US2419135A - Ultra high frequency amplifying system - Google Patents

Description

April 15 1947. c. w. HANSELL ULTRA HIGH FREQUENCY AMPLIFYING SYSTEM Filed Au 20, 1942 57:32 4 530m Qz mwjabnz 55:02.

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N25055: IIAI INVENTOR CLAREN Patented Apr. 15, 1947 i i V V UNITED STATES .poration of Delaware 'Glarence W. Hansell, Port Jefierson, N. Y., assignor to Radio Gorporation of America, a cor- Application nugus zo, 1942, Scrial No. 455,443

V 3 Claims. 1

This invention relates to ultra high frequency amplifyingsystems and has for its object the provision of means for increasing the .power level of ultra high frequency currentain a manner which will result in stable operation and large power gain in the amplifier, when the frequency of the currents to be amplified is very high. The inventlon is a result "of study and development of ultra high fre'qency radio relaying systems but it is capable of much wider application than in the field of radio relaying alone.

It has been found that when radio communication is attempted at higher and higher'carrier frequencies a frequency may be reached at which vacuum tube amplifiers are no longer capable of providing amplification but require more input power than the power output. Most commercial vacuum tubes 'now available lose their ability to amplify at frequencies ranging from 20 to 100 megacycle's, depending upon the design "of particular tubes. Special tubes have been developed, on an experimental basis, which are capable of supplying a low ratio of power amplification at frequencies as highas about 500 megacycles but the number "of these tubes which would be required in cascade to give asmu'ch amplification as is required for many purposes 'woul'd be excessive and the difliculties in sup'press'ii'ig modulation distortions during amplification would be, for all practical purposes, insurmountable.

Even in ultra high frequency superhet'ero'clyne receivers where high frequency amplification ahead of the first detector would be very desirable, it has' been the usual practice to omit the amplification ahead of the first detector, according to my experience, when the'reeeived carrier frequency is 100 megacycles or more. This is because of the extreme diffieulty encountered in attempting "to "obtain power gain and amplifier stability at such high carrier frequencies.

My present inventicn recognizes this frequency limitation in vacuum tube amplifiers and provides a means by which stable amplification may be obtained with any type of tubes at frequencies higher than could be obtained before.

In carrying out my invention I provide means for beating or heterodyning input currents of ex tremely high frequencies down to some lower frequency at which high power amplification can be obtained with available vacuum tubes. I then amplify and frequenc multiply the lower frequency power in a chain of amplifiers similar'to that described in my U. S. Patent No. 2,032,208, granted February '25, 1936.

iBy this means I obtain large :overall power -am-:

plifi'cation in a system which is relatively stable and obtain an output power, which is very much greater than the input .power, at an output carrier frequency of the same order of magnitude as the in'put carrier frequency.

A further very important refinement of my invention permits its use for amplifying and'radio relaying at the "same carrierfrequency as'taught in my S. Patent "No. 2,250,532, dated 'July '29, 1941; No. 2,183,562, dated December19,- 1939-; -No. 2,229,078, dated January 21, 1941; and No. 2,280,822, dated Apri'123, 1942.

In applying this feature or'refinement of "my invention "I provide means "to amplify and to irequency -multiply a. portion of the power existing in the main amplifier system to obtain power at a very high frequency which differs from the input frequency by an amount substantially equal tothe beating or he'terodyne frequency in them;- put of the detector. '1 then use this very high frequency power to control, or synchronize, the beating oscillator for the heterodyne detector and, in consequence, give the main amplifier output carrier frequency a fixed, or locked, or sync'hronous relationto the carrier frequency of the input p wer.

To illustrate "my invention I have used block diagrams representing various combinations of apparatus for carrying out my invention. In each instance I have indicated the functions to be performed by each piece of apparatus. Some of these functions and certain of the meansfor carrying out each function are already so well knownand so commonly used in the radio com mum-cations art that detail showing and explanation of :each piece would only confuse the dis closure of my invention. :1 will omit "detail descriptio'ns of certain parts of the equipment used to carry out the several indicated functionsiand describe only those which-need description.

