US2946998A - Direction finder - Google Patents

Description

July 26, 1960 s. A. w. JoLLlr-'FE ErAL 2,946,998

DIRECTION FINDER Filed March 21, 1958 2 sheets-sneer 1 j 6 5 l T z 4 c 1, 3 umu i a 2 f f l I L l l s@ mma@ ML Maa/fel ULL/m am Z371 if UM AT-rRNEYs July 26, 1960 Filed March 2l, 1958 s. A. w. JoLLlFFE ET AL 2,946,998

DIRECTION FINDER 2 Sheets-Sheet 2 ff f2 F/G. 4.

" Patented July26,

2,946,998 nmncrroN arianna Sidney Arthur Walter '.lolliiie, Maldoxnand David Wiliiam Watson, Great Baddow, England, assignrs't'o .mean amplitude. `In otherwords, the @veran requins change, peak to crest, maybe expressed by 'a ratio of 9:1 for, in Fig. 1, if the dimension a='l, b=9Y Iand the Marconis Wireless TelegraplrCompany LimitedyLondon, Eng'iand, a company of Great Britain nnen Mar. zi, 195s, ser. No. 722,941 f Claims priority, application Great Britain Apr. 26, 1957 's 'claim (cl. 34a- 11st i forms, ya usual form being that in which a fixed Vaerial system feeds into the stator of a radio goniometer whose rotor is continuously rotated, incoming; signal direction being ascertained by comparing the phase of a signal derived from the rotor output with the phase of a signal derived from a reference frequency generator providing afrequency equal to that of rotation of directivity.

The invention is illustrated in and explained'inconnec- Y tion with the accompanying drawings. In. the drawings of this kind are, of course,V Well'known and take many Figs. 1 and 3 are explanatory graphical figures; Figf?.

is a diagram of `an embodiment of this invention;V and Figi. 4 shows a modification of 'the arrangement of Fig. 2. Y

A diiculty which arises in a; -direction finder ofthe be r'eaiglylavailable.

kind referred to is that the continuous rotation Vof directivity superimposes a modulation of the. rotation frequency on the received signals and if thosey vsignals include speech or other intelligence which is to be separated out and reproduced, the superimposed modulation due to the rotation of directivity may spoil the speechor other intelligence or even' make it completely unintelligible, for the frequency ofthe modulation due torotationl ofY directivity isa low frequency, 25 c./s; being a common gure. l Y y The difficulty abovementioned cannot besatisface torily avoided-as would at first sight appear to be the case-by merely superimposing a counterbalancing locally generated. frequency equal to that dueto directivity rotation on the intelligence signals.' The' reason for this may b`e:explained with reference-.to Fig.' l. Witha'practical direction iinder of the kind referred to, sensitivity is dependent on the depth of modulation of the incoming radio frequency carrier and in practice Vthis depth can sometimes be as much as 80%. Thus in order to make speech or other intelligence signals derived from the goniometer rotor satisfactorily intelligible, one has to demodulate a post-detector speech band Which may l b -g b-l-a which is the case for 80% modulation-fthe amplitude at the trough Will have to be increased in a ratio of 5:1 and the amplitude at the crest will have to be decreased in a ratio of 1.8:1 if both are to be changed to the Demodulation of this wave may be deemed totV mean amplitude c'='5. It will now be seen, therefore,

Vthat merely superimposingfa counterbalancing locally generated sine wave on the lreceived signal VWavewill not get'rid ofthe directivity rotation modulation of the :intelligence signals. The present invention seeks togetrid of this modulation or` to* reduce it to 1an acceptable amount. In its broadest aspect, the invention consists'in vsubjecting a Vsinusoidal Wave of'dire'ctivity-rotation frequency to gain control in' dependeneeupon the momentary amplitude of that wave and utilizing 'the gaincontrolled Wave atleast partly to counterbalance an undesired cornponentof the same frequency in the directionallyreceived signals; K Y Y According to a featureof this in ention a radio directio finder of continuously rotated directivity and including -a channel for recovering intelligence signals modulating. incoming Waves' Whose `direction is to be Y'ascertainedeomprisefs means for deriving a low frequency Wave of the frequency of rotation of directivity, an amplifier Vconnectedtofainplify said wave and having gain which is a function of and increases with increase of input'ain'p'litu'ddl and means fo'r superimposing theout- -fp'ut of said Yarjn'p'lilier upon'vthe vsignals in saidfehannn in Yphas'eoppo'sitio'n to the component of directivity-rotation frequency which 'will be present in said signals so as to Vaiinul or substantially reduce said component.

It i`s possible to constitute the amplifier bfya simple variable ,u valve amplifier but, in practice, variable `-,u valves of siiicientcurvature of characteristic may not It may therefore be preferred to include a nnelinea stage in said channel at a point'subsequent to that at which the output of said* amplifier is superimposed, said stage operating over a substantially straight part of its characteristic as respects therintelli- Y gence signals and thephase' ofthe superimposed signalsv b'eii'igrso chosen that the curvature characteristio'of the non-linear stagek supplements that of the vampliiier ani- 'plifying'saidflow frequency wave. g.

Preferably said Vwave is derived by altering it out from tnesignanfed iii to said manner VPreferz'ibly' alsorneans are provided for adjusting` thel phase va'nd'-ar'nplitude of the derivedlwave and, advan-V 't`ag '5t`1s`ly,` -a-fcathode ray 'tubemo'nitof fed with lsignals taleii fromfsaid channelV at 'a point subsequent .to-thati at up'erii`nposition of saidl output takesy place is pro` 'vided ffac'litte Yadjlltlilent. Y

Fig. Zris a bloclc diagram of one embodiment of the Referring to Fig.. 2, reference character 1 Yrepresents a fixed direction-al aerial system of any kind known per se and which supplies signals to a known continuously roe tated goniometer represented by the block 2. VThe rotor of the goniometer is rotated ata desired speed, for ex`` Vrotation of its rotor, e.g. 25 Vc./s.

