US2439656A - Receiver protective device - Google Patents

Description

April 13, 1948. w. HAUSZ 2,439,656

I RECEIVER PROTECTIVE DEVICE Filed Aug. 17, 1942 7 RA/VSM/ 7' TING l3 APPJHATUS AFPAHAWS Inventor: Walter" Hausz,

. is Attorney.

Patented Apr. 13, 1948 RECEIVER PROTECTIVE DEVICE Walter Hausz, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application August 17, 1942, Serial No. 455,050

7 Claims.

My invention relates to high frequency transmission systems and it has for one of its objects to provide improved means to protect the re ceiver of such systems from high voltages to which the line, over which the received oscillations are transmitted, may be subjected.

My invention relates more particularly to transmission systems in which both a transmitter and receiver are connected to a common line which may lead, for example, to an antenna by which desired oscillations are radiated and received, and it has for one of its objects to provide an improved means to protect such a receiver from the intense oscillations produced by the associated transmitter.

Another object of my invention is to provide such means particularly adapted for use at short wave lengths.

In such apparatus operating at short wave lengths, and particularly that class of apparatus in which the oscillations produced by the transmitter occur in short pulses which are radiated and then again received after reflection from a remote reflecting surface, one means for protecting the receiver comprises a non-linear impedance device connected across the end of a stub transmission line of such length and so connected to the line as to produce low impedance across it during operation of the transmitter and high impedance during reception of the received echo.

One of the objects of my invention is to eflect certain improvements in the operation of such apparatus and in particular to improve the protection afforded the receiver by such apparatus.

Another object of my invention is to provide such an arrangement of the apparatus that certain undesired efiects during reception, produced upon the line by the impedance of the transmit ter, are avoided.

The features of my invention which I believe to be novel are set forth with particularity in the appended claims. My invention, itself, however, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 shows diagrammatically the equivalent electrical circuit of my protective device and Fig. 2 shows a physical embodiment of the device.

Referring to the drawing, I have shown in Fig. 1 transmitting apparatus I and receiving apparatus 2 connected by means of branch transmission lines 3 and 4 respectively to a main transmission line 5. Transmission line 5, in turn, may

be connected to a single directive antenna, not shown. The transmitter l, at predetermined intervals, supplies a pulse of high intensity over the main transmission line 5 to the antenna, then is inoperative while this signal travels through space to a reflecting object and returns to the system to be picked up by the antenna and detected in the receiving apparatus 2. .As will be readily understood the reflected signal is much weaker than that supplied by the transmitting apparatus and the receiving apparatus must be adapted to detect this weaker signal. Since both the transmitting and the receiving apparatus are connected to the transmission line 5, the receiving apparatus may be adversely affected by the strong signal of the transmitter unless means is provided for preventing the transmitted signal from reaching the receiving apparatus over transmission lines 5 and 4'. during the transmitting period. Also, during reception, the transmitter l and the branch line 3, by causing reflections of the signal at the junction of lines 5 and 3, may adversely affect transmission of the relatively weak returning signal over the line 5 to the receiver unless the transmitter and the connecting line 3 are electrically isolated from the system during the receiving period.

In accordance with my invention the junctions of branch lines 3 and 4 with main line 5 are spaced apart by a distance equal to an odd multiple of an electrical quarter wave length of the radiated oscillations of the pulses produced by the transmitter I. In using the term odd mul tiple, I mean to include the multiple one. The junction points of branch lines 3 and t with main line 5 have been designated respectively as points 6 and 1. Because of the spacing of these junctions, a short circuit across line 5 at point 1, by reason of the impedance inversion effect of the line, well known in transmission-line theory, appears as a very high impedance across the line at point 6.

As one means for short-circuiting transmission line 5 at point 1 during a transmitting period, I provide a stub transmission line 8 connected to the main line 5 at the junction point 1 by means of a short coupling line 9. Stub line 8, comprising an outer conductor it and an inner centrally disposed conductor H, is short-circuited at its lower end at the point l2 and is terminated at its remote end by means of a non-linear impedance device l3. For a purpose to be pointed out later, coupling line 9 is connected to the inner and outer conductors of stub line 8 at a point close to the short-circuiting point l2. De-

The electrical length of the stub line 8 between" the short-circuit point I 2 and the terminating gap i3 is made equal to an odd multiple of a quarter wave length of the'output wave of-the transmitter. For a wave of this'fre'q-uency, line 8 is a resonant line short-circuited at one end and terminated in a non-linear impedance-at the 01 posite end.

