US2461646A - Carrier-wave communication system - Google Patents

Description

Feb. l5, 1949; H, M. Ewls CARRIER-WAVE COMMUNICATION SYSTEM Filed oet. 8, y1941 /Il O O AMPLIFIER FIG. I

MODULATED 'OFREOUENC DETECTOR AUDIO- FREQUENCY AMPLIFIER Alsll INVENTOR, HAROLD M.LEw|s ATTORNEY.

Disuncel Feb. 15, 1949. H. M. LEWIS CARRIERLWAVE COMMUNICATION SYSTEM Filed oci. 8, 1941 2 Sheets-Sheet 2 '0 AUDIO- FREQUENCY 0- AMPLIFIER o- 37 S 4|? a -O l O- INTERMEDIATE- FRQUENCY E AM LIFIER 0- OSGILLATGI'L` MODULATOR lA f MHH y Time.

Patented Feb. 15, 1949 2,461,646 CARRIER-WAVE COMMUNICATION SYSTEM Harold M. Lewis, Allenhurst, N. J., assigner, by mesne assignments, to Hazeltne Research, Inc., Chicago, Ill., a corporation of Illinois Application October 8, 1941, Serial No. 414,050

(Cl. Z50-6) 19 Claims.

The present invention relates to carrier-wave communication systems and, particularly, to systems of this nature which employ mobile transmitter apparatus of relatively low power for communication over relatively short distances.

It is frequently desirable that communication over distances of a mile or so be effected by a carrier-wave communication system which utilizes a transmitter apparatus of relatively low power. An example of this nature occurs in military operations where it is essential that a forward military unit be able to transmit information to a rear position. Although the distances to be covered may be only of the order of a mile or less, it has heretofore been necessary that the transmitting apparatus carried by the forward unit be provided with some form of power supply, generally one or more storage batteries or dry batteries or perhaps a hand-driven generator, by which to energize the transmitting apparatus. The reduction of weight of any apparatus carried by the forward unit is of paramount importance not only from the standpoint of maintaining a high degree of mobility of the apparatus but alsoto minimize the number of persons required to transport it. Dry batteries have a limited life and replacements must be carried by the forward unit or a line of supply be maintained to that unit. This applies with even greater force to the use of storage batteries which require periodic and frequent recharging. This problem is particularly troublesome in connection with a conventional transmitting apparatus which places a relatively heavy drain on the power source from which it is energized. To maintain an uninterrupted line of supply to a forward unit engaged in combat is in many cases exceedingly diflicult and frequently impossible. Consequently, communication with such forward unitsmay be subject to frequent and undesired interruptions due to the supply problem itself where energization of the transmitting equipment is by batteries. Energization by hand- I driven generators has the important disadvantage that at least two men are required to transport and operate each generator unit.

It is an object of the present invention, therefore, to provide a new 'and improved carrier-wave communication system of the type described which avoids one or more of the disadvantages and limitations of the prior systems of this nature.

It is an additional object of the invention to provide a carrier-wave communication system having one or more transmitter units which require no local source of energizing power and which, therefore, may be compact, of light weight, and of inexpensive construction insuringr a high degree of mobility and reliability of operation.

Itis a further object of the invention to provide a vcarrier-wave communication system having a transmitter 'apparatus adapted to be effectively energized solely by radiant energy from other transmitting apparatus located at a remote point therefrom, yet one which is of simple and rugged construction.

In accordance with the invention, a carrierwave communication system comprises a, transmitting station including means for generating and directly radiating a modulated carrier Wave as well as carrier-wave radiating means remotely situated from the station and adapted to be energized solely by the aforementioned carrier wave and thereby to reradiate carrier-wave energy directly radiated thereto from the station. The system includes means for modulating the reradiated carrier wave with the desired signal to be transmitted, means for receiving the reradiated carrier wave and dependent upon the modulation of the radiated carrier Wave for deriving from the received carrier wave the desired modulationsignal components thereof, and means coupled to the last-mentioned meansfor utilizing the desired modulation-signal components.

In one form of the invention, a carrier-wave communication system of the type described comprises a transmitting station including means for generating and directly radiating a carrier Wave frequency-modulated with a periodic modulating signal of approximately saw-tooth wave form. The system includes an antenna means remotely situated from the station and tuned to the nominal frequency ofthe carrier wave to reradiate the carrier-wave energy directly radiated thereto from the station. The system also includes means for modifying the tuning of the antenna means to modulate the reradiated carrier wave with the desired signal to be transmitted.

