in value to the capacitor 59 and the inv ductance introduced by the inductance coil 65.

As representative of suitable values for the components of the phase shifter 5, the following table is presented:

Capacitor 59 microfarad .01

Capacitor 69 do .01 Resistor 6| .r ohms 400 Resistor 61 do r 400 Mutual coupling between coils 63 and 65 henry .0004 Coil ll do .0004

These values are suitable for a frequency range of 50 to 150 kilocycles per second and maintain For example, in telephone conversation, it is desirable to have a frequency range of the order of 250 to 4,000 cycles per second. For such a range, the phase shifter 2| must handle an upper limit frequency which is approximately 16 times a the lower limit frequency.

Certain components of the phase shifter 2| correspond to components of the phase shifter 5. For example, the phase shifter 2| includes inductance coils I3, 15 and I6, capacitors l1 and 19 and resistors 8| and 83 which correspond respectively to the coils 63, 65, and 1|, the'capacitors 59 and 69 and the resistors 6| and 61 of the phase shifter 5. The.performances of the corresponding components are similar in the two circuits, but it is to be understood that the values thereof are selected in accordance with the frequencies to be handled thereby. It may .be pointed out that the capacitance of the capacitor 59 and the inductance introduced by the coil 53 across the secondary winding of the transformer 3 preferably should be resonated approximately to the geometrical mean of the frequency range which is to be applied to the phase shifter. A similar comment holds for the capacitor I1 and 1 the coil 13 of the phase shifter 2|.

all)

If only the components thus far mentioned for the phase shifter 2| were employed, the amplitude of the voltage applied between the conductors 23 and 25 would be equal to the voltage applied between the conductors 21 and 25 for only two frequencies. If the amplitudes 'of these voltages were plotted as a function of frequency,

the curves would intersect at two points. Because of the difference in amplitudes of the voltages within operating range, the cancellation of one side band in the system of Fig. 1 would not be as complete as desired.

In order to improve the performance of the phase shifter 2 an additional resistor of substantial value is connected in series with the secondary winding of the transformer l9. This resistor may .have a value suflicient to maintain the current flowing through the secondary winding of the transformer l9 reasonably constant throughout the operating range of the phase shifter.

In addition, a parallel circuit containing an in- I effect of this parallel resonant circuit is to cause the curves representing the voltage between concluctors 23 and 25 and the voltage between the conductors 21 and 25 to approach each other more a closely over the desired range. For example they may intersect at four points over the frequency range applied to the phase shifter 2|. The deviation between the two curves at any point is small enough to assure excellent operation of the system. Moreover, the phase displacement between the two components is maintainedsubstantially uniform. In a phase shifter similar to the phase shifter 2|, tests have shown that it is possible with a range of input frequency of 250 to 4000 cycles per second to maintain the voltage outputs of the phase shifter balanced in amplitude within 4%, and constant in phase displacement within one degree of over the entire range.

The value of the resistor 85 may vary over a substantial range or the resistor may be omitted completely. Preferably, the value of the resistor 33 is selected to maintain the phase angle between the two output phase components of the phase shifter approximately 90 over a wide range of frequency; To this end, if the phase shifter is designedfor a 90 phase angle, the resistor 85 should have a value selected to make the phase angle substantially 90 at the limits of the frequency range to be handled by the phase shifter.

As examples of suitable values for the componentsof the phase shifter II, the following table is presented:

The coils may have a Q of 18 measured at a frequency of 1000 cycles per second.

The modulators II and I3 may be of any suitable type. However, it is desirable that balanced modulators be employed in order to suppress the carriers supplied thereto from the phase shifter 3. Although electronic tube modulators may be employed, barrier-layer modulators offer a number of advantages. Not only do they eliminate power sources, such as heater transformers and plate voltage supply sources, but they have extremely good modulation characteristics for single side-band work. In addition, the balance thereof may be adjusted by application thereto of direct current as hereinafter pointed out.