At the low voltages present in the system-when the antenna is receiving: signals and supplying them over line- 5 to the receiving apparatusz, the

tuned line fl presen'ts a very high impedance to the short couplingiline 9 andconsequentlyihas very little efiect on signals transmitted on line 5;

When the transmitter! is sending out 'a' signal pulse of high intensity; however, voltages of an intensity'sufilcicnt to break down'the-spar-k ga v l3 arebuilt up on lines 5 and S, conduction of current between the electrodes of the gap resulting in the'detuning of stub line 8.- Under-thiscondition, since the coupling line 9 is joined to the stub line 8 at a pointclose' to the short-circuiting connection (2, the "stub'line presents but a small net inductive reactance across the main line 5.

In order to reduce still further the value of the' impedance presented across line 5, variable capacitor I6 is connected between-the inner conductors of main line 5 and stub'line 8 -and isadjusted to series resonate with the-small in-- ductive reactan'ce of the stub line; As aresult the combination of the stub' line, the short coupling line, and thecapacitor M appears as -a substantial short-circuit across main transmission line 5 at the point of its junction with line' i connecting it to the receivingapparatus; By careful adjustment of the capacitor M to the point of exact resonance with the stub line, the

value of the resistance presented across the main transmission line at this junctionpoint may be reduced to a value less than one ohrnso that the receiving apparatus is effectively short-circuited from the high-intensity signal developedby the transmitting'apparatus. Since, as previously stated, the length'of the'main line between the points of connection with the branch lines 3 and 4 is an odd multiple of a quarter wave length of the output wave of the transmitter, the short circuit across the main lineat thepoint I is inverted by the transmission line 5 to appearias the high impedance at the junction point 61' Hence, while the series-resonant circuit comprising. stub line 8 and capacitor is effectively preventsthe transmitter output from reaching 'the receiving apparatus, this circuit has no effect on'the transmitting apparatus itself.

When the gap i3 is non-conductive and the" receiving apparatus 2 is adjusted for 'the reception 'oisignals, it may be found that the branch line 3 and-the transmitting apparatus present such animpedance to the-main line '5at the 'poirit" '6 that reflections occur: lf th'e impedance presented by the branch *line 3*to the emain line'at the point t is quite high, theeffect of this line on the receiving .circuit"is negligible; but if .the'impedance is low; it may cause'refiections-on the main line and tend to attenuate the received signal. Variable coupling capacitor !5, in series with the inner conductor of the line "a, and variable coupling capacitor it connected across the stub line 8 are provided to compensate for such a low impedance at junction 6 in a manner now to be described.

If there is a low net capacitivesusceptance at the junction point 6,- capacitor it: may be adjusted so that the branch line 4 presents a low capacitive reactance plus the receiver resistance to the man line i 5 --at the point i. The portion of line 5 which'lies between points 6 and 'i, being an odd multiple of'a' quarter-wave length of the output wavein length; acts to invert the low capacitive reactance presented by the line in both phase and magnitude, thus giving a low net inductive susceptance in parallel with the conductance of the receiver at the junction point 6. The value of this inductive susceptance may be adjusted by means ofcapacitor IE" to cancel the capacitive susceptance presented by line 5, leaving only the receiver conductance, previously matched to that of the line 5.

If, on'the other hand; there is-a low net-inductive susceptance presented by line 3 at thejunction point E5, capacitor lfimaybe adjusted to detune the-resonance of stub line 3 so that the net-reactance-at'the junction point 1, including the stub line in parallel with capacitor l5 and Theportion of line 5 between points 6 and I again the receiver2; is'a low inductive reactance.

acts to invert this reactance in both phase and magnitude so that it is effective to-producea lowcapacitive susceptance at the junction point 6. The'value of the capacitive susceptance may be adjusted bymeans of capacitor l6 toresonate with the low inductive susceptance of transmission 1lne'3, again leaving only the receiver conductanceat thepoint 6.

Has a result of the-adjustments outlined'in the two preceding paragraphs, the conductance of thereceiver, as it appears at the junction point 6, does not match the characteristic conductance ofline '5 i at this point, further adjustments ofboth capacitors l5 and it maybe made to match exactly the impedance ofline 2- with that of line I, thereby completely eliminating-reflection.

