US2287173A - Means of radio transmission and reception by means of unidirectional modulation - Google Patents

Description

MEANS oF RADIO TRANSMISSION AND'RECEPT'ION BY MEANS oF AUNI-DIRECTIQNAL. NoDuLATIoN r Filed June e, 1940 June23, 1942. J HARTZ 2,287,173

IN VEN TOR.

Patented June 23, 1942 MEANS OF RADIO TRANSMKSSION AND RE- CEPTION BY MEANS 0F UNIDIRECTIONAAL MODULATION Julius Hartz, New Orleans, La.

Application June 6, 1940, Serial No. 339,124

6 Clallls.Y (Cl. 25o-6) My invention concerns anew method of carrler Wave transmission and reception, either by radio or wire. Specifically, my invention consists of a transmission system in which the actual transmitting carrier or carriers can be said to be uni-directionally modulated, as opposed to the present systems of sinusoidal modulation of the carrier or carriers.

We may have uni-directional modulation by amplitude, frequency or phase. It is also possible to carry out single side-band transmission using uni-directional modulation. Other systems should be known as sinusoida amplitude, frequency. phase, single sideband, double or plural modulation. Transmissions by my system should be known as uni-directional amplitude, frequency, phase, single sideband, double or plural modulation. l

"Sinusoidar modulation can be defined as a system of transmission in which the actual carrier or carriers are modulated byl both halves of an essentially sinusoidal wave in such a manner that the modulating currents imposed upon any single train of carrier waves can be said to be alternately polarized with respect to a zero value of the modulating wave; or by one or both halves of a complex modulating wave which, when rectiied, still contains sinusoidal variations of different frequencies in a single half cycle of its modulating envelope which it is necessary to I' transmit.

Uni-directional modulation can be defined as a system of transmission in which the actual carrier or carriers are modulated by a rectified version of an essentially sinusoidal wave in such a manner that the modulating currents imposed upon any single train of carrier waves can be said to be polarized in only one direction with respect to a Zero value of the modulating wave; or by only one half of a wave which, 'when rectif-led, does not contain any sinusoidal variations of a different frequency in a single half cycle of its modulating envelope which it is necessary to transmit.

Uni-directional modulation was originated to avoid the distortion in a single train of the actual transmitting carrier waves which takes place when we sinusoidally modulate that single train of actual carrier Waves. If we amplitude modulate a single radio frequency with just one whole sinusoidal cycle of a modulating wave, the author contends that, in addition to the amplitude modulation, there will be a concomitant phase modulation. This phase modulation will occur in the following manner: During the first quarter cycle i quency) of the modulating wave We Will have an increasing amplitude and an advancing phase; during the second quarter cycle we will have a decreasing amplitude and a retarding phase; during the third quarter cycle we will have a decreasing amplitude and a further retarding of phase, and during the fourth quarter cycle we will have an increasing amplitude and an advancing phase. An examination will consequently disclose a lack of symmetry, and the author contends that because of this lack of- Symmetry, and the subsequent distortion of the wave in passing through long distances, a sinusoidally modulated carrier wave will suffer an asymmetrical distortion which is not true of a uni-directionally modulated wave. The positive half and the negative half of themodulating wave would, in this case, be identical but of opposite sign, When this modulating wave isused to sinusoidally modulate a single carrier frequency, however, the modulated waves representing the positive half of the modulation and the modulated waves representing the negative half of the modulation are not identical (but of opposite sign). When we uni-directionally modulate as herein described, each half of the modulated modulating frequency serves to modulate a different actual transmitting carrier and each carrier is modulated in the same'identical manner, hence such a modulation, when re-combined, is symmetrical, thereby avoiding the asymmetrical distortion of a sinusoidal modulation.

In order that the terms used may be correctly understood, I give the following definitions:

Signal or modulating signal- The actual voice, music, etc., which we wish to transmit.

Modulated frequency or modulating frequency.-I"he radio frequency carrier or carriers upon which the modulating signal is imposed and which are then used to modulate the actual carriers.

Actual carrier or modulated carmen-The actual carrier or carriers used to transmit the signal through the ether, and which are modulated by a rectified version of the modulating frequency.

Uni-directional modulation is preferably carried out by rst using the complex modulating signal (music, speech, etc.) to'mod'ulate two different radio waves (of the same or different fre- We then have resulting wave forms which can be said to be essentially sinusoidal, and, if representing an amplitude modulation, to consist of positive and negative halves which can be said to be equally timed with respect to the Zero axis. When we rectify a wave of this form, we then have a pulsating wave, or one which can be said to be uni-directional with respect to the Zero axis. So a rectiiied version of the first modulated frequency or frequencies is then used to uni-directionally modulate the nal transmitting carrier or carriers (the actual carriers).

