US2393414A - Modulation system for ultra high frequency waves - Google Patents

Description

' Jan. 22, 1945.

W.VAN B.- ROBERTS MODULATION SYSTEM FOR ULTRA HIGH FREQUENCY WAVES Fiied Sept. 25, 1942 4 6 IF 7 WAVE A 5/ 5/14 SOURCE v Vow/14E INVENTOR IKQTi/ Mm 6. Fauna.

ATTORNEY fluency er y,

Patented Jan. 22, 1946 2,393,414 I Museums SYSTEM toiiimnnmen FREQUENCY waves a yan Itg'berts, Princeton, "alg iassfignor toltadio Cor-poration of .Amei'ica a corporatiiin of Delaware Application September 25, 1942, seiiai 1%. 459,654

BCIaiins. (01.. 2511- -6 1 This invention relates to a method oi and apparatus for producing amplitude modulated ultra high frequency waves.

a As an i-llustratio rhjet us that as 10f a n i i eenit ri e iia hirequency waves the applicationiof a voltage increase of one of the operating-voltages oi the genera-tor causes an; increase iii-amplitude randalso an inc eas f r nqr, ln cs rdwee w h th i vention; the :output of "this generator is connected to a .wave radiating device; preferably of the electmmagnetic horn; type through a wave guide consisting ofahollow metalpipeg; By choosing the diameter-of this pipe sufficiently smallin comparison with the wavelength of theigenerator, the attenuation inthe pipe will decrease rapidly with increasing wave frequency pver'a particular range has been experienced in of frequencies; and this principle is employed in v the practice or the invention: There are, of

course, minimum ercritical frequencies for 'differeritv types. of .waves, below which they cannot existiin' and cannot be. transmitted through. the hollow pipe. Thus,- inthe'case assumed as' the -modu1ating voltage, increases; the amplitude of the waves fed-into the pipe: will increaseand sitain 'typesof high multaneously therewith there willi'-occur-an-;in-

creaseinxfrequency. The increase-in frequency eithe wavestimpressed upon-thewave guide (lecreasesrthei attenuation? j the 1 pipe so that the .Iwavesupon emerging-: from the: waveguide for radiation by the horn haveytheirr amplitude increased both by the-.factthat the inputamplitude was'increasedirandalso by the fact that the attenuatieninthepipewasd cr as d .The re sultin'g': radiationirom' the horn located at the remote. endiof the: pipe. is thus, amplitudemodulated: tea greatly increased extent; Itis, of course; also. frequency modulated but this fact is nine importance: whenth'e. radiated signals are to beirecei-ved i-nxa simple crystal; detector circuit of a-muiti-detection receiver." "I-herfirstdetectiun circuit" of such a: receiverffor the ultra high {relating voltage ior the ultra,h igh frequency GI'atOT-fiSfHGt the desired signal voltage but an intermediate frequency voltage which, in t'urn,

is modulatedeither asto amplitude or frequency e. s n volta In the foregoing illustration it was asst" that undesired frequency modulation stream-ti;

e ue av so rcewa .ieher ii y e iicfi. y a t m to am i ud n i ulet ihe me; It should heappreciated, however, that in the practiceof theinventionan ultra high .ffrequency' source may beemployed at the transmitter when has i iree en ym ulat d.d bm yir' i i b h h it pb il nwi l iud er ahi we :b aeh e ed; b empl i d me tubeassociated with said source ina manner .well

known in the art ofireguency modulation oi ps; i ons. iwha ar an men r i the practiee of thepresentinvention. V a

Fig. .1 of -the;drawing diagrammatically illus t-rates,- .by waypi example only, a transmitter em! bodirnent of the present invention, while Fig 2 iilustratesa receiver embodiment of the invention.

Referring to Ffg. 1 of the drawing, .there is shown a waveguide I in the, form of a metall-ic pipe having at one end an ltra high frequency generator Ziorimpressingyupon the pipe a frequency od t d-ul ra hi h qi ey Wave- The pipe I at the remote end is terminated by a suitable wave radiating structure 3,; here shown byway; of example as an electromagnetic hern. The pipe I is employed ior transmittingcerf irequency electromagnetic waves, sometimes called dielectric guidedwaves, pr0videdthe frequency of the waves; exceedsa certain critical cut-off frequency that is dependent on the type of wave, the transverse dimensions of thepipe and the dielectriccoeflicient of; the medium filling the interior of thet pipe e a i us t Q uid a es a e is i guished by their respective characteristic spacial distributionof the component electric and mag.

I netic fields and they may be represented as E and. H waves, as indicatedin the articles by G. C. Southworth and J. E. Carson et al., appearin in the April, 1936; issue of theBellSystem Technical Journals, Both of these articles disclose the critical relation that exists at cut-off. between frequency, dielectric coefi'icient and diameter of guide for each of the four principal types of waves That s, the macetransmitted through a hollow pipe of circular cross section.

In order to modulate the frequency of the ultra high frequency generator 2 in accordance with a signal voltage, there is preferably provided a source of relatively low radio frequency waves labeled I. F. wave source which is impressed nection with the drawing, the sole difference being that the waves pass through the frequency modulation to amplitude modulation converting pipe prior to being radiated in one case and after being radiated and picked up in the other case.

What is claimed is:

1. A system for, modulating the amplitude of ultra high frequency waves comprising a generator of said ultra high frequency waves, a wave guide in the form of a hollow conducting member, said generator being coupled to said Wave guide at one end for impressing a wave thereon to be transmitted therethrough, a wave radiator F in the form of an electromagnetic horn connected wave employed for transmission through the pipe.