In a particular form of the invention, the antenna means may comprise a loop antenna and the means for modifying the tuning of the antenna may comprise circuit-interrupting means included in circuit with a winding of the loop antenna.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

Referring now to the drawings, Fig. 1 represents a circuit diagram, partly schematic, of a complete carrier-Wave communication system embodying the present invention; Figs. 2 and 3 are graphs illustrating certain operating relations occurring in the arrangement of Fig, 1 and are used as an aid in explaining the operation of the invention; Fig. 4 is a circuit diagram, partly schematic, of a portion of a complete carrierwave communication system and represents `a modified form of the invention; Fig. 5 is a graph representing a certain operating `condition occurring in the arrangement `of Fig. 4 4and .is used as an aid in explaining the operation thereof; and Fig. 6 represents a modied form of the Fig. 4 arrangement. v

Referring now more particularly to Fig. l oi the drawings, there is represented schematically a complete carrier-wave communication system embodying the present invention in a preferred form. The system includes a transmitting station Ill including means for generating and directly radiating a carrier Wave frequencymodulated with a periodic modulating signal of approximately saw-tooth wave form. This means comprises an ampliner II having an output circuit coupled to a dipole antenna I2, I3 and having an input circuit coupled to the output circuit of a frequency-modulated oscillator I4. The oscillations generated by the oscillator I4 are frequency-modulated with a periodic modulating signal applied to the oscillator I4 from a modulation-signal generator I5. The latter generates a modulating signal of approximately symmetrical or linear saw-tooth wave form and may comprise, for example, a condenser rotated at constant speed by a motor IG which is energized from an alternating-current source I'I. Means is provided for amplitude-modulating the carrier wave generated by the frequency-modulated oscillator I 4 comprising a manually-operable key I8 which is coupled to a modulation circuit of amplier II in conventional manner.

The carrier-Wave communication system also includes carrier-wave radiating means remotely situated with respect to the transmitting station I9 and adapted to respond to a carrier wave radiated by the transmitting station and to reradiate carrier-wave energy directly radiated to the remotely-situated carrier-wave radiating mea-ns from the transmitting station I9. This means comprises a loop antenna I9 and means for tuning the antenna I9 to the nominal frequency of the carrier Wave radiated by the transmitting station I0 comprising a condenser 20 connected in circuit with the loop antenna. There is also included means for modifying the tuning of the antenna I9 to modulate the carrier wave reradiated thereby with the desired signal to be transmitted comprising circuit-interrupting means, here represented as a manually-operable key 2I, included in circuit with the winding of the loop antenna I9.

The system also includes means situated at a point remote from the antenna I9 for receiving the reradiated carrier wave and dependent upon the modulation of the radiated carrier Wave for deriving from the received carrier wave the desired modulation-signal components thereof. This means comprises a carrier Wave receiver 22 which is here shown as being positioned in the general locality of the transmitting station IIJ. The receiver 22 includes a detector 23 having an input circuit coupled to a dipole antenna 24, 25 and having an output circuit coupled to the input circuit of an audio-frequency amplifier 2S, which may include one or more stages of arnpliilcation, having an audio-frequency band-pass lter 21 included in the signal channel thereof.

The output circuit of the amplier 26 is coupledv to `a signal-reproducing device, for example, a pair of headphones 28 `for `utilizing the desired modulation-signal components.

