US2064582A

US2064582A - Radio apparatus

Info

Publication number: US2064582A
Application number: US750791A
Authority: US
Inventors: Wolff Irving
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1933-08-31
Filing date: 1934-10-31
Publication date: 1936-12-15
Anticipated expiration: 1953-12-15

Description

I. WOLFF RADIO APPARATUS v Dec. 15, 1936.

` Filed oct. s1. 1934 sss ilalleli.

Patented Dec. l5, 1936 UNITED STATES PATENT OFFICE mio APPARATUS Delaware Application October 31, 1934, Serial No. 750,791

19 Claims.

This invention relates to radio apparatus and particularly to a method of and a device for modulating radio frequency energy of ultra high frequency.

It is known that a beam of radio frequency energy may be modulated by modulating an ionized gas through which the beam is projected. In a copending application, Serial No. 687,544, filed August 3l, 1933, by Ernest G. Linder, it was shown that gaseous discharge tubes of one type or another might be interposed in the path of a radio frequency beam for modulating theamplitude thereof. Linders device is an improvement over other modulating systems in that amplitude modulation of ultra high frequencies may be obtained quite independently oi disturbing effects upon the carrier oscillator. The amplitude modulation is also accompanied in greatly reduced degree by frequency modulation. It has, however, been found somewhat diiiicult in all cases to obtain suflicient freedom from objectionable frequency, or phase modulation. The phase modulation is caused by variations in the index of refraction of the gaseous medium in a single tube through which the radio beam is projected. The index of refraction, in turn, is a function of certain absorption and reflection characteristics the importance of which will presently be discussed.

It is among the objects of my invention to provide modulating means to be used in connection with an ultra high frequency radio energy generator, which means shall be relatively free from phase modulation when amplitude modulation alone is desired.

It is another object of my invention to provide means of the character hereinbefore suggested in which frequency modulation may be had to the substantial exclusion of amplitude modulation. if such is desired.

A still further object of my invention is to provide an improved method of and means for modulating ultrahigh frequency radio energy in Y such a manner that 'distortion of the desired signals may be eiectually avoided, even when a high percentage of modulation is obtained.

In carrying out my invention, I preferably employ two distinct zones of ionized gas, the characteristics of these zones being so suitably differentiated from one another as to compensate for either the absorption or the refraction effects inherently present in these ionized zones.

The various objects, features and advantages of my invention will best be understood upon reference to the following detailed description when taken in connection with the accompanying drawing, in which Figure 1 shows schematically one embodiment of a radio transmitter having a modulating system comprising a plurality of gaseous discharge devices for intercepting the path of a radio beam,

Fig. `2 is a plan view of the gaseous discharge tul'es otherwise shown in perspective in Fig. 1, an

Fig. 3 is another plan view showing a modiiication.

The embodiment of my invention as herein shown for illustrative purposes in Figs. 1 and 2 comprises preferably a generator I adapted to produce oscillations of ultrahigh frequency, the wavelength of which is of the order of a few centimeters, or less. The oscillations thus generated may be impressed upon and radiated from an antenna 3. A parabolic reector 5 may be 2 used for directing the radio beam in the direction of a receiver (not shown) to which it may be desired to transmit signals.

For intercepting the radio beam and for providing modulations thereof I preferably employ a gaseous discharge tube 1 having a thickness a. Another gaseous discharge tube 9 having a thickness b is also employed. The gaseous contents of the tubes 1 and 9 respectively may be differentiated from one another both as to kind of gas and as to pressure. The voltage impressed across the electrodes of these tubes may also be differentiated in the one case from that in the other. For this purpose the conductors II are connected at diierent points to the source of direct current I3 so that the voltage drop in the tube 1 may be greater than that in the tube 9. The connections may also be interchanged, if desired. Other electrodes of the tubes 1 and 9 respectively are connected to the secondary I5 of a transformer Il having a primary which receives energy from any suitable modulator, such as telephone transmitter I9. The secondarir winding I5 has a mid-tap 2l which is connected back to the battery I3 for completing the modulator circuits.

It will be noted that the gaseous discharge tubes 'I and 9 are suitably connected with the secondary winding I5 for operation in a pushpull manner.

Because of differences in the absorption and refraction characteristics of the two tubes 1 and 9, it is possible to obtain amplitude modulation without appreciable phase modulation, or vice versa. II amplitude modulation alone is desired,

then the phase modulation in the tube 1 is caused to neutralize the phase modulation in the tube 9. If frequency or phase modulation is desired, then the amplitude modulation in the tube 1 is caused to neutralize the amplitude modulation in the tube 9. How this is accomplished may be best understood by a mathematical consideration of the factors involved.

Let f represent the carrier frequency radiated b'y the antenna 3. The index of refraction (no) of the unmodulated gaseous medium such as that in one of the tubes 1 and 9 may be compared with the nal index of refraction n when the gaseous medium is subjected to modulation, Let d represent the length of the ionized gas path (in centimeters) through which the radio frequency beam Vis tobe projected. The time for the radio frequency wave to 'get through this path is:

dna

where c equals the velocity of light. In the case of the tube 9, d becomes du due to the thickness of the tube as shown, and in the case of the time for the ray to get through the tube 1, d becomes da. Ineither case when the modulation occurs, the time to is changed to V Combiningvthese equations,

' ing voltages.