In describing my invention in detail reference will be made to the attached drawings wherein the single figure illustrates by rectangle 'a high frequency amplifying system arranged in accord* arice with my invention.

Reference will also be made to the table on page '7 wherein is shown the relation of the frequencies of various waves used in my relay amplifier, such as, the input wave, local oscillations used in hetero'dyning, intermediate frequency wave, intermediate frequency wave as multi'p lied, and output wave. This table gives the possible rreduencyrelaticns "for repeating without changing the degree or percentage of carrier wave frequency modulation.

In the figure I have shown by rectangle an amplifying system in four cooperating parts. In unit 2 of these parts is an oscillator which supplies oscillations for beating in unit 4 with a high frequency current fed to the circuits in unit 4, which is to be amplified and repeated at the same frequency or at some other frequency which bears a definite relation to the frequency of the input current. Power from the oscillator and input power to the system are combined in a heterodyne detector in unit 2 and cause an output from the detector at frequencies equal to the difference between the oscillator frequency and the input frequencies. A portion of the output power from the heterodyne detector in unit 4 is multiplied in frequency and preferably increased in power in a synchronizing frequency multiplier and amplifier in unit 6. Output power from the synchronizing frequency multiplier and amplifier is then utilized to control or synchronize the heterodyne oscillator in unit 2. As a result, the beat frequency output from the heterodyne detector in unit 4 is fixed at a definite sub-multiple of the input power frequency in the same manner as in the system described in Osborne U. S. Patent No. 2,039,657, dated May 5, 1936.

The difference frequency is also supplied from unit 4 to the power amplifiers and frequency multipliers in unit 8 and thence to lines or radiating means.

A detail requirement in setting up the system must be met if the system is to be stable. This requirement is that, when the incoming carrier wave, F1, is decreased in frequency by the modulation then the intermediate frequency carrier wave F2 must also be decreased in frequency and vice versa. When this requirement is met any variation in frequency F2 reacts on frequency F4 in a direction to oppose or limit the variation in F2. Unless variations in frequency F2 do react through F4 to reduce themselves the system is unstable and inoperative. That is, if a variation in F2 varies Frin a direction to increase the variation in F2 still more then the variation will be unstable and will continue until F2 has gone to or infinity, or as far a frequency selectivity of the coupling circuits in the system will permit. We may obtain the desired stable condition by operating the synchronized heterodyne oscillator always at a lower frequency than the input carrier wave frequency. This is the condition'which I would use in practice.

Considered from a different viewpoint, one may assume that the combination of units 2, 4 and 6 forms a frequency divider. Unit 8 forms a frequency multiplier. If the ratios of frequency division and frequency multiplication are alike, so that the final output frequency is equal to the input frequency, then it should be apparent that there is no change in degree of fresignal current through the system. The frequency deviations due to modulation remain a constant percentage of the carrier current as we go through frequency dividing and frequency multiplying processes but, of course, a constant percentage deviation gives a different absolute deviation, in cycles per second, in proportion to the carrier frequency.

Another portion of the output power from the heterodyne detector is frequency multiplied and amplified to relatively high power in a frequency multiplier and power amplifier equipment similar to that described in my U. S. Patent No. 2,032,208. Output from the frequency multiplier and power amplifier equipment then provides the final output from the whole amplifier or repeater system of my invention.

t will be understood by those skilled in the art that frequency selectivity wil1 be present in the various circuits in the four units combined to form my invention. This frequency selectivity results automatically. from the necessity to tune the circuits to some frequency in the band of operating frequencies of each'unit. In addition, I may employ additional frequency selectivity in ways well known in the art or I may employ various known methods and devices for obtaining more nearly any desired amplitude and phase response to various frequencies in a band of frequencies to be passed through the system.