The most common barrier-layer rectifiers in use today are those known as selenium and copper-oxide rectifiers. have been particularly satisfactory for the modulators II and I3. They may be arranged in various ways as well known in the art. However, in Fig. 1, each modulator is of the ring type and employs four copper-oxide rectifiers 9|, 92, 93 and 95. As clearly shown on the drawing, each successive pair of copper-oxide rectifiers has a terminal disposed therebetween for connection to associated transformers. It will be noted that the four copper-oxide rectifiers are arranged substantially in a bridge. If each bridge is balanced, no carrier should appear in the output transformers 3| and 35. However, if a bridge is unbalanced, as by reason of inherent variations in the copper oxide rectifiers, some carrier may appear.

In order to balance or unbalance the modulators as desired, direct current is supplied thereto from a source represented by conductors L3 and L4. These conductors have two potentiometers 91 and 99 connected thereacross. The potentiometers respectively have adjustable taps I and I03 associated therewith. The tap IOI is connected through a resistor I08 and the conductor 23 to a center-tap 90 on the secondary winding 93 of the transformer 9. Similarly, the tap I03 is connected through a' resistor I and the conductor 21 to a center-tap won the secondary winding [3. In addition, a resistor I0'I having a grounded center-tap is connected between the conductors L3- and L4. Center-taps on the primary windings'of I of current therethrough, thIs tends to unbalance the bridge represented by the modulator I I, and

Copper-oxide rectifiers I 9 from the phase shifter 3.

the transformers 3| and 33 are connected to ground.

A rectifier of'the copper-oxide type has a resistance which varies inversely with the current flowing therethrough. Let it be assumed that the tap I03 is adjusted to make the center tap IC positive with respect to the center-tap 3IC.

0 Under these circumstances, current flows through the copper-oxide rectifiers 33 and 93. Since the resistance of such rectifiers varies as a function the extent of unbalance depends on magnitude of the voltage applied between the terminals IC and 3IC. The value of the voltage. in turn, is dependent on the adjustment of the tap I03;

Let it be assumed next that the tap I03 is adjusted to make the tap 'IC negative with respect to the tap 3IC. Under such circumstances, direct current will flow through the copper-oxide rectiflers 93 and 3|. This tends to unbalance the bridge, represented by the modulator I I in the opposite direction, and the extent of unbalance is adjusted by adjustment of the tap I03.

From the foregoing discussion, it will be clearly apparent that if no audio signal is supplied to the modulator I I, the carrier output of the modulator may be substantially suppressed by proper manipulation of the tap I03. In a similar manner, the tap |0| may be manipulated to adjust the modulator I 3.

Incertain cases, it may be desirable to unbalance deliberately one of the modulators. For example. in relaying work, operation of a relay may be employed for placing a carrier signal on the conductors LI, L2. Such a carrier signal may be produced by deliberately unbalancing one of the modulators II or I3. For example, operaexample, the voltage drops across the resistors 29 and 33 may be connected either additively or subtractively, depending upon the specific sideband desired. The side-band employed also may be changed by interchanging the connections of one of the transformers 3| or 35. or by interchanging the conductors 23 and 21, or by interchanging the inputs to the transformers I and If desired, the transformers 3| and 35 may be combined, thereby, providing a single secondary winding for connection to the amplifier 31. In this case, the inputs to the two modulators may be adjusted for balancing purposes. However,

the preferred embodiment is that illustrated in Fig. 1.

If it is desired to employ the upper and lower side-bands for separate purposes, connections similar to those illustrated in Fig. 2 may be employed. Referring to Fig. 2, it will be observed that two transformers 3IA and 35A are shown. These transformers correspond, respectively, to

I the transformers 3| and 35 of Fig. 1, and the primary connections thereof may be exactly the same as those illustrated for the transformers 3| and 33. It will be observed. however, that the transformer 3| has two secondary windings I|3 and H1. The transformer 35a also has two secondary windings H9 and I2I. By tracing the connections it will be observed that the windings H5 and H9 are connected in series opposition across the input of an amplifier I23. The same windings are connected in aiding series relationship across the input of an amplifier I25. In a somewhat similar manner, the windings III and I2I are connected in series opposition across the input to the amplifier I23, and in series aiding relation across the input to a consideration of Fig. 2, it will be clear that each of the amplifiers I23 and I25 supplies a separate one of the side-bands produced by the system of Fig. 1, I