Thek phase shiftdue to modulation, therefore, equals- 1 T01-n0) y Tf which reduces to 4 g-dQ-'l-llo) where A is the wave length in air.

Under practical conditions, assuming that it is desired to transmit a radio frequency beam having a wave length l i=`1 centimeters,

it is quite possible that (nflml-would equal .5,

also d lwould be of the order of 20V centimeters and the phase shift with amplitude modulation would amount to somewhere in the neighborhood of 21|-, which 'would be very apt to produce unbearable distortion ofthe signals in certain types of receivers. Thisphase shift, however, maybe reduced to negligible proportions by taking any one or more of a4 number of steps tending to produce differential'characteristics in vthe two tubes l and 9, whereby the indices of refraction may be caused to differ from one another in marked degree. v

Thus, the ratio of tube diameters to one another while in the other tube the absorption fa'ctor would be predominant. If frequency or phase modulation is the object then the refraction characteristic is made to predominate while the absorption characteristic of the two tubes is made to neutralize.

Both the absorption characteristics and the index of refraction are dependent to a certain extent upon the nature of the gaseous medium. It has been found that a gas changes its absorption and index of refraction for electromagnetic waves when its degree of ionization is changed. Accordingly, I have found, for example, that the desired differences in characteristics of the two tubes 1 and 9 may be obtained by employing neon in one and argon in the other. A mercury pressure of .04 millimeters has also been found satisfactory. I do not intend, however, to be limited in carrying out my invention to any particular gaseous content of the tubes, nor to the Working pressure thereof, as here given.

Absorption ofthe radio frequency wave as it passes through the gas is caused mainly by collisions made by the free electrons with ions, molecules, or against the tube Walls. The effective collision frequency is determined largely by the kind of gas, the amount of impurities present, and the pressure. Under certain conditions, a small amount of impurities may change the factor of collision frequency, and hence change the absorption factor, many fold.

'I'hc phase change is due primarily to the number of free electrons or ion density in the gas. For optimum results it has been found best to rst provide suitable differences in the characteristics in the tubes 1 and 9 in accordance with the foregoing teachings and th n to vary the difference of potential applied o these two tubes through the conductors Il so as to provide suitable compensation between the respective indices of refraction of the ionized gases therein for substantially neutralizing the phase shift caused by one tube in comparison with that caused by the other. The optimum conditions may be readily obtained by adjusting the relative ionizing voltages.

It will be clear from theforegoing disclosure that the radio frequency Wave must pass through the tubes 9 and 1 successively. As shown in Fig. 1, the two tubes have different voltages impressed thereon. These voltages may, however, be equalized if necessary in order to produce neutralization of phase shift caused by modulation potentials. When the current in one of the tubes is increased, that in the other is decreased due to the push-pull arrangement of the circuit connected through the secondary winding I5. The tubes 1 and 9 themselves being characteristically different, the applied alternating current voltage generated in the secondary I5 may be caused to produce amplitude modulation on the radio beam while the phase modulation is balanced out.

It will be noted that the contra-phasal impress of modulating voltage upon the two tubes 1 and 9 possesses a still further advantage. If either or both of the tubes `is found to possess a non-linear relation between the absorption characteristic and the impressed modulating voltage, it doesnt matter. The push-pull operation of the two tubes causes the non-linearites themselves to be substantially balanced out.

Referring to Fig. 2, i-t is shown that the path of the radio frequency beam may be made longer through tube 'I than through tube 9 in order to effect differences in the degree of absorption. In

.while substantially suppressing phase modulathis case the cross-sectional diameter a is greater than the cross-sectional diameter b. In Fig. 3, however, the same eifect may be obtained while using two tubes of the same cross-sectional diameter. In this case additional vertical sections are provided and by staggering the sections in two planes the effective thickness dimension a, which represents the path of the radio beam through the tube 8 is adjusted to a suitable value.

Although I have disclosed herein certain speciflc means for accomplishing the objects of my invention, these are given merely by way of-example and are not to be construed as limitations to the scope of my invention. Other modifications will suggest themselves to 'those skilled in the art, and my invention, therefore, is not to be limited except insofar as is necessitated by the prior art and by the spiritof the appended claims.

I claim as my invention:

1. A radio transmitting system including a carrier wave radiator, a plurality of gaseous discharge devices in the path of radio frequency.

waves projected vfrom said radiator, said devices having differentiated absorption and` refraction characteristics, and means for producing amplitude modulation of said radio waves and for simultaneously minimizing the phase modulation thereof, said means comprising apparatus for impressing modulation energy simultaneously upon said gaseous discharge devices, and contraphasally on two portions thereof.

2. A system in accordance with claim 1 in which the gaseous contents of said discharge devices are chemically differentiated from one another, asbetween respective devices.

3..,A system in accordance withclaim 1 in which the gas pressure in one of said discharge devices differs from that in another.