A Very great virtue of the system is that a large portion, if not all, of the power amplification in the system may be obtained in vacuum tube amplifying devices which operate at relatively low frequencies and which, therefore, can provide amplification which might be, and frequently has been, unobtainable at frequencies corresponding to input and output frequencies of the system.

In addition I obtain all the advantages of stable operation and freedom from feedback in the amplifier chains described in the system of my U. S Patent No. 2,032,208. I

Usually, I would expect to obtain output from my system at the same frequencies as exist in the input but this is not necessarily the case. I may employ different ratios of frequency multiplica. tion in the frequency multiplier and amplifier units such that a given band of input frequencies may result in any one of a considerable number: of choices of output frequency bands.

In practice I prefer to use frequency multiplier stages which have a rather low ratio of frequency multiplication, such as 2:1 or 3:1, particularly in the multiplier and amplifier equipment which produces the final output power. This is because the efiiciency and power. gain of a frequency multiplier stage decrease with increasing ratio of fre-.

quency multiplication.

If it is assumed that only frequency doubling or tripling stages are used, then the frequency relations existing in the system may be such as those shown in the examples given below:

F1/F2 ilk/1f: Possible Ratios F /F assuming only amplification, doubling or tripling 2 1 1/2 1 3/2 2 3 4 9/2 6 8 I 9 12 2 5 3 2 l/3 2/3 1 4/3 2 8/3 3 4 16/3 6 8 13 3 273 4 3 l/4 l/2 3/4 1 3/2 2 9/4 3 4 9/2 6 27/4 8 5 4 1/5 2/5 93/5 4/5 6/5 8/5 9/5 12/5 16/5 18/5 24/5 27/5 32/5 3 2 it ii?- it it 6% it 3/? 12 ,7 6? 3 4 9/2 16/3 I l 7 18 7 24 7 27 7 3 3 7 1/8 l/e 3/8 1/2 3/4 1 9/8 3/2 2 9/4 3 27/8 4 quency modulation in going through the whole system.

If they output frequency is not the same as the input frequency, then there will be a change Obviously, many other frequency relations may be used. In particular, it is probable that I may employ other than doublers or triplers in the relatively low power level synchronizing frequency in frequency modulation deviation in'passing the multiplier and amplifier equipment for syn- 5 hronizing the heterodyne; oscillator. In fact, in this equipment I would expect to employ a minimum number of stages by using the-highest-frequency multiplying ratios possible, or practical, to obtain sufficient final power output to control the heterodyne oscillator.

To illustrate one possible application of my system I may suppose that 'a' directional receiving antennais employed to pickup radiated power from a distant radio transmitter which transmits a carrier wave at 900megacycles per second, frequency modulated by meansof television signals having frequencies extending from or near 0 to 3,000,000 cycles per second. The inputpower would then extendover a band from 897' to 903 megacycles per second.

In theheterodyne detector I may reduce the carrier frequency to 100 megacycles per second with a band of frequencies due to modulation extending from 97 to 103 megacycles per second. I may then multiply the detector output carrier frequency up to 800 megacycles and oscillator carrier power at this mean frequency may beat with the incoming signal power in the heterodyne detector. At the same time, I may multiply the detector output frequency, greatly increasing the power at the same time, up to any one of a series of frequencies to provide the output power from the whole system. If I limit the frequency multiplication per amplifier stage to 2:1 or 3:1, then the final output frequency might be 100, 200, 300, 400, 600, 800, 900, 1200, 1600, 1800, 2400, 2700,

3200, 3600 megacycles and so on.

In a preferred arrangement the 900 megacycle input power carrier, and its side band frequencies, will be reproduced with the same frequencies but at much higher final output from the whole system. The arrangement of the example would be potentially useful for radio relaying of television or any other type of signals, transmitted through a chain of geographically separated repeater stations, all operating on the single frequency modulated 900 megacycle carrier wave.