For amplifying purposes, any suitable amplifier may be employed. As shown in Fig. 1, the amplifier 31 includes two pentode tubes I21 and I29 having plate electrodes I21a and I290, respectively, connected through a suitable plate resistor I29b and an inductance coil I2'Ib to a common conductor I3I. This conductor I3I is connected to the positive terminal of a source of direct voltage. The negative terminal of the source is connected to ground. The screen grids I210 and I290 of the pentodes also are connected to the conductor I3I. The suppressor grid I21d and cathode I21e of the pentode I21 are connected through a cathode resistor I21f and a bypass capacitor I21g to ground. In an analogous manner, the suppressor grid I29d and the cathode I296 of the pentode I29 are connected to ground through a cathode resistor I29 and a bypass capacitor I299.

The input to the amplifier the conductor 41 which is connected to trol grid I29h of the pentode I29. the pentode I29 is coupled through a coupling capacitor I33 to the control grid I21h, and a grid resistor I219 associated with the pentode I21. The output of the pentode I21 is applied through a coupling capacitor I35 to a parallel tuned circuit comprising an inductance coil I31 and a capacitor I39. This parallel tuned circuit is tuned substantially to the output frequency of the amplifier. The voltage across this circuit is coupled through the capacitors M and 5I to the conductors LI and L2. As shown in Fig. l, a center tap on the coil I31 is connected to ground.

It is'believed that the operation of the system is clear from the foregoing discussion. If it is desired to communicate by voice signal between the stations A and B, the voice signal is converted into a corresponding audio signal by means of the microphone I5. This audio signal is passed through the phase shifter 2| to provide two components differing in phase by approximately 90. Similarly the output of an oscillator I is passed through the phase shifter 5 to provide two components also differing in phase by substantially 90. These components are'supplied to the ring modulators i I and I3 to produce carrier-suppressed, double side-band outputs in the secondary windings of the transformers 3| and 35. The outputs of the transformers 3I and 35 are supplied to load resistors 29 and 33 and are combined to eliminate one of the side-bands. The resulting single side-band signal is amplified in the amplifier 31 and applied to the conductors LI and L2 through the coupling capacitors 49 and 5I. This single side-band signal is received by means of a suitable receiver 53 at station B. Similar equipment may be located at each station, if desired, to permit transmission of voice 31 is derived through the conthe amplifier I25. By I The output of communication from the station B to the station A.

If it is desired to transmit a carrier signal between the stations A and B, the contacts II3 are actuated to unbalance the modulator II. This results in the generation of a carrier signal which is amplified in the amplifier 31 and app e across the conductors LI and L2 for reception at the station B.

Sometimes it is desirable to employ a standard superheterodyne receiver for reception of Single side-band signals. A receiver of this type is 11- lustrated in block form in Fig. 3.

Referring to Fig. 3, it will be noted that the incoming single side-band signal is represented by the sum or difference of two frequencies fc and is which are, respectively, the carrier and signal frequencies. Either the sum or difference of these frequencies will be received depending on whether the upper or the lower side-band is to be employed. The incoming signal is mixed in a suitable mixer I4I with a frequency equal to fc+fi, wherein I1 is the intermediate frequency of the superheterodyne receiver. Consequently. the output of the mixer includes a frequency Jl-fs or f1+fs, depending on the specific sideband being received. This intermediate frequency is amplified in an intermediate frequency amplifier I43 and supplied to a suitable modulator I45 which may be in effect a second mixer stage. If automatic volume control is provided, the controlling signal for the automatic volume control should be derived from the intermediate frequency amplifier prior to demodulation. In the demodulator I45, the intermediate frequency signal is mixed with an oscillation having a frequency fl. Consequently, the desired signal fs is obtained from the demodulator I45 and may be employed to actuate any suitable translating device I41 such as a loudspeaker.

It will be noted that two specific frequencies .fc-l-fi and ii are injected, respectively, into the mixer MI and the demodulator I45. If separate sources are provided for these two oscillations, extreme stability would be required for both sources. I

In order to simplify the stability problems of the receiver, a local oscillator I49 is provided which is capable of generating a frequency fc. This local oscillator is designed to operate with great stability. Since an oscillator similar to the oscillator I of Fig. 1 normally will be available at each station for transmitting purposes, a portion of the output of the oscillator I may be employed in place of the local oscillator I49.