'Ih-esystenr thus'described provides a' protective device for signallingapparatus, employing both receiving and transmitting equipment connected by means of a single tran-smission .line to an antenna, which both substantially shortcircuits the receiving apparatus during the transmitting period and removes the effect of the transmitting apparatus from" the receiving apparatus during the receiving period. The

resonant line iishortedat one :endandterminated in a non-linearimpedance device-at the other end, acts as a parallel resonant circuitpresenting a-very high impedance across the input when connected" to themain transmission line-through the coupling capacitor It. This resonant line has very. little effect inthe presence of'low vol ages. When the transmitter is sending out short pulses, voltages suficient to change the characteristic of the non-linear impedance device occur, thus detunin'gthe resonant line so that" it effectively; presents only: the very small in-- ductive impedance of a short stub on its -lower section. Bymeansof the-variable capacitor Hi, this inductive" impedance is series tuned to present an efiective'short circuit across': the main transmissionline." By: proper spacing 0f the junctions :of lines -3 and4 *withrr'espect-toline 5;

the low impedance which exists across line 4 at junction point 1 is inverted to appear as the high impedance at junction point 6 so that not only is the receiving apparatus protected from intense signals of the transmitter, but also the presence of the receivin apparatus does not aifect the operation of the transmitter. Furthermore, by means of variable capacitors I5 and I6, adjusted in the manner previously described, the impedance of line 3 and transmitting apparatus I is matched with the impedance of line 5 at the point 6 so that this branch of the system does not cause reflection on the main line 5 during the receiving period.

In Fig. 2 I have shown in greater detail one physical embodiment of the protective system diagrammatically illustrated in Fig. 1. Preferably, the transmission lines 3-5 comprise an outer conducting tube 20 and an inner centrally disposed conductor 2|. Suitable insulators 22 are used to retain the conductor 2| centrally disposed with respect to tube 23. The outer tubes and inner conductors of the branch lines may be joined to the outer tube and inner conductor of the main line in any suitable manner, as by soldering, brazing, or the like. The short coupling line 9 may comprise an outer conductor, such as the metal housing 23 soldered 01 brazed to tubes l and 20 of lines 4, and 8 and inner conductors 24 suitably secured to inner conductors II and 2| respectively. Connected in series with conductors 24 and located within the member 23, is the multiplate variable capacitor |4 comprising fixed plates 25 and rotatable plates 26. The position of plates 25 with respect to plates 25 may be adjusted in the usual manner by a control knob, not shown.

The inner conductor H of the stub line 8 is divided into upper and lower sections, both of which are attached to a metallic cylinder 21, which forms the fixed plate of the variable capacitor IS. The movable plate of capacitor l6 comprises a metal plug member 28 electrically connected, as by means of a flexible cable 29, to the outer tube ll] of stub line 8. The capacitance of capacitor l5, determined by the position of member 28 with respect to member 21, may be adjusted in any suitable manner, such as by means of a rack 30 attached to member 28, pinion 3|, and operating handle 32. The plates 21 and 28 are separated by means of an insulating cylinder 33 comprising, preferably, va synthetic material of the polystyrene type having a good power factor.

As previously stated, for purposes of illustration, the non-linear impedance device l3 has been shown as a spark gap and may comprise an electrode 34, having a screw threaded projection 35 from the bottom thereof which may be attached to the end of the inner conductor ll of the transmission line 8 in a manner to be described later, and. an associated electrode 35 which may be mounted upon a conducting plate 31 closing the end of the transmission line 8 and being joined thereto, as by brazing or the like. The space between the electrodes is enclosed by means of a glass cylinder 38 hermetically sealed to the electrode 34 and the conducting plate 31, The electrodes are of solid conducting material and are surrounded within the glass cylinder 38 by a low pressure atmosphere of a gas having a very fast deionization time, such as hydrogen or helium.

In order to provide for ease of assembly of the stub transmission line, as well as to reduce the strain on the glass cylinder 38 during expansion and contraction of the metal of the stub line, conductor H is provided with a movable section comprising an inner member 39 attached to the metal cylinder 21 and a sleeve member '39 in threaded engagement with the screw threaded projection 35 and having a plurality of springlike fingers engaging section 39 of conductor for assuring good electrical contact therewith.

Variable capacitor |5 may comprise a fixed plate 40 and a movable plate 4|, the fixed plate 4!] being connected to conductor 2| in any suitable manner. As shown a screw 42 has one end in threaded engagement with plate 4|! and the other end secured to conductor 2|, as by brazing or soldering. A disk 43 of suitable insulating material, clamped to plate 49 by means of clamping nut 44, maintains plate 40 centrally disposed with respect to tube 2|]. Movable plate 4| is preferably joined to a movable conductor 45 having a threaded portion 46 and an adjusting knob 41. A tubular conducting member 48, suitably connected to the portion of conductor 2| extending to the receiving apparatus and supported in spaced relation with tube 23 of line 4 by means of insulating disk 49, surrounds conductor 45 and has a slotted portion comprising a plurality of fingers 5!] of spring-like material for making gOOd electrical contact with conductor 45. A nut 5|, engaging threads on the outer surface of member 48, is used in conjunction with a retaining ring 52 suitably attached to member 48 to clamp the member 48 to the insulating disk 49, thus fixing the position of member 49 with respect to tube 28. The spacing disk 53 secured within member 48 is internally threaded for engagement with threaded portion 46 of conductor 45. By means of knob 41 and threads 46 and 53, the spacing of variable plate 4| with respect to fixed plate 40 may be adjusted to vary the capacity of condenser I5 for the purposes previously explained.

