US2228692A - Load stabilizing means for modulation systems - Google Patents

Description

Jan. 14, 1941. DAWES 2,228,692

LOAD STABILIZING MEANS FORv MODULATION SYSTEMS I Filed on. 14, 1958 I 5mm 'GOIIIZQIL. I

Patented Jan. 14,1941

mtmioaielsrs generally systems and l v devices formodulating radlo= frequency energy and,more particularlwtosystems in whichenergy 1 '1 f, modulated at difierent frequencies issupplied to 5 separate loads; y r.

V Inthe operationo'i systems oi thetypereferred to differently-modulated. energy" may be supplied to two antennas forlrthe purpose or radiating two 1, differently modulated fieldswhich' overlap to provide-an equi signal zone which may beused as a guidance beaconforaircraftr If the tworadiated fields are characterized,- by tdifierent modulation frequencieait is usual, practise-tosupply each of the ,twoxradiatmgg antennas with radio ,frequency '15 i energy from a common source, rnodulating means I being interposed qlbetweenwthe' source and each i antenna n sls ne a fl t e type w a mechanical modulators ,Itf has 'beena foundpthat.{in systems" the "2'0 :ener'gizi'ng' current each go f the antennas will vary from; zer to a maximum, ,suchva1iation bein t h n ina re' u n k1W3 variation of the power in the load, will icausere ltidnin the tank tcircuit supplying; the antennas, fsuch "25 regulation being also attire modulatingfrequency.

Inasmuch as the second antennais supplied with ;-radio' irequency energy fromthesouicernodulated :at a, second frequency it will be apparent that regulation will also occur thej'input circuit at l 30 this secondflfrequeney Thusl the energyfsupt J plied toeach antenna is modulatedjnovonly at the intended frequency but also,1anddue to the Q regulationin the input circuit due' totheniodulation of the energyisuppliedto theotherj antenna, 35 atj'the modulationf irequency of the energy suppliedto the other antenna. This eflect'is known ,as cross niodulation and in order as decreas'eor do "away with this 'efi'ect it the usualpractise to t operate'thesystem at a. low fraction of its possible output inorder to increase the ratio of the power in theinput-circuit to thepower drawn bysthe antennas-1 1 i it l I havefound that such or oss-modulation; may i lbe efiectively"decreased or entirely prevented by providing 'iwitheach antenna anon-radiating load which is suppliedwith power in a varyingamount which is equal rat' anytime totlie difference. be-

tween the load: -current drawn by the l associated antenna and the instantaneous value. of "the current drawn by the antenna. 11,'I'hu s, the

1 dummygloadwill beconnected with the modulator in such a manner that, when the full power of the input'clrcuit is supplied to the antenna, no power is. supplied to the dunimy;1oad,,this ratio. then lggwch'anging constantlytthrcugh equality-until full PATENT-.2FFICEJ: t 1

mm srABmzINGMEANs-Forr W MQDULA'IION SISTEMSJ; l r H GomerflLDavies; ,Wood side,"Mdaffassignor I flwashingtonglnstitute of 'Technology,-'Inc'.,- WWnmEP -w sme i s s mmer t 3 Applicationbctobenld, 1938, Serial No. 235,019 i her the entire Po sible poweroutput of the-source may be morenearly employed.

i i In prior artsystems, in which means-aecording Itothis invention are not employed, and in which the :maximum power requiredto be-suppliedhto each antenna is, for example, 50 watts, (33 watts carrier,j100% modulated) it has been necessary totprovidega source having a possible power output of approximately 400 watts, ,the excess, or 300 watts, providing no useful purpose but beingnec- ,essary inordervtomaintain the: required large. I ratio offpower'in theinput circuit topower inthe -1oad circuit In systems --employin'gthe-present invention it is, of course, not-possibleto utilize the entire'power of the source in theantennas due to the power:absorbed-by the dummy loads, but the maintenance .of t a. constant load on thesource permitsa much larger fractionaof. thepower of 1 it thesource to be applied to the useful loads] a It.is,accordingly;the object oftheinventionto provide an electrical system for supp1yi ng-m0du- "lated radio frequency energy from a source. to 7 l twoor more loads, such as antennas, which system 7 include-means -for maintaining a constant a load on the source, of power, thus preventing a crossmodulationl. a

xqOther objects-and features -of noveltywill be apparent from the following description. andthe appended drawing, it being understood, however, lthatl-such description and drawing are only illustrative oithe invention, which is not limited in a 1 way thereby or "otherwise thangby, the zip-"40 pendedclaims.

1 The single figure of the drawing is a diagran'r illustrating a beacon system incorporating means according to the invention.

In the single figure of the drawingthere is matrated a beacon system eniployingfth'e load stabilizing means of the present invention. In this 7 systema tank circuit I, whichiorms'theffinal stage of a source of radio irequencyenergy, isconnected to supply energy to two useful loads 2," 3 which; maybe antennas adapted'to radiate fields winch overlap to provide .anequi-signal 'zone which may be used asa guidance 'means for aircra ft, .-The outputcoil 4 of the tankicircuit :is

coupled to two coils 5, 6. Each ofthese coils is connected to supply energy-to one of the useful loads,modulating means being connected between each of such coils and associated useful load in order that the radio frequency energy in each such useful load will be modulated at a character istic frequency. l v

One of theoutput terminals of coil 5 is -connected to two shielded transmission lines'lfl, 'II and the second terminal of the coil is grounded at I! through the shields of the two lines. The line H is connected to supply current to the useful load 2, while the second transmission line lll' isconnectedto supply current to a dummyload l3] the purpose of which will be made apparent hereinafter.