The output of the local oscillator I49 is supplied to a'mixer ISI. This mixer also receives an output from an oscillator I53 which generates an oscillation having substantially the frequency ,fi.

Consequently, the output of the mixer I5I provides the frequency ,fc-l-fl which is required for the mixer I4I. In addition, the oscillator I53 provides an oscillation of the frequency f1 required for the demodulator I45.

In the system of Fig. 3, the oscillator I53 need not be as stable as the oscillator I49. It will be recalled that the intermediate frequency amplifier I43 supplies to the demodulator a, quantity represented by the frequency fiat s. In the demodulator I45, a quantity is produced which is represented by the expression (fizfs) f1=: :f Consequently, if the frequency .fi varies, such variation does not affect the quantity represented by the frequency 2: which is supplied to the translating device m. Preferably the oscillator I53 should have a stability sufilcient to maintain the signal 112:!- within the pass band of the intermediate frequency amplifier I43. Consequently, the receiver of Fig. 8 requires great stability only in the local oscillator us. 1

Although the invention has been described with reference to certain specific embodiments thereof, numerous modifications are possible. Therefore. the invention is broadly set forth in the appended clalms.

I claim as my invention: 1. In a system for producing a single sideband quantity, means for producing a first carrier alternating quantity and a second carrier alternating quantity having a. substantial phase displacement therebetween. said first and second carrier quantities being of the same frequency, means for producing a first modulating quantity and a second modulating quantity having substantially said phase displacement therebetween, means for modulating said first carrier quantity by said modulating quantity to produce a first double sideband output, means for modulating said second carrier quantity by said second modulating quantity to produce a second double sideband output, said modulating means com-- prising barrier-layer modulator means, and means for combining said outputs to eliminate one of said sidebands.

2. In a system for producing a single sideband" quantity, means for producing a first carrier alternating quantity and a second carrier alternating quantity having a substantialphase displacement thel'ebetween. said first and second carrier quantities being of the same frequency, means for producing a first modulating quantity and a second modulating quantity having substantially said phase-displacement therebetween. means for modulating said first carrier quantity by said first modulating quantity to producesa first double sideband output, means for modulating said second carrier quantity by said sec: ondmodulating quantity to produce a second double sideband output, said modulating means comprising balanced barrier-layer modulator means wherein the carrier quantities are substantially suppressed, and means for combining said outputs to eliminateone of said sidebands.

3. In a system for producing a single sideband quantity, means for producing a first carrier alternating quantity and a second carrier alternating quantity having a substantial phase displacement therebetween, said first and second carrier quantities being "of the same frequency, means for producing a first modulating quantity and a second modulating quantity having substantially said phase displacement therebetween, means for modulating said first carrier quantity by said first modulating quantity to produce a first double sideband output, means for modulating said second carrier quantity by said second modulating quantity to produce a second double sideband output. said modulating means comprising balanced barrier-layer modulator means, means for adjusting the modulator means to eliminate substantially the carrier quantities, and means for combining said outputs to eliminate one of said sidebands.

4. In a system for producing a single sideband quantity, means for producing a first carrier alternating quantity and a second carrier alternating quantity having a substantial phase dis placement therebetween. said first and second carrier quantities being of the same frequency, means forproducing a first modulating quantity and a second modulating quantity having substantially said phase displacement therebetween, means for modulating said first carrier'quantity by said first modulating quantity to produce a first double sldeband output, means for modulating said second carrier quantity by said second modulating quantity to produce a second double sideband. output, said modulating means comprising balanced barrier-layer modulator means, means for adjusting the modulator means to eliminate substantially the carrier quantities, said last-named means comprising means for introducing direct current into the barrier-layer modulator means, and means for combining said outputs to eliminate one of said sidebands.

5. In an electrical system, a plurality of barrierlayer rectifiers, means connecting said barrierlayer rectifiers in. a circuit having parallel paths, and means for adjusting the relative impedances of said paths, said last-named means comprising means for passing biasing current through part of the barrier-layer rectifiers.

