US2423866A - Wave separator - Google Patents

Description

July 15, 1947. J. R. WOODYARD WAVE SEPARATOR 2 Sheets-Sheet 1 Filed May 3, 1944 INVENTOR day/v A. WOODY/MD j ATI'ORNEY .lulyal5, 1947.

J. R. WOODYARD WAVE SEPARATOR Filed May :5, 1944 2 Sheets-Sheet 2 D k m mm. w W O MR N M a lllll v\\ Patented July 15, 1947 WAVE SEPARATOR John Robert Woodyard, Garden City, N. Y., as-

signor to Sperry Gyroscope Company, Inc., a

corporation of New York Application May 3, 1944, Serial No. 533,992

11 Claims.

My invention relates to the art of Wave separators, generally, and more particularly refers to methods and apparatus for separating an amplitude modulated wave into its carrier and sideband components.

One of the principal objects of my invention is to provide a method and apparatus for separating an amplitude modulated wave into its carrier and side-band components without the use of sharply-tuned filter circuits.

Another object of my invention is to provide an electric circuit in which a modulated Wave may be diverted into a linear and non-linear channel and in which this divided voltage is subsequently combined in series opposition to suppress the carrier component of the modulated wave input.

It is a. further object of my invention to provide a wave separating circuit which will be free from the effects of fading.

A still further object of my invention is to arrange a circuit capable of separating a modulated wave into its carrier and side-band components with minimum power losses.

Other objects and advantages of my invention will become apparent as the description proceeds.

In a preferred form of my invention I provide a circuit having two parallel channels, each branch of which receives the modulated wave that is to be separated. In one channel of the circuit the modulated wave is passed through a voltage limiter, or non-linear element, and in the other it is passed through an amplifier, or linear element. Both of these elements are adjusted in a manner such that the point of intersection of their respective amplitude-gain curves corresponds to the average or carrier value of the input, and the outputs of the two channels are combined in series opposition to suppress the carrier component of the modulated wave input. This gives a circuit output which corresponds to the two side-bands of the modulated wave and the nonlinear channel may be tapped to furnish a voltage corresponding to the carrier component of the wave. A balanced modulator is interconnected between the two channels to eliminate the effects of fading and other slowly-varying random fluctuations.

A more comprehensive understanding of my invention Will be afforded by the following detailed description when considered with the accompanying drawings, in which Fig. 1 is a schematic circuit diagram of an embodiment of my invention;

2 Fig. 2 is a block diagram of a modified form thereof;

Fig. 3 is an amplitude-gain curve for a voltage limiting element employed in the circuits illustrated in Figs. 1 and 2; and

Fig. 4 is an amplitude-gain curve for a linear amplifier similarly employed.

Like reference numerals have been used throughout in the drawings to designate like parts.

In the form of my invention illustrated in Fig. 1, I have arranged a circuit provided with a pair of input terminals ll upon which an amplitude modulated Wave that is to be separated into its carrier and side-band components is received. From this point of the circuit the modulated Wave is transmitted into two parallel paths l2 and :3. Within the former channel the modulated wave is limited by a voltage limiter l4 and subsequently amplified in an amplifier Hi, both of which operate together as a non-linear amplifier, to deliver a voltage corresponding to the carrier component of the modulated wave impressed upon the input terminals H,

The modulated Wave is transmitted by means of a coupling transformer iii to the grid of an electronic discharge device I! which forms one of the component parts of Voltage limiter I4. Connected in the plate circuit of device ll are a plurality of unilateral current conducting elements l8 and i9 which may take the form of diodes, and which serve as voltage limiting elements of the circuit. The output of voltage limiter M is transmitted to the grid of an electronic discharge element 2| through the facilities of a coupling transformer 22. The coupling windings of this transformer are tapped to deliver the output of Voltage limiter M to an AVC branch of the circuit, later to be described.