As another arrangement I may assume that it is permissible to employ frequency multiplier stages with multiplication ratios of 5:1 in the synchronizing frequency multiplier and amplifier, since relatively small power gain is required in the frequency multipliers of this unit. Then we might repeat a 600 megacycle frequency modulated carrier wave without change of frequency or depth of modulation, but with large increase in power, by employing a synchronized oscillator mean frequency of 500 megacycles and a detector output mean frequency of 100 megacycles.

As a still further example, I might repeat a 1600 megacycle modulated carrier wave by employing an oscillator frequency of 1500 megacycles and a detector output frequency of 100 megacycles. In this case the synchronizing frequency multiplier and amplifier would preferably contain one stage with a frequency multiplication ratio of 5:1 and another stage with a ratio of 3:1. The frequency multiplier and power amplifier would contain four frequencydoubling stages and perhaps one or more amplifier stages without frequency multiplication.

Of course, in practice there may be variations in the detail arrangements for applying my invention. For example, the heterodyne detector unit may contain amplifiers of the beat frequency output before energy is taken out to the two frequency multiplier and amplifier units. Also, in some cases when proper frequency relations are chosen there maybe frequency multern. In other words, over a wide range of input power the output power from each'of the two frequency multiplier and amplifier units should remain constant. This is particularly important when my repeater system is employed as part of a long chain of repeaters between which undesirable variations in transmission. eificiency may take place.

In itsessence 'my invention is a method and means for amplifying or repeating frequency modulated carrier currents of extremely high frequency which comprises beating the currents down to a lower frequency current which is in locked sub-multiple frequency relation to the original current and then frequency multiplying and amplifying the lower frequency current up to the original frequency, but at higher power level than that of the original current.

I claim:

1. The method of relaying frequency modulated high frequency wave energy which includes the following steps, receiving said high frequency wave energy, beating the same with other wave energy of lower frequency to derive correspondingly modulated wave energy of a difference frequency which is a submultiple of the frequency of the received wave energy, amplifying the beat frequency energy and multiplying its frequency by a factor such that the said frequency multiplied wave energy is of the same frequency as the frequency of said first wave energy, transmitting energy resulting from the last step, and locking the transmitted energy in fixed frequency relation with respect to the received wave energy by multiplying the frequency of the derived wave energy of said difference frequency by a factor such that the multiplied frequency differs from the frequency of the received wave energy by said difference frequency and entraining said other energy with said last mentioned energy of multiplied frequency.

2. The method of relaying frequency modulated high frequency Wave energy which includes these steps, receiving said high frequency wave energy, beating the same with other wave energy of lower frequency to derive correspondingly modulated wave energy of the difference frequency which is a submultiple of the frequency of the received wave energy, multiplying the frequency of said energy of said difference frequency by a factor such that the wave energy of multiplied frequency is of the same frequency as the received wave energy, transmitting the wave energy of multiplied frequency, and locking the transmitted energy in fixed frequency relation with respect to the frequency of the intercepted wave energy by multiplying the frequency of the derived wave energy of said difference frequency by a factor such that the multiplied frequency differs from the frequency of the, received wave energy by the said difference frequency and entraining said other wave energyv of lower frequency with the last mentioned wave energy of multiplied frequency.

3. In a relaying system, connections for re ceiving frequency modulated high frequency wave energy, amixer system including a source of oscillations of a frequency lower than the frequency of the received wave energy for changing said modulated wave energy to wave energy of multiplied thereby to a frequency which differs from the frequency of the received energy by said lower frequency and a coupling between said last named frequency multiplier and said source of oscillations to lock said modulated wave energy of lower frequency being amplified and frequency multiplied in fixed frequency relation to the frequency of the received and retransmitted wave energy.

CLARENCE W. HANSELLU REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,032,208 Hansell Feb, 25, 1936 2,039,657 Osborne May 5, 1936 2,124,191 Geiger July 19, 1938 2,180,816 Miller Nov, 21, 1939 1,822,086 Falkner et al Sept. 8, 1931 2,369,268 Trevor Feb. 13, 1945 2,000,130 Espenschied et a]. May '7, 1935

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