Considering now the operation of the carrierwave communication system just described, and referring to the curves of Fig. 2, the carrier wave generated by the transmitting station I 0 and directly radiated from the antenna I2, I3 is frequency-modulated by the saw-tooth modulation signal generated by unit I5 and thus varies between a lower frequency fl and an upper frequency f2 as represented by curve A. This carrier wave travels to the antenna I9 and, assuming that the key 2l is operated to close its contacts, is 4reradiated by antenna I9. That is, the electromagnetic component of the radiated wave from the transmitting antenna I2, I3 cuts the loop antenna I9 and induces a current therein which sets up an opposing electromagnetic eld 180 .electrical degrees out of phase with the electrornagnetic field of the directly-radiated carrier wave at the loop antenna I9. This opposing electromagnetic field constitutes the reradiated carrier wave of the antenna I9. In this connection, it may be noted that the reradiated carrier Wave of antenna I9 is commonly referred to as a reflected carrier wave, but actually there is no essential difference since the latter merely is the observed result of the fact that an opposing electromagnetic field is set up in the antenna I9. Thus, the reradiated carrier wave of the antenna I9 is of the same character as a reflected carrier wave from any conductive object positioned in the path of the directly-radiated carrier wave. Since the strength of the opposing electro magnetic field set up by the antenna I9 varies with the current flowing therein, it will be seen that the tuning of the antenna I 9 to the nominal frequency of the directly-radiated carrier Wave results in the maximum now of carrier-wave current therein and thus the maximum opposing electromagnetic field being set up by the loop antenna I9, or, in other words, insures that the reradiated carrier wave shall have maximum intensity. The reradiated carrier wave thus has the same intensity as does the directly-radiated carrier wave at the loop antenna I9, except for the circuit losses of the latter due to its inherent resistance. The circuit losses, of course, are supplied by absorption from the directly-radiated carrier Wave. Hence, for maximum intensity of the radiated carrier wave, the resistance of the antenna I9 should be minimized. The reradiated carrier Wave is received by the dipole antenna 24, 25 `after a lapse of time t1 which is required for the directly-radiated carrier Wave to travel from the transmitting station I 0 over the distance r to the antenna I9 and for the reradiated carrier wave to travel from the antenna I9 over the same distance to the antenna 24, 25. The reradiated carrier wave received by the antenna 24, 25 thus varies in frequency as represented by curve B, and is applied to the input circuit of the detector 23. The antenna 24, 25 is relatively closer spaced to the transmitting antenna I2, I 3 and thus receives the directly-radiated carrier wave, represented by curve A, and applies this carrier wave also to the input circuit of the detector 23. There is thus applied to the input vcircuit of the detector 23 two carrier waves which distance r that the standing carrier wave will have a substantial intensity `at the receiving antenna 24, 25. From these applied carrier waves, the detector 23 derives in its output circuit a beat-frequency signal, represented by curve C, which has a constant value of frequency f3 during the time intervals tz, t2', etc., the constant frequency f3 of this signal being within the audiofrequency range and varying with the distance r of the loop antenna I9 from the transmitting station I9. This beat-frequency signal is applied to the audio-frequency amplifier 2li where it is amplied and applied to the telephones 28 for reproduction thereby.

Assume now that at a time t3 the key 2l is operated to open its contacts. The antenna I9 is now no longer responsive to the carrier wave radiated thereto from the transmitting station I0, since the loop winding of antenna I9 is now tuned by its inherent eapacitances to some frequency remote from that of the directly-radiated carrier wave, and hence does not reradiate any carrier wave. is developed in the output circuit of the detector 23 and no sound is produced in the telephones 28 until the key 2I is again cl-osed, as at the time t4 to render the antenna I9 again responsive to the carrier wave directly radiated thereto. It will thus be evident that the key 2| is effective to arnplitude-modulate the carrier wave reradiated by the antenna I9 with the desired signal to be transmitted, which signal, in the arrangement of Fig. 1, will be a coded signal of dotsand dashes of conventional form. In this connection, it will be understood that for purposes of simplifying the description of the operation of the invention, the keying time interval ts-t4 in Fig. 2 is not drawn to scale with respect -to the period ti-tz of the modulation signal generated by unit I and in practice the latter will be much shorter than any keying interval.

Accidental reflections of the carrier wave radiated by the transmitting station I0 may occur from surrounding objects, as houses and trees, and will be received by the antenna 24, 25 to produce in the output circuit of the detector 23 corresponding beat-frequency signals, but these will be of constant tone, vof different pitch, and of less amplitude than those produced by the desired signals. It will, therefore, be easy to distinguish the louder keyed signal from the spurious undesired signals produced by such accidental reflections of the directly-radiated carrier wave. However, further to guard against interference from such accidental reections, the amplifier 2-6 includes the audio-frequency band-pass filter 21 which may be sharply tuned to the constant frequency fa of the beat-frequency signal produced by reradiation from the antenna I9, thus rejecting all spurious beat-frequency signals which do not have a frequency approximately that of the desired signal.

The nominal frequency of the carrier wavel Consequently, no beat-frequency signal l in the output of the detector 23 it will be evidentv radiated by the transmitting station I0 preferably lies in the high-frequency portion of the frequency spectrum. This` not only reduces the physical size of the loop antenna I9 for optimum response to the radiated carrier wave, but additionally permits the use of directive radiators in place of the dipole antenna I2, I3 or in conjunction therewith, thereby to increase the intensity of the carrier wave at the antenna I9.

The antenna 24, 25 is preferably so arranged that it does not receive an undue excitation from the directly-radiated carrier wave. This may be accomplished by arranging the antennas I2, I3

and 24, 25 in physical proximity with the dipole elements radiating from the same central point and by arranging the antenna 24, 25 at right angles to the antenna I2, I3.

