US 2434955 A
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1411.27, 1948. y s. B; PICKLES 2,434,955
` I lIVOLDULA'IING SYSTEM Filed Aug. 25, 1945 ATTaH/VLT Patented Jan.' 27, 194g I1 \l'1isinvention relates `to a modulating system and more particularly to`r a 'system "':l'esgn'e'dv for use in radio beacons. t Y
In many radio beacons suh ascoursefand loealizer -beaeonsvor equii-signa'lrlidenaths, i't is desired to transmitdilently"hactizdfsi nals on opposite sides 'ofthefbeacon 'guidg-lire in order toI guide ,the `aircraft along` a course "oi intoaglanding Y Ih such systems *it `has. been f generally common practice? to use mechanical modulators` or the l-ike'in the separat-lines-to produce tl-re, independently modulated carrier Signals for application to thebeacon antnras.
l 1t is `a principal objectof my invention' to-profuVide a modulating system which is particularly usefullfor obtaining:carrierfwavesmodulted with diiierent signals; so 1 theta the Kcarrier combined it'ztli each on these -signals'mayf apzearkat independentterrnirialsaV It i'sansti-ll further object off-my l-nveitir'f to nrovide a sim'ple monitoring circuit for use with the-beaconf-modulating; System which willv indicatetlhe degree of unbalance 1dirctlyfaft the transinittng end ofthe'bea'eon-o.l
In aordance with 'afeature ofy inifention, I `provide a- `systerng;inwhiolfl a carrier wave-is modulated with@J rst and second signalin an unbalancedmodulator which produces "an outiiut of carrier freguency and thev signalV sifdebanils.
At the saine-time, thesame .carrier frequency is modulated-with the two signa-1s in a balanc-d modulator, Tone of these; signals being: reversed in; "phase respectgtoi thegother imodulator. This produces noui-,put signalsi'debands. onlyS The outputs from these two modulators aret/hen v'combined with oneanother across a conjugate-net; 'Wo l; s o that invorleof the output 1eads-f:the network appears :arri =:r energy andesidebands offfone of the signa-lsandat; the other 'outputteriln'nfalus appears'carri-ierY frequency 'and the't-hr `f Vthe sidebandlV signals. Monitoringycan-.then be 'achieyed merely by coupling f a.'v `llter circuit t one of the outputterminalsandyconneeting an indicator irl- `the output ofthe n-t'erito show p'es'ene of unwanted signalsatthat termina-1:;
A'b'et't'er understanding of myinventionqand suona- `signal` 4sources which may 90 and V15() cycle sources. Any-f two;V differing `ffrequerioiesmaygbe used; as isf well understoodpfinthe art. A c Jfier source I2 is arranged to supplycarrier'siinulf taneousITy-vto; an unbalanced-modulator. |;3 and a. ualanced:niodulatorV M -Energy -fromsources jr' and i l fis; applied over'line |45 tounbalan ,odg u'lator i3 and overv line :I 6 to balanced modulator i4.=resnective1y. As shownrati 180118 0i the'sig: na, for' example; thatsfmm source IJ-. eil-Ie.- versed-finphase in-line l 6 with respet to the enf 'ergylsuppliedat-line L5 n thezoutput ofi; balanced; modulator 13j willfappeancarriel;I requency; arldv-sideband tompvnentssof the. Signe-.1S from'l 0 and 4 Il, 'the signe'l frequency Qompqrlen ydelingremoved inthe usual-mannen lathe out; but of-.m0dulator Mwillr apnearnly Seban components fiimssB-nfl. .sourses 1U. and @ad the @menait-from ls9`11r9-lkwil1 bari-.1i phase opposition tbth'e ,Corresponding sidebar@ atthe output ,of mom-later 11i,a the-.carnet fregueny being` balanced.v `olli?, a .r1d Vtige signal'frequeney Components being infllilnaltlbridge 30 carrier 3 and sideband energy are supplied over line 34 to central radiating units 35. Thus is provided an equi-signal radio beacon which may serve either as a localizer beacon at an aireld or as a course beacon for guiding an aircraft between given points.
Because of the combination of the energy from the two modulators through bridge 20 and since signals from both sources I and II are applied to each of the modulators, reduction of signal strength of one source with respect to the other will not cause a shifting of the beacon course. If one of the sources becomes weak with respect to the other, it will merely result in lack of com plete balancing out of the signals causing a broadening of the course but the course line will be maintained in the same position, Similarly, if either of the modulators becomes weakened with respect to the other, a broadening of the courses will result but no shifting thereof. This factor is particularly of Value in localizer beacon arrangements or in landing beacon arrangements where a slight shifting of the course line may bring the craft following such a line dangerously close to obstructions.
In order to assure proper balance of the energy supplied in the beacon, I provide a monitoring circuit which may include a coupling loop 21 coupled to line 2S. Loop 21 supplies energy to a ilter 28 which is tuned to pass only sideband components from source I I. The output of filter 28 is coupled to a meter 29. When the circuit is properly balanced, there will be no component -from source Il in line 26 and meter 29 will read zero. However, in the case of any unbalance, meter 29 will give an indication and the degree of departure of this indication from zero will indicate roughly the degree of unbalance. Balance may be restored by adjusting phase shifter I1 to bring the energy into proper phase agreement at the bridge input terminal and by adjusting the amplitude of energy in the output of either or both of the modulators I3 and I4.