Mechanical modulating means are'connected in the transmission lines H), II in order to impress a characteristic modulation on the .radio frequency energy supplied to thetwo loads. Such means -comprise a rotary capacitor including the two stator plates l4,w|5, which are connected, re-

spectively, to the transmission lines l0, ll by shielded transmission lines I6, l1, and-a rotor I8 which is grounded at H! and which has plates at the opposite ends thereof which pass over .the stator plates as the rotor is operated. Shortcircuited tuning stubs 20, 2| are also connected to transmission lines Ill, H and provide means for controlling the reactance at the point of connection of the modulating means to the transmission lines when a condition of maximum impedance obtains at that point; It will b'e'seen that the movement of the rotor will cause the plates thereof to pass the two stator plates and alternately and progressively short-circuit the .two transmis-. sion' lines to ground at If! through these stator plates. v 'In the operation of the modulator 14, I5, Hi,

When, the rotor is in the position illustrated, with the one plate thereof entirely covering the stator plate 14, transmission linell will be short-circuited to ground at I9 and will not pass any current tothe load 2. Atthe same time currentwill flow from coil 5 through transmission line l0 directly to load 13, the modulator not drawing any current from line ID at this time. As the rotor I8 continues its movement, the one plate thereof will pass away from stator plate l4, thereby causing-an increasing amount of current to be drawn throughline'll tothe useful loadZ, while I plied to the useful load.

It will be seen that the radio frequency'energy output of the source will be supplied to the useful and passiveloads in. amounts which will vary .in accordance with the size and positioning of the stator and rotor plates and that the frequency of the supply of maximum or minimum current to either of the loadswill be determined by the speed of the rotor and the number of the rotor and stator plates. The two loads will therefore be supplied with current at the same radio frequency, modulated equally but with opposite sign,

whereby the total power supplied to the two loads willremain substantially constant.

A dummy load is associated with load 3 in the same manner as described hereinbefore with respect to dummy load 13 and useful load 2, and radio frequency energy is supplied' to' these two loads through transmission lines 3|, 32, respectively. Tuning stubs 33, 34 are connected to the transmission lines for a purpose which is identical with that of stubs 20, 2|. Modulating means comprising a rotary capacitor including the stator plates35, 36 and the rotor 31 are provided and are I operable, in the same manner as the means described hereinbefore, to vary the power supplied to the two loads 3 and 30 in such a manner that the power supplied to the passive load 30 at any instant will be equal to the difference between the maximum amount of power drawn by the useful load.3 and the instantaneous power drawn by the load3, whereby, the total power supplied to-thetwo loads remains constant. In order to modulate the energy'supplied touseful load 3 at a characteristic frequency different from the modulationfrequency of the energy supplied to load 2,-the rotor 31 may be constructed in the same manner as rotor l8 and driven at a-different speed, or, as illustratedin the drawing, it maybe provided with three .or

more plates and, accordingly, may be driven at 'the same'speed-as the rotorlB. i Y

It will 'be seen that, by theprovision of the dummy loads and by the energization of eachof these in such a manner that the powersupplied thereto always has the described relation to the power supplied to the associated useful load, the

total power drawn by each branch of-the system disclosed will be maintained-constant'andthe total power-drawn from-the source I will therefore be constant, whereby it is possible to utilize a greater fraction of the possible output of the source in the useful loads.--' I "While I have illustratedand described one embodirnent of my invention, it will be apparent to .those skilled in the art that further improve- 'ments and modificationsthereofmay be-made without departing in any way from the spirit or scope of the invention, for the limits of which .referencemust be had to the appended claims.

- Whatliclaim is: I l 1 1. 'An electrical system for supplying modulated radio frequency energy to a plurality of useful loads such as antennasrcomprising a source of energy, a plurality of useful loads,

transmission lines connecting each of said loads to the source, a non-useful load associated with eachuseful load, transmissionlines connecting each of said non-useful loads to the source, means associated witheach useful load and its.

associated non-useful load for modulating the energy supplied thereto and comprising means for alternately and progressivelyshort-circuiting to ground energy from the transmission lines connecting the useful and non-useful loads to the source, in such amounts that the energy supplied to any non-useful-load' at'any instant is approximately equal to the differencev between the maximumenergysupplied to the associated useful load and the instantaneous energy supplied thereto. w I a 2. An electrical system comprisinga-source of radio frequency energy, 'a' plurality of useful loads such as antennas connectedthereto, means for differently varying the amounts of energy supplied by said source.to said useful loads, a plurality of non-useful loads each of which is as sociated with one of said useful loads and is connected to the source, .means for varying the amount of energy supplied to each of said nonuseful loads, the means for varying the energy supplied to each useful load and to its associated non-useful load comprising spaced conducting members connected respectively to the connections between the source and the useful load and

Images