Instead of developing a lbeat-frequency signal that any conventional form of detector may be used for detector 23 by which directly to detect the amplitude-modulation components of only the carrier wave reradiated by the loop antenna I9. In this event, the antenna 24, 25 should be well shielded from the antenna I2, I3 and the directly-radiated carrier wave and the reradiated carrier Wave may have the same constant frequency, if desired.

It can be shown that the constant frequency f3 of ythe beat-frequency signal developed in the output circuit of the detector 23 from the directly-radiated and reradiated carrier Waves has a value determined from the following relation:

where:

Fa--the value of the constant frequency ,f3 of the developed beat-frequency signal,

Fdv=the range of frequency deviation of the directly-radiated carrier wave,

Tm=onehalf the period of the modulation signal generated by unit I5,

M=the number of cycles of Fd in the interval t2 ,A representative variation of the beat-frequency signal f3 with the distance r of the loop antenna I9 from the transmitting station I9 is represented by curve D of Fig. 3. It will be evident from this curve that the beat-frequency signal has a minimum useful value at a short distance r1 and a maximum useful Value at a longer distance r2, which limitations are placed upon the apparatus by the range of beat-frequency signals which are audible. The minimum useful range r1 may be decreased by decreasing the period Tm of the modulation signal generated by unit I5 or by increasing the range of frequency deviation Fav of the directly-radiated carrier wave. Corr-espondingly, the maximum useful range r2 o-f the system may be increased by increasing the period of the modulation signal or by decreasing the range of frequency deviation of the directlyradiated carrier wave.

The loop antenna I9 normally will have sufcient inherent resistance to be responsive to the directly-radiated carrier waves over the entire range 4of frequency deviation of the latter. If this is found not to be the case, a resistor of small value may be inserted in circuit with the loop antenna I9, thereby broadening its response. Any resistance in antenna- I9 decreases the intensity of the reradiated carrier wave, as previously1 :menus sible consistent with adequate response o! the antenna to the directly-radiated carrier wave over the range of frequency deviation of the latter. In practice, the inherent resistance of the loop antenna |9, even though kept at a minimum value, will generally be more than adequate for this purpose since the range of frequency deviation of the directly-radiated carrier wave will be small in comparison with the nominal frequency thereof, especially where the nominal frequency is quite high, for example, above 20 or 30 megacycles.'

From the above description of the Fig. 1 arrangement, it will be evident that the key 2| comprises means coupled to the carrier-wave reradiating means comprising the antenna |9 for eiectively modifying the response thereof to the directly-radiated carrier Wave to modulate the reradiated carrier wave with the desired signal to be transmitted. In other words, the key 2| effectively modiiies the tuning of the antenna I9 to the directly-radiated carrier wave, thereby to modulate the reradiated carrier wave with the desired signal to be transmitted.

Fig. Il represents schematically a portion of a carrier-wave communication system and shows a modified form of the carrier-wave radiating means which is remotely situated from the transmitting station. In this modified form of the invention, the carrier-wave radiating means comprises an antenna system shown as a dipole antenna 23, 3d. Since it may be desirable to mount the dipole antenna upon a mast, a, resonant transmission line 3| is coupled to the antenna to permit this to be done. The resonant transmission line, which may be either a real or artificial line in the form of an impedance network or a combination of the two, has an elective electrical length of one-half or multiples of one-half of the nominal wave length of the carrier wave radiated by the transmitting station. Circuit-interrupting means, comprising a manually-operable key 32, is coupled to the transmission line 3| selectively to short-circuit and open-circuit the remote end thereof and thereby modify the resonant characteristic of the line. This causes the antenna respectively to reradiate and not to reradiate the directly radiated carrier-Wave energy, thereby to modulate the reradiated carrier wave with a desired signal to be transmitted. This modified form of the invention also includes means coupled to the carrier-wave radiating means for deriving from the directly-radiated carrier Wave a desired modulation signal with which the latter carrier wave has been modulated, as by operation of the key I8 of the Fig. l arrangement. This means comprises a carrier-wave receiver 33 having an input circuit coupled through a transmission line 3d to a quarter wave length or potential antinode point of the transmission lineI 3|. The transmission line 36 is terminated by a resistor 35 to avoid reflections. The receiver 33 includes an oscillatormodulator 36 which is coupled to the transmission line 33 for converting a received carrier wave to an intermediate-frequency carrier wave. Coupled to the output circuit of the oscillator-modulator 36, in the order named, are an intermediate-frequency ampliiier 3l of one or more stages, a frequency detector 38, an audio-frequency ampliiier 39 of one or more stages, and a signal-reproducing device comprising a pair of headphones 4G. The detector 38 comprises an input transformer 4| having primary and secondary windings tuned to the nominal frequency of the carrier wave applied thereto from the intermediate-frefluency amplifier 31. The detector also includes a rectifier device 42 and load impedance 43 therefor, the load impedance being coupled to the input cir-cuit of the audio-frequency amplifier 39.