If desired, a second monitoring unit coupled by loop 21A to line 25 and provided with a filter 28A serving to pass only the signal component from source I0 and a meter 29A may be provided. In general, however, a single meter will serve the purpose of monitoring the entire station.
While I have disclosed a preferred form of conjugate network arrangement in bridge 20, it is clear that any desired form of conjugate network may be substituted in its stead. It is only necessary that such network serve to combine the sideband components from the two modulations in the proper phase relationship. Furthermore, it is clear that the particular type of beacon shown in Fig. 1 need not be used, if desired, but the energy from leads 25 and 26 may be taken to any known form of beacon such as the crossed loop type of beacon, if desired.
In Fig. 2, I have shown an antenna arrangement which may be substituted for that of Fig. 1 when an equisignal glide path is desired. The antenna arrangement of this figure corresponds substantially to that disclosed in an application for Letters Patent to Andrew Alford, Serial No. 442,069, filed May 7, 1942, now Patent 2,373,090, issued April 16, 1945. According to this arrangement, energy from leads 25 and 23 is fed over lines 25A and 26A to vertically arranged horizontal loops 31 and 36. Loop 31 is arranged at a height above the earth to produce a plurality of lobes having a null aligned with the desired angle of glide path. Loop 36 is arranged at a lower height, for example, half the height of loop 31, so that it provides a radiation lobe overlapping the null produced from antenna 31. In this manner, an equi-signal glide path carrying differently characterized signals is provided for guiding the craft to a proper landing.
It is clear that many diiierent forms of beacon arrangements may be used with the modulating system of my invention without departing from the spirit thereof. Furthermore, other types of systems may be provided to furnish the original modulated waves applied to the conjugate network such as 2U. Moreover, any type of antenna desired may be substituted for the particular horizontal loop type illustrated in the drawings.
While I have described above the principles of my linvention in connection with specic apparatusand particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation onthe scope of my invention as set forth in the objects of my invention and the accompanying claims.
What is claimed is:
1. A system for providing a carrier modulated separately with two dilerent signals, comprising rst means for supplying carrier energy and a first and a second signal sideband, second means for supplying said first and second sidebands with one of said sidebands being phase reversed with respect to the sideband from said first means, a network having two conjugate input terminals, two conjugate output terminals and phase reversing means between one of said input and one of said output terminals, means for respectively applying energy from said first and second means to said input terminals, and output means coupled to said output terminals for deriving said carrier energy and one of said sideband signals, respectively, from said output terminals.
2. A system according to claim 1 further comprising monitoring means coupled to one of said output means, comprising a lter tuned to pass the signal sideband dilering from that Wanted at the output terminal, and indicator means in the output of said filter.
3. A method of providing a carrier modulated separated with two different signals, comprising producing a rst wave combination consisting essentially of carrier energy and rst and second signal sidebands, producing a second wave combination consisting essentially of said first and second sidebands with said first sidebands reversed in phase with respect to the corresponding sideband rst named, combining said first and second wave combinations in phase coincidence to provide a first resultant wave combination of said carrier and said second sideband, and combining said first and second wave combinations in phase opposition to provide a second resultant wave combination of said carrier and said first sideband.
4. A method according to claim 3 further comprising the step of measuring the unwanted sideband component in one of said resultant wave combinations to determine unbalance between said first and second wave combinations.
5. A beacon modulating system comprising a first signal source, a second signal source, a carrier frequency source, a balanced modulator, an unbalanced modulator, means for supplyingy carrier to both said modulators, means for coupling said first and second sources to one of said modu, lators, means for coupling said first and second sources to the other of said modulators with the signals from one of said sources in phase opposition to the corresponding signals supplied to said one of said modulators whereby carrier and sideband energy of both said signals appears at the output of said unbalanced modulator, and sidebands only at the output of said balanced modulator, a four terminal bridge networkhaving a transposition in one arm thereof, means for applying the outputs of said modulators, respectively, to diagonally opposite terminals of said bridge network whereby carrier energy and said first signal sidebands appears at one of the remaining terminals of said bridge, and carrier and said second signal sideband appears at the other terminal of said bridge.
6. A system according to claim 5 further comprising phase shifting means in the output of one of said modulators for shifting the phase of said bridge.
7. A system according to claim 5 further comprising output lines coupled to each of said remaining terminals of said bridge, and a monitoring circuit coupled to at least one terminal of said bridge, said monitoring circuit comprising a lter tuned to the frequency of the sideband of the signal not wanted at said one terminal and an indicating meter coupled to the output of said lter.
SIDNEY B. PICKLES.
REFERENCES CITED The following references are of record in the ille of this patent:
UNITED STATES PATENTS Name Date Pickles Nov. 17, 1942 Klopsteg JulylS, 1933 Alford Feb. 9, 1943 Number