Since almost every sinusoidal transmission system in existence may have its counterpart in uni-directional modulation, it becomes obvious that to describe all the means by which we can carry out a uni-directional modulation would entail a description of nearly every transmission system known. I will describe several methods by which a uni-directional modulation may be carried out and will illustrate two. This will make the principles plain to anyone versed in the art. It must not be inferred that all the methods discussed represent the preferred way of carrying out the system, but they are presented merely as possible methods to illustrate the principles involved.

One basic description, when correctly understood, can be said to define uni-directional modulation and the primary points to be observed in carrying it out: The rst requirement is that the modulating signal (if complex audio or the like) be used to modulate the modulating frequency or frequencies We then have a modulating frequency which has equally timed positive and negative halves when considered with respect to its Zero axis. (3) Only a rectified version of any single modulating frequency can be imposed upon any single actual carrier and any half Vcycle of the modulating frequency must be free of any sinusoidal variations of different frequencies in its modulating envelope which it is necessary to transmit. (4) It is preferably desired to derive from a complex modulating signal two different modulating frequencies, one representing each half of the complex modulating signal. (5) It is then preferably desired to impose a rectified version of each modulating frequency (if of the same frequency) upon two actual carriers or (6) if the modulating frequencies are different frequencies to successively impose rectified versions of first one and then the other upon either a single or double actual carrier in such a manner that the rst trains of frequencies represent the positive half of the modulating signal and the second trains of frequencies represent the negative half of the modulating signal. (7) It is preferably desired that the transmission be carried out in such a manner that both the negative and positive halves of the modulating signal are represented by modulating frequencies being imposed upon the actual carriers in such a manner that the actual carrier trains always increase in amplitude from zero to maximum and back with each half cycle of the modulating signal. It would not be imperative to do this, since both halves of the complex modulating signal might be imposed upon a single modulating frequency, and a rectified version of this single frequency imposed upon a single actual carrier. While this latter would be possible, it would not represent the preferred manner of carrying out a uni-directional modulation as the author conceives it.

Since the modulating frequency is a modulated wave, then in order to convey the intelligence contained therein, it is only absolutely necessary to transmit a rectified version of this wave. Both halves of the modulating frequency can be imposed upon a single carrier by using full-wave rectification. To transmit both halves so that they arrive at destination in sinusoidal wave form, however, it is necessary to use differential transmission.

Figure 1 is a schematic diagram of one application of my invention applied to a radio transmitter.

Figure 2 is a schematic diagram of a receiver suitable for receiving the transmission of Figure 1.

Figure 3 is a schematic diagram showing a second version of the transmitter.

Figure 4 is a schematic diagram of a receiver to receive the transmission of Figure 3.

In Figure 1 a pair of constant frequency generators 3 4 are connected respectively to the input circuits of a pair of push-pull modulator tubes 6 1, whose output connects to the primary of transformer 8. The C battery 5, connecting to the grids of modulators 6 1, is normally adjusted in such a manner that in the absence of a modulation signal at l, no appreciable plate current will flow, hence the radio frequency currents being generated in the constant frequency generators 3 4 will not reach the output transformer 8. When a modulating signal S enters the jack l and through the differential transformer 2, the positive half of the modulating signal will modulate currents generated by 4, which will pass through the tube 'I to the primary 8. The negative half of the modulating signal will modulate currents generated by 3, which will pass through the tube 6 to the primary 8. In the second part of the circuit, we again go through a similar process. Here the constant frequency generators lil-Il connect to the modulators I3 I4, whose outputs |5-l6, respectively, pass through the primary Il to the power amplifier I8, thence to the antenna and ground |9 20. In the second half of the circuit, the C battery l2 so biasses the grids of modulators [3 l4 that in the absence of a modulating frequency at secondary 9, no plate current will flow, hence the output of the constant frequency generators lil-ll will not be able to reach the output transformers |5 IB. When a modulating frequency reaches the secondary 9, the positive half of the cycle will cause tube i3 to pass modulated currents originating at generator l. The negative half of the cycle will cause tube i4 to pass modulated currents originating at generator Il. In Figure 1 the constant frequency generators 3 4 always generate frequencies lower than generators lil-l I.

. In the authors experiments 3 4 were in the neighborhood of 40 kc. and Ill-ll were in the neighborhood of 1,000 kc. These are merely cited by way of example, as any frequencies may be chosen.

In Figure 2 the input circuit 2| tunes to the output of modulator i3, and the input circuit 22 tunes to the output of modulator I4. The modulation is detected by the detectors 23-24, in whose output circuit is connected the differential transformer 25. Detector 23 originates the positive half of the modulating frequency and detector 24 originates the negative half of the modulating frequency. The whole primary 25 is inductively connected to intermediate amplifiers 2li-2l. Amplifier 26 is adjusted to receive frequencies generated by 3, plus or minus the modulating signal S, and amplifier 21 is adjusted to receive the frequencies generated by 4, plus or minus the modulating signal. After detection by detectors 28 29, we find that one-half of the modulating signal originates at detector 28 and the other half at detector 29. They are rephased by the transformer 30 and are obtainable from the secondary 3|.