The operation of this modified form of the inve'ntion is essentially similar to that of the Fig. 1 arrangement insofar as the reradiation of a received carrier wave is concerned. That is, the antenna 29, 30 sets up an electromagnetic field opposing that of the directly-radiated carrier wave, thus reradiating or reiiecting the directlyradiated carrier wave. It is only necessary to add that the operation of the key 32 effectively modies the response of the antenna 29, 30 to the received 'carrier wave, whereby the reradiated carrier Wave is modulated with a desired signal to .be transmitted. In this regard, the transmission line 3| acts as an impedance having a value at its input end substantially equal to that at its remote end, thus having large impedance across its input terminals when the key 32 is open and substantially zero impedance when the key 32 is closed. In considering the operation of the receiver 33 of this modication, and referring to the curves of Fig. 5, the receiver 33 is coupled through the transmission line 34 to a potential antinode 0n the transmission line 3|, whereby a received carrier wave is applied to the input circuit of the oscillator-modulator 36. The oscillator-modulator 36 converts the received carrier Wave to an intermediate-frequency carrier wave which is amplified by the amplifier 31 and applied to the frequency detector 38. Since the received carrier wave is frequency modulated, as represented bythe curve A' of Fig. 5, and since the detector input transformer 4| is tuned to the nominal frequency of the carrier wave applied thereto, an audio-frequency signal is derived across the rectifier load impedance 43 having an amplitude characteristic as represented by curve E. This signal effectively constitutes a keying tone which appears when the key |8, Fig. 1, is closed, as during the interval ts, and is absent when the key is open, as during the interval te, whereby the desired signal is transmitted in code form as dots and dashes in conventional manner. rhe audio-frequency signal derived across the rectifier load impedance 43 is amplified by the audio-frequency amplier 39 and is reproduced by the signal-reproducing device 40.

It may be noted that when the modied form of the invention of Fig. 4 is used with a transmitting station of the type shown in Fig. 1, a twoway carrier-wave communication system is provided and the two-way operation is conventional in that the station which wishes to receive closes its key while the other transmits. Each station can break in as a side-tone signal is heard by the operator who is transmitting and this is interrupted when the key of the other station is opened.

It will be evident from the foregoing description of the invention that the carrier-wave communication system thereof comprises a transmitting station 0 which includes means for generating and directly radiating a modulated carrier wave having both amplitude-modulation and frequency-modulation components. One type of the modulation components comprises a signal to be transmitted to a remote point. There is also provided in the system means, including a dipole antenna 29, 30, situated at the remote point and adapted to respond to the carrier wave and to reradiate carrier-wave energy directly radiated thereto from the station I0. Means, comprising or closed.

the carrier-Wave receiver 33,is included in the last-mentioned means and is responsive to the aforementioned one type of modulation components for deriving and utilizing the transmitted signal. The means situated at the remote point also includes means comprising the key 32 for modulating the reradiated carrier Wave with a second signal to be transmitted. Receiving means in the system, this means comprising a radio receiver 22, receives the reradiated carrier wave and is dependent upon the other type of the modulation components of the radiated carrier wave for derivingfrom the received carrier wave the second signal. The derived signal last mentioned is applied to the head phones 28 for utilization.

Fig. 6 represents an additional form of carrier- Wave radiating means essentially the same as that of Fig. 4, similar circuit elements being designated by similar reference characters,l except that t'he transmission -line 3| in this instance has a length equal to one-fourth or odd multiples of one-fourth of the nominal wave length of the received carrier wave and the key 32 is arranged to open-circuit the remote end f the transmission line 3l to condition the antenna 29, 393, to reradiate the carrier wave received thereby. Here the transmission line 3i', as before, has a value of, impedance across its input terminals which depends upon whether the key 32 is open In this modication, however, the input terminal impedance is very large when the key 32 is closed and substantially zero When the key 32 is open. The operation of this modified form of carrier-Wave radiating means is otherwise essentially similar to that of Fig. 4 and will not be repeated.