- a plurality of barrier-layer rectifiers, means connecting said barrier-layer rectifiers in a circuit having parallel paths each containing one of the barrier-layer rectifiers, and means for adjusting the relative impedances of said paths, said lastnamed means comprising means forpassing direct current through a preselected part of the barrierlayer rectifiers. v

'7. In a system for producing a modulated quantity, a barrier-layer modulator having a plurality of paths each containing a barrier-layer rectifier, and means for'passing direct current through at least part of said paths for modifying the impedance characteristics thereof.

8. In a system for producing a modulated quantity, a bridge modulator having four paths related to form abridge circuit, each of said paths including a barrier-layer rectifier, and meansuor passing direct current through certain of the paths for modifyingthe balance of the bridge circuit. i

9. In a system for producing a modulated quantity, a barrier-layer modulator having a plurallty of paths each containing a barrier-layer source, and means rerectifier, a direct voltage sponsive to the polarity of the source for selecdirect current through either of tivel directing 4 a pair of said barrier-layer rectifiers. 10. In a system for producing a modulated quantity, a ring modulator comprising four ringconnected copper-oxide rectifiers, minal intermediate each adjacent pair of rectihere to form a resultant bridge circuit. and m ns for applying a direct voltage between a first pair on of the terminals which are disposed on a diagonal of the bridge circuit and the remaining terminals for modifying the balance of the bridge'circuit, said means including means for adjusting the magnitude and reversing the polarity of the direct es voltage.

11. In a system for producing a single sideband quantity, means for producing a first quantity representing the sum of the bands of amodulated carrier, means for producing a second quantity representing the difference between said upper and lower sidebands, and means for combining said first and second quantities to eliminate one of the sidebands. said last-named means comprising an adjustable potentiometer energized by one of the quantities for adjusting 6. In an alternating-current electrical system,-

having a terupper and lower sideamaeso the relative amplitudes of the first and second quantities to effect substantially complete elimination of one of the sidebands. i

' 12. In a system for producing a single sideband quantity, means for producing a first carrier alternating quantity and a second carrier alternating quantity having a substantial phase dis- ..Dlacement therebetween, said first and second provide an adjustable output, means for modulating said'second carrier quantity by said second modulating quantity to produce a second double sideband output, said modulating means comprising balanced barrier-layer modulator means for adjusting the modulator means to eliminate substantially the carrier quantities, said last-named means comprising means for introducing direct current into the barrier-layer modulator means, and means for combining the adjustable output and the second double sideband output, whereby the outputs may be adjusted relative to each other to eliminate substantially one of the sidebands.

13. In a system for shifting the phase of an alternating quantity, means responsive to an alternating input for producing a first quantity and a second quantity having a substantial phase displacement therebetween, said first quantity varying as a function of frequency of the alternating input, means for producing a third quantity varying with the frequency of the alternating input in a manner substantially opposite to the variation of the first quantity, whereby the first and third quantities may be combined to produce a fourth quantity which is substantially less immune to variation in frequency of the alternating input than said first and third quantities, means associated with said first and second-named means for producing output circuits for said second and fourth quantities, and means for balancing the internal impedances of the output circuits to which the second and fourth quantities are applied.

14. In a system for shifting the phase of an alternating quantity over a substantial frequency range, means responsive to an alternating input for producing a first quantity and a second quan'-- tity having a substantial phase displacement therebetween, said first quantity varying as a function of frequency of the alternating input, means for producing a. third quantity varying with the frequency of the alternating input in a manner substantially opposite to the variation of the first quantity, whereby'the first and third quantities may be combined to produce a fourth quantity which is substantially less immune to variation in frequency of the alternating input than said first and third quantities, means associated with said first and second-named means for producing output circuits for said second and fourth quantities, and means for modifying the phase displacement of the second and fourth quantities adjacent the limits of the frequency range for which the phase shifter is designed.

15. In a system for shifting the phase of an alternating quantity, means responsive to an alternating input for producing a first quantity and a second quantity having a substantial phase displacement therebetween, said first quantity varying asv a function of frequency of the alternating input, means for producing a third quantity varying with the frequency of the alternating input in a manner substantially opposite to the variation of the first quantity whereby the first and third quantities may be combined to produce a fourth quantity which is substantially less immune to variation in frequency of the alternating input, means associated with said first and second-named means for providing output circuits for said second and fourth quantities, said second and fourth quantities having amplitudes which when plotted as a function of frequency have two points of intersection, and means for varying the amplitude of the second quantity relative to the amplitude of the fourth quantity.

as a function of frequency to provide more than two points of intersectionthereof, whereby the difference in the amplitudes of the second and fourth quantities is small over a substantial range of frequency variation of the alternating input.