4. A system in accordance with claim 1 in which one of the gaseous discharge devices has dimensions and shape which present a longer path of travel for said radio waves when projected therethrough than is provided by another of said discharge devices.

5. 'A system in accordance with claim l and including means for impressing across the electrodes" of one of said gaseous discharge devices an ionizing potential greater than that which is applied across the electrodes of another of said devices.

6. A system inaccordance with claim 1 in which one of the gaseous discharge devices possesses greater ion density than is possessed by another of said devices.

7. A system in accordance with claim l in which one of said gaseous discharge devices possesses greater absorption characteristics with respect to radio frequency wave energy than is possessed by another of said devices.

8. A system in accordance with claim l in which one of said gaseous discharge devices possesses greater radio frequency wave refraction characteristics than is possessed by another of said devices.

' 9. Inra device of the class described, a source Vof radio frequency carrier Wave energy, a source of signal modulation energy, `a plurality of gaseous media disposed in the path of said radio frequency carrier wave energy. and means including a push-pull network for so controlling the ionization of said gaseous media differentially in` response to variations in said 4modulation energy that amplitude modulation of said radio frequency carrier wave energy is` obtained tion thereof.

10. In a device of the class described, a source of radio frequency carrier wave energy, a source of signal modulation energy, a plurality of gaseous media disposed in the path of said radio frequency carrier wave energy, and means including a push-pull network for so controlling the ionization of said gaseous media differentially in response to variations in said modulation energy that phase modulation of said radio frequency carrier wave energy is obtained while substantially suppressing amplitude modulation thereof.

ll. In a device of the class described, a gaseous discharge tube adapted to be interposed in the path of a directed radio beam for modulating the same, said tube having non-linear refraction characteristics in relation to variations of ionizing voltage impressed across its electrodes, a second gaseous discharge tube adapted to be simultaneously interposed in said path, said tube having non-linear absorption characteristics in relation to variations of ionizing voltage impressed across its electrodes, and means for modulating the energy amplitude of said radio beam in response to modulations of ionizing voltage impressed contraphasally upon the two said tubes.

l2. In a device of the class described, a pair of gaseous discharge tubes adapted to be interposed in the path of a directed radio frequency beam for modulating the same, one of said tubes having a greater ratio of absorption of said radio beam per volt of impressed modulation voltage than the other oi said tubes, each of said tubes having opposite indices of refraction, and means in combination with said tubes for contraphasally impressing thereon modulations of an ionizing voltage, whereby the ratio of absorption and the index of refraction is increasing in the first tube when the index of refraction is decreasing in the other of said tubes.

13. In a radio transmitting system having a source of directed radio frequency carrier wave energy and a plurality of raried gaseous zones intercepting the path of said energy, the method of producing amplitude modulation of said energy which comprises providing suitably dinerentiated conditions of ionization in one of said gaseous zones with respect to another of said gaseous zones, producing a glow discharge in each of said zones,lvarying the drop of potential along the path of said glow discharge in each zone in accordance with a signal by which said radio frequency carrier wave is to be modulated,`

and simultaneously controlling variations of the absorption and the refraction characteristics in respectively diierent gaseous zones in such manner that phase modulation of said carrier wave energy is substantially suppressed.

14. The method of modulating a radio frequency wave which comprises projecting the radio frequency wave through a pair of gaseous discharge paths, changing the absorption characteristic of one of said paths, and contraphasally changing the index of refraction of the irst and second of said-paths to said radio frequency wave in accordance with signal currents.

l5. The method of modulating a radio frequency wave which comprises projecting the radio frequency wave through a pair of gaseous discharge paths, changing the index of refraction of one of said pairs to said radio frequency wave, and contraphasaliy changing the absorption characteristics of each of said paths to said Vradio frequency wave in accordance with signal curren 16. The method of modulating the phase of a radio frequency wave vwhich comprises projecting the radio vfrequency wave through a pair of gaseous discharge paths, varying the index of refraction of one of said pathsv to said radio frequency wave, and contraphasally varying the absorption characteristics of each of said paths to said radio frequency Wavein accordance with signal currents.

17. The method of modulating the amplitude of a radio frequency wave which comprises projecting the radio frequency wave through a pair of gaseous discharge-paths, varying the absorption characteristic of one of said paths to said radio frequency wave, and contraphasally varying the index of refraction of each of said paths to vsaid radio frequency wave in accordance with signal currents.

18. The method of modulating the phase of a radio frequency wave which comprises projecting the radio frequency wave through a pair of gaseous discharge paths. varying the index of refraction of one of said paths, and neutralizing any change in the absorption characteristic of the last mentioned path byoppositely varying the absorption characteristic of the other path in accordance with signal currents.

i9. The method of modulating the ampntude 1 of a, radi'o frequency wave which comprises projecting the radio frequency wave through a pair of gaseous discharge paths. varying the absorption characteristic of one of said paths, and neutralizing any change in the index of refraction of the last mentioned path by oppositely varying the index of refraction of the other path in accordance withl signal currents.

IRVmG worm.-