While the inventionv has been described as embodied in a radio carrier-Wave system, it will be evident that the invention is equally suited for use in a system employing supersonic sound Waves.

From the above description of the invention it will be evident that a carrier-Wave communication system embodying the invention has the advantage that arelatively light weight, inexpensive, rugged and highly reliable transmitter unit is provided. This unit contains no vacuum-tube apparatus and thus is not subject to failures due thereto, nor does it possess any moving parts except a circuit interrupter by which the reradiated carrier Wave is modulated With the desired signal to be transmitted, nor does it require any source of battery power of any type for energization. The antenna of the transmitter unit thus provided may be made quite small Where carrier waves of high irequency are used for communication, thus enabling the transmitter unit to be easily transported by a single person. These advantages are -of great importance in many applications, as, for example, in military operations..

While there have been described what are at.

present considered to be the preferred embodiments of'this invention, it Will be obvious to those skilled in the art that various changes and modications may be made therein Without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A carrier-Wave communication system comprising, a transmitting station including means for generating and directly radiating a modulated carrier Wave, carrier-Wave radiating means remotely situated from said station and adapted to be solely energized by said carrier Wave and thereby to reradiate carrier-Wave energy directly radiated thereto from said station, means for modulating said reradiated carrier Wave with a desired signal to be transmitted, means for receiving said reradiated carrier Wave and dependent upon the modulation of said radiated carrier wave for deriving from said received carrier wave .the desired modulation-signal components thereof, and means coupled to said last-mentioned means for utilizing said desired modulationsignal components.

2. A carrier-Wave communication system comprising, a transmitting station including means for generating and directly radiating a frequencymodulated carrier wave, carrier-Wave radiating means remotely situated from said station and adapted to respond to said carrier wave and to reradiate carrier-Wave energy directly radiated thereto from said station, means coupled to said carrier-Wave reradiating means for modulating said reradiated carrier Wave with a desired signal to be transmitted, means for receiving said reradiated carrier Wave and dependent upon the frequency modulation of said radiated carrier Wave for deriving from said received carrier Wave the desired modulation-signal components thereof, and means coupled to said last-mentioned means for utilizing said desired modulationsignal components.

3. A carrier-Wave communication system comprising, a transmitting station including means for generating and directly radiating a carrier wave frequency-modulated with a periodic modulating signal, carrier-Wave radiating means remotely situated from said station and adapted to respond to said carrier wave and to reradiate carrier-Wave energy directly radiated thereto from said station, means for modulating said reform, carrier-Wave radiating means remotely situated from said station and adapted to respond to said carrier wave. and to reradiate carrier-Wave energy directly radiated thereto from said station, means for modulating said reradiated carrier Wave with a desired signal to be transmitted, means for receiving said reradiated carrier Wave and dependent upon the frequency modulation of said radiated carrier wave for deriving from said received carrier Wave the desired modulation-signal components thereof, and means coupled to said last-mentioned means 'for utilizing said desired modulation-signal components.

5. A carrier-wave communication system comprising, a transmitting station including means for generatingand directly radiating a carrier Wave frequency-modulated With a periodic modulating signal of approximately linear saw-tooth Wave form, carrier-Wave radiating means remotely situated from said station and adapted to respond to said carrier Wave and to reradiate carrier-Wave energy directly radiated thereto from said station, means for modifying the response of said carrier-Wave reradiating means to said di rectly-radiated carrier wave to modulate said reradiated carrier wave with a desired signal to ce transmitted, means for receiving said reradiated carrier wave and dependent upon the frequency modulation of said radiated carrier wave for deriving from said received carrier Wave the de sired modulation-signal components thereof, and means coupled to said last-mentioned means for utilizing said desired modulation-signal components.

6. A carrier-wave communication system comprising, a transmitting station including means for generating and directly radiating a carrier wave frequency-modulated with a modulation signal of approximately symmetrical saw-tooth Wave form, antenna means remotely situated from said station and adapted to respond to said carrier wave and to reradiate carrier-Wave energy directly radiated thereto from said station, means for modulating said reradiated carrier wave with a desired signal to be transmitted, means for receiving said reradiated carrier wave and depend ent upon the frequency modulation of said radi ated carrier Wave for deriving from said received carrier wave the desired modulation-signal ccmponents thereof, and means coupled to said lastmentioned means for utilizing said desired modulation-signal components.