Output from theV goniometer rotor ispassed to aV radio frequency amplifier and frequency changer 5 .followed by the usual intermediatepfrequency amplifier and detec-VV tor 6. The VradioV Afrequency .amplifier and frequency changer are both represented by the bloclcS and the intermediate frequency amplifier and `detector are both represented by the block 6. Detected output fromthe unit 6 is amplified and passed through a low pass filter at 7, the low pass filter being adapted to pass the frequency of rotation of directivity-in the present case 25 c./s. The output from the unit 7y is fed to` an anu 'Y 3 plitude limiter 8, further amplied by an amplier 9 including another similar low pass filter, and supplied as one input to a known phase discriminator unit 10.

Output from the generator 4 is passed through low pass filters 11 land 12 similar toV the filters at A7 and 9, and thence fed as the second input to the phase discriminator 10. As is well known the phase relationbetween the two inputs to the discriminator willbe a measure of the direction of the incoming signals andthe discriminator may operate a known bearing indicator 13 which may be calibrated directly in bearings. The' apparatus as so far described is all well known and in accordance with common practice and needs no further description here. v

Output from the unit 6-which will consistof intelligence signals, e.g. speech, modulated at the 4frequency of directivity rotation is fed to a speech amplifier 14 shown schematically as a two-stage amplifier. Output is also taken from the 25 c./s. lter at 7 through an adjustable phase shifter 15 to the control grid of a non-linear valve amplifier which may conveniently be a Variable y. pentode 16. This valve is operated as conventionally shown by the graphs in the accompanying Fig. 3 which require no description beyond stating that Vg represents grid voltage and gm represents gain. The output of the valve 16 is fed through an `amplitude adjusting device 17 of any known kind, eg. a potentiometer, and superimposed on the signals from the unit 6fat the input of the speech amplifier 14 shown as a two stage amplifier comprising two triodes of which the rst is the demodulator. Output from the speech amplifier 14 is taken to a loudspeaker or telephones 18 and is also taken to a cathode ray tube monitor 19. As will be seen by suitably choosing and adjusting the operating parameters of the valve 16 and suitably adjusting the phase and amplitude controls 15 and 17, the 25 c./s. input fed to the control grid of the first valve in the ampliier 14 from the valve 16 may be caused to be, to a suciently close degree of approximation, in phase opposition with and such as to cancel out the 25 c./s. component (due to goniometer rotor rotation) present in the input fed to that control grid directly from the unit 6.

In use the phase and amplitude controls '15 and 17 are adjusted until the 25 c./s. modulated wave (shown as an envelope wave in full lines on the representation of the tube at 19) are transformed into the partially broken straight lines (also shown in that representation) corresponding to the desired result, or as nearly to those straight lines -as can be achieved. Ideally, by adjusting the controls 15 and 17 complete cancellation `of the nterfering component is possible. Although in practice the idea is not to be expected, a practically sufficient approximation to complete cancellation is readily obtained.

It may not always be conveniently practicable to oba tain a variable ,u valve 16 of sucient `curvature of characteristic and for this reason the modiied circuit of Fig. 4 may be preferred. `Like references denote like parts in Figs. 2 and 4. In Fig. 4 the demodulator valvehere referenced 14a also has a non-linear characteristic of the nature of that'of the valve 16. Its control grid is fed from the junction point of the units 6 and 7 as is the demodulator valve (the tirst valve of the speech amplier 14) in Fig. 2 but a phase inverting valve 20 is interposed between the amplitude adjuster 17 and the said control grid ofvalve 14a. The audio frequency level at the junction point of the units 6 and 7 is arranged to be low enough toV sweep over only a substantially linear part of the characteristic of the valve 14a the gain of which is however, varied by the directivity-rotation modulation frequency,` theV inverting valve 20 being inserted to procure the result that the effect of the curvature of characteristic of valve 14a supplements that of the curvature of the characteristic of valve 16to produce an overall curvature of-characteristic which is suicient even though that of the valve 16, alone, is not.

We claim: Y

l. A radio direction finder of continuously rotated directivity and including a channel for recovering intelligence signals modulating incoming waves whose direction is to be ascertained said direction nder including means for deriving a low frequency wave of the frequency of rotation of directivity, a non-linear ampliiier connected to amplify said wave and having gain which is a function of and increases with increase of input amplitude, means to adjust the phase and amplitude of said amplitier andV means for superimposing the output of said amplifier upon the signals in said channel in phase opposition to the component of directivity-rotation frequency which will be present in said signals so as to annul or substantially reduce said component.

2. A direction iinder as claimed in claim l wherein a non-linear stage is included in said channel at a point subsequent to that at which the output of said non-linear amplifier is superimposed, said stage operatingl over a substantially straight part of its characteristic as respects the intelligence signals and the phase of the superimposed signals' being so chosen that the curvature characteristic of the non-linear stage supplements that of the non-linear amplifier amplifying said 10W frequency wave.

3. A direction finder asV claimed in claim l wherein there is provided a cathode ray tube monitor fed with signals taken from said vchannel at a point subsequent to that at which superimposition rof said output of said amplifier upon the signals in4 said channelris effected.

vReferences Cited in the le of this patent UNITED STATES PATENTS 2,839,750 Kaltenbacher v Iune 17, 1958

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