16. A system as defined in claim 15 wherein the last-named means comprises a resonant circuit tuned to a frequency within the range of the alternating input, said resonant circuit being connected to alter the amplitude relationships of the second and fourth quantities as a function of frequency.

17. In a system for shifting the phase of an alternating quantity over the range of frequency required for intelligible speech, a circuit comprising a capacitor, a resistor and an inductance winding connected in series for energization from. a suitable source in accordance with the alterwith the voltage across said resistor, said capacitor and the inductance introduced by the first named inductance winding being resonated subternating quantity over the range of frequency required for intelligible speech, a circuit comprising a capacitor, a resistor and an inductance winding connected in series for energization from a suitable source in accordance with the alternating quantity, a first output circuit including an inductance winding connected for energization in accordance with the voltage across said capacitor, said inductance windings being mutually coupled to'induce in the second-named inductance winding a voltage which adds to the voltage across the capacitor to provide a resultant voltage which is substantially constant over a substantial range of variation in the frequency of the alternating quantity, and a second output circuit connected for energization in accordance with the voltage across said resistor, said output circuits having 15 r ing connected in series for energization from a suitable source in accordance with the alternating quantity, a first output circuit including an inductance winding connected for energization in accordance with the voltage across said capacitor,

said inductance windings being mutually coupled to induce in the second-named inductance winding a voltage which adds to the voltage across the capacitor to provide a resultant voltage which is substantially constant over a substantial range of variation in the frequency of the alternating quantity, and a second output circuit connected for energization in accordance with the voltage across said resistor, the series circuit connected for penergization from the suitable source including sufllcient resistance to maintain current supplied thereto from the source substantially independent of frequency throughout the operating range of the phase shifting system.

20. In a system for shifting the phase of an alternating quantity over the range of frequency required for intelligible speech, a circuit comprising a capacitor. a resistor and an inductance winding connected in series for energization from a suitable source in accordance with the alternating quantity, a first output, circuit including an inductance winding connected for'energization in j accordance with the voltage across said capacitor; said inductance windings being mutually coupled to induce in the second-named inductance winding a voltage which adds to the voltage across the capacitor to provide a resultant voltage which is substantially constant over a substantial range of variation in the frequency of the alternating quantity, and a second output circuit connected for energization in accordance with the voltage across said resistor, and a parallel resonant cir-' the resonant frequency of the parallel resonant circuit.

22., In a system for producing a single sideband quantity, means for producing polyphase carrier components comprising a first carrier phase component and a second carrier phase component, means for producing poiyphase signal components comprising a flrstsignal phase component and a second signal phase component, the phase displacements between the components being of appreciable magnitude and substantially equal for i the carrier and signal, a first barrier-layer ring modulator, a second barrier-layer ring modulator.

cult connected for energization from said suitable source.

21. A system as claimed in claim 20 wherein the parallel resonant circuit is tuned to resonate substantially at the geometrical mean of the'frequency range for which the system is designed.

and wherein the output circuits have substantially equal internal impedances, said capacitor and the inductance introduced by the first-named induct-,

ance winding being resonated substantially to with one of said components to the associated one of the modulators a direct-current quantity for modifyin the balance of the last-named modulator. 4

24. A system as defined in claim 23 wherein the balance-.control-means is adiustable for varying the magnitude and polarity of the direct-current quantity.

} BERNARD E. IENEHAN.

REFERENCES CITED The following references are, of record in the file of this patent:

UNITED STATES PATENTS 4 Number Name Date 1,666,206 Hartley Apr. 17, 1928 2,163,680 .Hansell June 2'7, 1939 2,173,145 winner Sept. 19, 1939 2,191,315 Guanella Feb. 20, 1940 2,400,133 Pray May 14, 1946 M iddel Jan. 14, 1947

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