7. A carrier-Wave communication system comprising, a transmitting station including means for generating and directly radiating a frequencymodulated carrier wave, antenna means remotely situated from said station and tuned to the nominal frequency of said carrier wave to reradiate carrier-wave energy directly radiated thereto from said station, means for modulating said reradiated carrier wave with a desired signal to be transf mitted, means for receiving said reradiated carrier Wave and dependent upon the frequency modulation of said radiated carrier Wave for deriving from said received carrier wave the desired modulation-signal components thereof, and means coupled to said last-mentioned means for utilizing said desired modulation-signal components.

8. A carrier-Wave communication system comprising, a transmitting station including means for generating and directly radiating a modulated carrier Wave, an antenna remotely situated from said station, means for tuning said antenna to be responsive to said carrier Wave and to reradiate carrier-Wave energy directly radiated thereto from said station, means for modifying the tuning of said antenna to modulate said reradiated carrier Wave with a desired signal to be transmitted, means for receiving said reradiated carrier wave and dependent upon the modulation of said radiated carrier wave for deriving from said received carrier wave the desired modulationesignal components thereof, and means coupled to said last-mentioned means for utilizing said desired modulation-signal components.

9. A carrier-Wave communication system comprising, a transmitting station including means for generating and directly radiating a modulated carrier Wave, antenna means remotely situated from said station and adapted to respond to said carrier wave and to reradiate carrier-wave energy directly radiated thereto from said station, circuit-interrupting means included in circuit with said antenna means for modulating said reradiated carrier wave with a desired signal to be transmitted, means for receiving said reradiated carrier waver and dependent upon the modulation of said radiated carrier wave for deriving from said received carrier Wave the desired modulation-signal components thereof, and means coupled to said last-mentioned means for utilizing said desired modulation-signal components.

10. A carrier-wave communication system comprising, a transmitting station including means for generating and directly radiating a modulated carrier Wave, a loop antenna remotely situated from said station and adapted to respond to said carrier Wave and to reradiate carrier-Wave energy directly radiated thereto from said station, circuit-interrupting means included in circuit with a winding of said loop antenna for modulating said reradiated carrier wave with a desired signal to be transmitted, means for receiving said reradiated carrier wave and dependent upon the modulation of said radiated carrier wave for deriving from said received carrier Wave the desired modulation-signal components thereof, and means coupled to said last-mentioned means for utilizing said desired modulation-signal components.

11. A. carrier-wave communication system comprising, a transmitting station including means for generating and directly radiating a carrier Wave, an antenna system remotely situated from said station, resonant means coupled to said antenna system to adapt said system to respond to said carrier Wave and to reradiate carrier'-.vave energy directly radiated thereto from said station, means for modifying the resonant characteristic of said resonant means to` modulate said reradiated carrier wave. with a desired signal to he transmitted, means for receiving said reradiated carrier wave and for deriving therefrom the desired modulation-signal components thereof, and means coupled to said last-mentioned means for utilizing said desired modulation-signal compc nents.

12. A carrier-wave communication system comprising, a transmitting station including means for generating and directly radiating a carrier wave, a dipole antenna, a resonant transmission line coupled to said antenna to adapt said antenna to be responsive to said carrier wave and to reradiate carrier-wave energy directly radiated thereto from said station, means coupled to said transmission line for modulating said reradiated carrier wave with a desired signal to he transmitted, means for receiving said reradiated carrier Wave and for deriving therefrom the desired modulation-signal components thereof, and means coupled to said last-,mentioned means for utilizing said desired modulation-signal components.

13. A carrier-Wave communication system comprising, a transmitting station including means for generating and directly radiating a carrier Wave, a dipole antenna, a resonant transmission line coupled to said antenna to adapt said antenna to be responsive to said carrier wave and to reradiate carrier-wave energy directly radiated V' thereto from said station, circuit-interrupting means coupled to said transmission line selectively to short-circuit and open-circuit the remote end thereof to modulate said reradiated carrier wave with a desired signal to be transmitted, means for receiving said reradiated carrier Wave and for deriving therefrom the desired modulation-signal components thereof, and means. Coupled to said last-mentioned means for utilizing said desired modulation-signal components.

14. A carrier-wave communication system comprising, a transmitting station including means for generating and directly radiating a carrier Wave, a dipole antenna, a resonant transmission line coupled to said antenna and having an eiective length equal to multiples of one-half the nominal wave length of said carrier Wave to adapt said antenna to be responsive to said carrier Wave and to reradiate carrier-Wave energy directly radiated thereto from said station, circuit-interrupting means coupled to said transmission line at the end thereof remote from said antenna selectively to short-circuit and open-circuit the said remote end to cause said antenna respectively to reradiate and not to reradiate said directly-radiated carrier-Wave energy, thereby to modulate said reradiated carrier Wave with a desired signal to be transmitted, means for receiving said reradiated carrier Wave and for deriving therefrom the desired modulation-signal components thereof, and means coupled to said lastmentioned means for utilizing said desired modulation-signal components.