Electronic discharge device 2| which forms the initial stage of amplifier 15, illustrated as a single stage amplifier, delivers its output in the coupling transformer 23 from which point it is taken to the output terminals 24, as a voltage corresponding to the carrier component of the modulated wave input. This voltage is also taken at the circuit points 25 for the purpose of combining it in series opposition with the output of channel M which comprises an amplifier 26 and a phaseshifting network 21. Amplifier 25, which, for the sake of convenience, is illustrated as having a single stage only, comprises an electronic dis charge device 28. This element receives on the grid electrode thereof the modulated wave from the input terminals ll through the coupling transformer 29. The output of this amplifier is delivered through the coupling transformer 3| and the phase shifting network 2! to be combined in series opposition with the output of channel [2. This produces an output voltage for delivery to terminals 32 corresponding to the side-band components of the modulated input. This latter voltage is also delivered to the primary winding of transformer 33 whose secondary winding is connected as a component part of a balanced modulator 34 comprising electronic discharge elements 35 and 36 and their associated elements. This voltage is modulated with the output voltage of limiter M which is taken from the coupling winding of coupling transformer 22, and in this manner balanced modulator 34 delivers a voltage whose DC component acts as an AVC voltage for amplifier 15 which controls the gain thereof.

In the above described circuit the vacuum tubes ll, 2|, 28, 35 and 35 are shown as pentodes by way of illustration. They are understood to be connected in a conventiona1 manner, that is, suppressor-grid to cathode and screen-grid to a source of positive D. C. voltage, which connections are omitted for the sake of clearness.

In operation the voltage limiter I4 which has an amplitude-gain curve similar to that illustrated in Fig. 3, is adjusted with amplifier 26 in a manner such that the latter elements amplitude-gain curve intersects as illustrated in Fig. 4 'with the superposed amplitude-gain curve of limiter It at a point 3'! corresponding to the average, or carrier, value of the input modulated wave. Through the action of voltage limiter M, which clips the side-band components of the modulated wave, a voltage correspondin to the carrier component of the wave is produced. This voltage is combined with the output of the linear amplifier 23 whose phase is shifted in the phase-shifting network 2'! to produce a voltage at the output terminals 32 corresponding to the side-band components of the modulated wave. Each of the circuit elements I l, I5, 26 and 34 is tuned by the variable capacitors associated with the coupling transformers H5, 22, 23, 28, 3| and 32. Although this tuning is not required to be very sharp, it is desirable for the purpose of eliminating harmonics of the carrier fre quency.

To counteract the effects of fading or compensate for other random fluctuations, an automatic volume control circuit comprising the balanced modulator 34 is provided. This circuit, which receives the output voltage circuit corresponding to the side-band components of the modulated wave, passes a direct current voltage to amplifier 5 to control the gain thereof. When none of the carrier is present in the voltage at terminals 32, the side-band components which are in phase opposition cancel out and no D. C. voltage is passed to the amplifier IS. A. C. components of voltage are eliminated by bypass condenser 33. When a portion of the carrier is present, this voltage is multiplied by the carrier voltage taken from the coupling windings of transformer 22 and a D. C. voltage is applied to the grid-cathode circuit of amplifier I5. This biases the amplifier in the proper sense to remove the carrier from its output and, accordingly, the circuit is maintained in a stable condition to pass only the side-band components of the modulated waves at output terminals 32.

In the modified form of my invention illustrated in Fig. 2, the circuit arrangement is similar to that shown in Fig. 1 and the voltage limiter M, the amplifiers I5 and 26 and balanced modulator 34 are connected in a circuit of their component parts connected as illustrated in Fig. 1. The essential difference between the two circuits rests in the manner in which the automatic volume control voltage is applied to the amplifiers. Additional amplifiers 38 and 39 are connected in circuit as a matter of choice and may be omitted, or other amplifiers added, depending upon the operation of the circuit desired. Amplifier 38 is employed to provide amplification for the carrier wave, and amplifier 39 is interposed between the balanced modulator 34 and the coupling transformer 32 to amplify the sideband input thereto. Further, the output of balanced modulator 34, which in the embodiment of my invention, illustrated in Fig. l, feeds an automatic volume control voltage to amplifier I5 only, is here connected to deliver a similar voltage in opposite phase to amplifier 26.