This is because the greatest change in attenuation for a given small change in frequency occurs in the frequency region which is slightly higher than the cut-ofi frequency for all types of waves.

As an example of one practical construction which might be employed in the practice of the present invention, the pipe I might comprise a vertically arranged affair extending for a distance of several hundred feet in the air, with the bottom end coupled to the ultra high frequency generator whose frequency is to 'be modulated in accordance with signal potentials, and with the upper end of the pipe terminated by an electromagnetic horn radiating structure adapted to transmit signals in a desired direction and to a distance which increases with the height of the horn. The upper end of the pipe I in the example just given will most likely be curved so that the direction of emission of waves from the wave radiating horn will be horizontal. The wave guiding pipe, inthe example just given, may act as a self-supporting structure or be additionally supported by guy wires. Where the pipe is placed in a congested area where there are tall buildings, this pipe can be supported by the building structure. The pipe I may be as long as feasible and of a diameter of fifteen inches, by way of example, at which diameter the frequency of operation for a particular type of wave, assuming in this case an HI type of wave, would be in the vicinity of five hundred megacycles. Of course, for a different pipe diameter, the operating frequency will be different in inverse proportion.

Any suitable type of receiver can .be used in connection with the transmitting system of the drawing. As an example, such a receiver might comprise a crystal detector connected to an intermediate frequency amplifying and detecting I system adapted to select, amplify and detect the intermediate frequency wave impressed upon the ultra high frequency generator 2. Fig. 2 shows, by way of example, a receiving circuit for use in the invention, wherein the frequency modulated waves are received on an electromagnetic horn 3' connected at one end to. a suitable wave guide 1' which in turn is terminated at its other end in a detecting system utilizing a crystal detector.

It will be evident that the action of the wave to said guide at its other end, the diameter of said wave guide being so chosen with relation to the frequency of operation of said generator that the attenuation of the wave through said guide varies rapidly with respect to the frequency of said generator, and means for varying the frequency of said generator in accordance with modulating potentials.

2. A system for modulating the amplitude of ultra high frequency waves comprising a generator of said ultra high frequency Waves, a wave guide in the form of a hollow conducting member, said generator being coupled to said wave guide at one end for impressing a wave thereon to be transmitted therethrough, a wave radiator connected to said guide at its other end, the diameter of said wave guide being so chosen with relation to the frequency of operation of said generator that the attenuation of the wave through said guide varies rapidly with respect to the frequency of said generator, the frequency of said generator being slightly above the cut-off frequency of said wave guide, and means for varying the "frequency of said generator in accordance with modulating potentials. I

3. A system for modulating the amplitude of ultra high frequency waves comprising a generator of said ultra high frequencywaves, a wave guide in the form of a hollow conducting mem-' her, said generator being coupled to said wave guide at one end for impressing a wave thereon to be transmitted therethrough, a wave radiator connected 'to said guide at'its other end, the diameter of said wave guide being so chosen with relation to the frequency of operation of said generator that the attenuation of the wave through said guide varies rapidly with respect to the frequency of said generator, the frequency of said generator being slightly above the cutoff frequency of said wave guide, and means for varying the frequency of saidgenerator in accordance with modulating potentials, said modulating potentials being constituted by a radio frequency wave which is modulated by the signal to be transmitted.

4. A system in accordance with claim 1, characterized in this that said wave guide is a ver-' tically arranged pipe of at least several hundred feet in length and said horn is arranged to radiate waves from the-top of said guide in a substantially horizontal direction.

5. A system for convertingfrequency modulated waves to amplitude modulated waves, comprising a source of waves whose frequency is modulated, a waveguide, means coupling said' source to said waveguide at one end for impressing the frequency modulated waves on said guide for transmission therethrough, an elec-'- trical transducer coupled to the other end of said guide, the diameter of said guide being so chosen with relationto the frequency of said of a hollow conducting source that the attenuation of the waves through said guide for transmission therethrough, an elecsaid guide varies rapidly with respect to said frequency.

6. A system in accordance with claim 5, char-o acterizedin this that said wave translation system is a receiver including a crystal detector.

'7. A, system for converting frequency modulated waves to amplitude modulated waves, comprising a source of waves whose frequency is modulated, a wave guide in the form of a hollow conducting member, means coupling said source to said wave guide at one end for impressing the frequency modulated waves on said guide for transmission therethrough, an electrical transducer coupled to the other end of said guide, the diameter of said guide being so chosen with relation to the frequency of said source that the attenuation of the waves through said guide varies rapidly with respect to said frequency, the frequency of said source being slightly above the cut-off frequency of said wave guide.

8. A system for converting frequency modulated waves to amplitude modulated waves, comprising a source of ultra short waves whose frequency is modulated, a 'wave guide in the form member, means coupling prising a source of 'reactance tube modulator for varying the fresaid source to said wave guide at one end for impressingthe frequency modulated waves on trical transducer in the form of an antenna coupled to the other end of said guide, the diameter of said-guide being so chosen with relation to the frequency of said source that the attenuation of the waves through said guide varies rapidly with respect to said frequency, and a multidetection receiver having a crystal detector circuit for receiving the signals radiated by said antenna.

9. A system for converting frequency modulated waves to amplitude modulated waves, comultra high frequency waves, a

quency of said ultra high frequency waves in accordance with modulation potentials, a wave guide, means coupling said source to said guide near one end for impressing the frequency modulated waves on said guide for transmission therethrough, an electrical transducer coupled to the other end of said guide, the diameter of said guide being so chosen with relation to the frequency of said source that the attenuation of the waves through said guide varies rapidly with respect to said frequency, the frequency of said source being slightly above the cut-off frequency of said wave guide.

WALTER vm B. ROBERTS.

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