15. A carrier-Wave communication system comprising, a transmitting station including means for generating and directly radiating a carrier Wave, a dipole antenna, a resonant transmission line coupled to said antenna and having an effective length equal to odd multiples of onequarter the nominal wave length of said carrier Wave to adapt said antenna to be responsive to said carrier Wave and to reradiate carrier-wave energy directly radiated thereby from said station, circuit-interrupting means coupled to said transmission line at the end thereof remote from said antenna selectively to open-circuit and shortcircuit the said remote end to cause said antenna respectively to reradiate and not to reradiate said directly radiated carrier-Wave energy, thereby to modulate said reradiated carrier Wave with a desired signal to be transmitted, means for receiving said reradiated carrier wave and for deriving therefrom the desired modulation signal components thereof, and means coupled to said lastmentioned means for utilizing said desired modulation-signal components.

- 16. A carrier-Wave communication system comprising, a transmitting station including means for generating and directly radiating a modulated carrier Wave, carrier-Wave radiating means remotely situated from said station and adapted to be solely energized by said carrier wave and thereby to reradiate carrier-Wave energy directly radiated thereto from said station, means for modulating said reradiated carrier Wave with a desired signal to be transmitted, means responsive both to said directly-radiated and reradiated carrier waves and dependent upon the modulation of said radiated carrier Wave for deriving the desired modulation-signal components of said reradiated carrier Wave, and means coupled to said last-mentioned means for utilizing said desired modulation-signal components.

17, A carrier-wave communication system comprising, a transmitting station including means for generating and directly radiating a carrier Wave frequency-modulated with a periodic modulating signal of approximately saw-tooth wave form, carrier-Wave radiating means remotely situated from said station and adapted to respond to said carrier wave and to reradiate carrier-wave energy directlyradiated thereto from said station, means vfor modulating said reradiaated carrier Wave with a desired signal to be transmitted, means for receiving said directly-radiated carrier wave and said reradiated carrier wave and for combining said carrier Waves to derive a signal of audible frequency modulated with said desired signal, and means coupled to said last-mentioned means for utilizing said signal of audible frequency.

18. A carrier-wave communication system comprising, a transmitting station including means for generating and directly radiating a carrier wave modulated by a first modulation signal, means for additionally modulating said carrier wave with a second signal to be transmitted to a remote point, carrier-Wave radiating means situated at said remote point and adapted to be solely energized -by said carrier wave and thereby to reradiate carrier-Wave energy directly radiated thereto from said station, means coupled to said carrier-Wave radiating means for deriving from said directly-radiated carrier wave the modulation-signal components thereof corresponding to said second signal and for utilizing said derived modulation-signal components, means for modulating said reradiating carrier Wave with a desired signal to be transmitted to a point remote from said carrier-wave radiating means, means situated at saidv last-named remotepoint for receiving said reradiated carrier wave and dependent upon that modulation of said directly radiated carrier wave which corresponds to said first modulation signal for deriving from said received reradiated carrier wave the desired modulationsignal components thereof, and means coupled to said last-named means for utilizing said lastnamed signal-modulation components.

19. A carrier-Wave communication system comprising, a transmitting station including means for generating and directly radiating a modulated carrier Wave having both amplitudemodulation and frequency-modulation components, one type of said modulation components comprising a signal to be transmitted to a remote point, means situated at said remote point and adapted to respond to said carrier Wave and to reradiate carrier-Wave energy directly radiated thereto from said station, means included in said last-mentioned means and responsive to said one type of modulation components for deriving and utilizing said signal to be transmitted, said means situated at said remote point also including means for modulating said reradiated carrier wave With a second signal to be transmitted, means for receiving said reradiated carrier Wave and dependent upon the other type oi said modulation components of said radiated carrier Wave for deriving from said received carrier Wave said second signal, and means coupled to said last-mentioned means for utilizing said second signal.

HAROLD M. LEWIS.

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

UNITED STATES PATENTS Number Name Date 1,771,148 Sprague July 22, 1930 2,169,374 Roberts Aug. 15, 1939 2,193,102 Koch Mar. 12, 1940 2,252,083 Luck Aug. 12, 1941 2,250,532 Hansell July 29, 1941

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