The operation of this modification of my invention is, of course, the same with the excel)- tion of the control provided by balanced modulator 34. As long as channels l2 and I3 are perfectly balanced, no portion of the carrier is present in the side-band output, and the output voltage of the balanced modulator 36 is zero. If unbalance occurs in either channel, a D. C. voltage is produced in one sense or the other which combines with the voltage of battery 4| to produce an AVC voltage which increases the gain of amplifier l6 and decreases the gain of amplifier 25, or conversely, depending upon the state of unbalance. Through the action of this voltage balance is again restored. By using sufficient amplification before the balanced modulator, that is, amplifier 33, balance of the circuit may be maintained as close as is desired.

It will be apparent that this circuit provides a means whereby a broadcast transmitter may be operated with high efficiency by amplifying the carrier and side-band components of the modulated wave separately. It also provides a means for increasing the percentage of modulation.

As many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a wave separator first and second chan nels for receiving an amplitude modulated wave having carrier and side-band components, a nonlinear element and an amplifying means connected in said first channel, coupling means interposed between said non-linear element and said amplifying means, a linear amplifying element and a phase shifting network connected in said second channel, circuit means for connecting said first and second channels in series opposition, and means responsive to the output of said non-linear element and the combined output of said first and second channels for automatically controlling the gain of the amplifier in said first channel.

2. An electronic wave separator comprising a non-linear amplifier and a linear amplifier having substantially hyperbolic and straight; line amplitude-gain curves, respectively, conducting means for impressing an amplitude modulated wave having carrier and side-band components upon both of said amplifiers, means for adjusting the gain of each of said amplifiers so that the point of intersection of their respective amplitude-gain curves corresponds to the average value of the modulated wave, and means for connecting the output of each of said amplifiers in series opposition to suppress the carrier component of said modulated wave.

3. Apparatus according to claim 2 including an automatic volume control means for controlling the gain of said non-linear amplifier.

4. Apparatus according to claim 2 including an automatic volume control means for controlling the gain of both the linear and non-linear amplifiers.

5. A wave separator comprising a first and second channel for receiving an amplitude modulated wave having carrier and side-band components, a voltage limiting and amplifying means connected in said first channel for clipping the side-band components and amplifying the carrier component of said modulated Wave, a linear amplifier connected in said second channel, means for connecting the outputs of said first and second channels in series opposition to deliver an output voltage corresponding to the sideband components of said modulated wave, and means for taking the output of said first channel, only, to deliver a voltage corresponding to the carrier component of said wave.

6. Apparatus corresponding to claim 5 including a balanced modulator responsive to the output of said first channel and to the combined outputs of both channels for automatically controlling the gain of an amplifier of said first channel.

7. Apparatus according to claim 5 includin a balanced modulator responsive to the output of said first channel and to the combined outputs of both channels for automatically controlling the gain of each of the amplifiers connected in said first and second channels.

8. A method for separating an amplitude modulated wave into its carrier and side-band components comprising the steps of amplifying the same non-linearly to produce a voltage corresponding to the carrier component of said Wave, amplifying the modulated Wave linearly to produce a voltage corresponding to the full modulated wave, controlling both processes of amplification to adjust the common point of their amplitude-gain curves to a value equal to the average value of the envelope of the modulated wave, and combining the voltages produced by both processes of amplification in series opposition to balance out or suppress the carrier component of said modulated wave.

9. An electronic wave separator comprising a non-linear amplifier and a linear amplifier, conducting means for supplying an amplitude-modulated wave having carrier and side-band components to both of said amplifiers, phase-shifting means in the output of said linear amplifier, and means connecting the phase-shifted output of said linear amplifier in opposition to the output of said non-linear amplifier to thereby produce the side-band components of said carrier.

10. Apparatus as defined in claim 9 including a balanced modulator connected to said nonlinear amplifier and to said connecting means for delivering automatic volume control voltage to said non-linear amplifier.

11. Apparatus as defined in claim 9 including a balanced modulator connected to said amplifiers and to said connecting means for delivering automatic volume control voltage to said amplifiers.

JOHN ROBERT WOODYARD.

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

UNITED STATES PATENTS Number Name Date Re. 15,089 Englund Apr. 19, 1921 1,976,457 Ohl Oct. 9, 1934

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