Figure 3 represents a possible variation of the transmitter. 'I'he parts shown in Figure 1 and numbered l to 8 would remain the same. At the output 8, we would now connect the input 32. A constant frequency generator 33 connects to one of the grids of modulator 35. The modulating grid of modulator 35 is so biassed by C battery 34 that in the absence of modulating currents at 32 no appreciable plate current will flow and the frequency 33 will not reach the output transformer 36. When a modulating frequency reaches the secondary 32, it causes modulated currents of frequency 33 to pass to the transformer 36, thence to the amplifier S1 where it is transmitted.

Figure 4 represents a receiver to receive the transmission of Figure 3. The tuned circuit 38 tunes to the frequency generated at 33, plus or minus the modulating frequencies F1 and F2 plus or minus the modulating signal S. After detection in the detector 39, the balance of the circuit il to 46 is similar to that shown in Figure 2 and numbered 26 to 31.

It is possible to sinusoidally modulate a single carrier and then use a rectified version .of this carrier to modulate a single actual carrier. This can be pictured by simply imagining the transmission as taking place from only the upper half of the transmitter shown in Figure l, with the bias on tube 6 adjusted to the mid-point rather than cut-off.

What is claimed is:

1. The combination in a modulation system of a modulated modulating high frequency source Whose wave form provides a succession of equal time period half waves alternately polarized respecting a zero value; a pair of voscillation generators each coupled to a modulator, which modulators in the absence of signals are biassed closely to cut-off, means for applying to the modulators the said alternately polarized modulating currents which currents, due to the bias on the modulators, result in uni-directional modulation of each carrier, and means for transmitting and receiving the said alternately polarized uni-directional modulations.

2. In a combination means for generating two high frequency carrier waves, each generator coupled to a modulator, which modulators in the absence of signals are biassed closely to cut-off, means for applying to one of the said modulators modulated high frequency modulating currents so that, due to the bias on the modulators, only currents polarized in .one direction respecting a zero axis are effective in effecting modulation, and means for applying to the other said modulator modulated high frequency modulating currents so that, due to the bias on the modulator, only currents polarized in the opposite direction respecting azero axis to those applied to the rst modulator are effective in effecting modulation, and means for transmitting and receiving the modulated oscillations.

3. In a combination means for generating two high frequency carrier Waves, each generator being coupled to a modulator, which modulators, in the absence of signals, are biassed closely to cut-off, means for applying modulated high frequency modulating currents to the said highly biassed modulators so that only uni-directional high frequency modulating currents polarized in one direction respecting a zero value are effective in effecting modulation of one of the said modulators, and uni-directional high frequency modulating currents polarized in the opposite direction respecting a zero value are effective in effecting modulation of the other said modulator, and means for transmitting and receiving the modulated waves.

4. The combination of means for alternately producing two modulated high frequency modulating waves each having equally timed positive and negative portions, a pair of modulators biassed to near cut-off in the absence of signal, to whose input circuits two oscillators are respectively connected, means for successively applying the two modulated high frequency modulating waves to the said modulators in such a manner that the positive portions of one of the modulated high frequency modulating waves which are polarized in one direction respecting a zero value are effective in effecting modulation of one. modulator, and the positive portions of the other modulated high frequency modulating wave which are polarized in the opposite direction respecting a zero value are effective in effecting modulation of the other modulator, and means for transmitting and receiving the resulting modulations.

5. The combination in a modulation system of means for causing the alternate halves of a modulating signal, which alternate halves may contain sinusoidal variations, to alternately modulate two high frequency modulating waves, means for causing the alternate halves of the resulting modulated high frequency modulating waves to alternately and differentially modulate two separate transmitting carriers inllsuch amanner that alternate halves of the modulated high frequency modulating waves cause the transmitting carriers to vary from zero amplitude to some maximum amplitude and back to zero during the modulating period of each single half cycle of the modulated high frequency modulating wave, which transmitting carriers can then be said to be uni-directionally modulated, one with modulated modulating currents of one direction respecting a zero value, and the other With modulated modulating currents polarized in the opposite direction respecting a zero value, and means for receiving and rephasing said modulations.

6. The combination in a modulation system of two high frequency modulating sources, each coupled to a modulator, which modulators in the absence of signals are biassed closely to cut-off, means for applying first from one and then the other said high frequency modulating source a modulated modulating frequency whose wave form provides a succession of equal time period half waves alternately polarized respecting a zero value, which alternately polarized half Waves, due to the bias on the modulators, cause alternate operation of the said modulators, thus resulting in uni-directional modulation of each modulator, one with modulating currents polarized in one direction respecting a zero value and the other with modulating currents polarized in the opposite direction respecting a zero value, means for transmitting, and means for receiving and rephasing the said modulated carriers.

J ULIUS HARTZ.

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