While I have shown a particular embodiment of my invention, it will of course be understood that I do not wish to be limited thereto since various modifications may be made, and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a transmission line, apparatus connected thereto and operating with respect to oscillations transmitted over said line said line being subjected to high voltages of a certain frequency, mean to protect said apparatus from said high voltages, said means com prising a stub line having a length equal to a quarter of a wave length, or odd multiple thereof, of oscillations having the frequency of said high voltages, said stub line being short-circuited at one end and having points spaced from said short circuit connected to opposite sides of said transmission line through a capacitance, and an impedance across the opposite end of said stub line having high value to low voltages and low value to said high voltages, said capacitance having such a value as to resonate with the inductance presented by said stub line when said impedance is low, whereby said stub line and capacitance produce a short circuit across said transmission line during high voltages thereon and high impedance across said line in the absence of said high voltages.

2. In combination, a transmission line, apparatusconnected thereto and' -operati'ng with re sp'ect to oscillations transmitted over said' 1ine," said 'Ii'nabeing subiected to high voltages of -"m certain frequency; means "-to protect --said 1: apparatusfr'om said high voltages, said means' com prising a stub line'having a'lngthequaitd a qnartei of a wave length, or oddmultipiethere of, of "oscillations having the fre'quency 'of said high voltages, said-stub line 'being'-short-circuited atone endand having an i np connected mitting apparatus and said antenna-and between a.

said antenna and said 'receivingapparatus; the points of connection of "saidapparatuses with 'said line being spaced apart by a distance equai to an odd multipleof-a; quarter wave length ofsaid osciilations,= mean-s"for interrupting transmissionofsaid oscillations to said receiving apparatus when'fsaid-transmitting apparatusis operating to produce osciilationsaof high intensity; said means comprising a stub transmission line; a nondi-near impedance element 'Iconnectedacross: one :end of. said stubline; said element havingazlow im pedance value to said oscillations of h-igh inte'n sity and: a high valueto-osciliations received from' said antenna; and reactance means connected be tween said? stubi line 1 and: said? first I line at the point of connectionl'with saidcreceivingapparatus: for tuning said stub line to series reso-nance at the frequency of saido'sciiiation's whenasaid transmitting apparatus is operating, said stub dine-Sand said reactance means being eff'ectivewwhen reso nating ltoproducer an 10w impedanceafacross said i first iinepat saidpointof connection;

4; In: combination; a transmissionirline; res ceiving apparatus connected thereto'to TECEiVBTOS cill'ationsover said-line: .a transmitter: connected to said line tosupply oscillations th'ereovergrandi an impedance meansconnected acrosszs'aidt'line at apoint between said. transmitter "and'receiver," the impedance oi -'said-imeansbeingiilow during;-

the high voltages product-vetby saidrtransmitt'en and high during the-absencaofi said'highzvoltagesp said transmitter presenting reactive": impedance to said'line-producing undesired reflectionsdure" ing reception, .saidimpedance-means during :;re.+-

ception" presentingclike reactancerto :saiddine at i said point, the distance between said 1- point and v the point of connection of said transmitterbein-gz such that-said reactances appear inmoppositer' sense at the point -:ofconnection: ofisaid" trans:

mitter; and theimpedance ofsaid impedance means being of such value that reson'ance occurs at said pointof connection-of saidtransmitter.--

5. In a. combination,- a transmission line; receiv ing: apparatus connected thereto to receive oscii lations-over said 1in.e, a transmitter-connected-itoz saide-ilineto supply: oscillationsthereover; said:

transmitterpresenting-reactive impedance to-s aid line-producing undesirablereflections during-re ception; impedance means" connected between sa'd apparatus and said line; said" impedance nieans diiring reception-presenting flike- 'reactance to saidiine, the distance betwe'en s'aidimpedance means and "the-point of connection of said transmitteribein'gsuch thatsaid "reactance's appear in opposite sense at the point or connection of 'said' transmitter, and theimpedance of said" im-- pedance means -being-of such=va1uethat resonance occurs at said point of connection' of said: transmitter.

6. In combination, a receiver, atransmission iine-extending-th'ereto over which oscillations are received, a transmitter connected" thereto at a= point distant from said= receiver "presenting un'--' desired 'react'ance'to said line; and means-to pro-- tect said-receiver from voltages produced by said 20 transmitter andto avoid reflections -produced=-bysaidreactance, said means'comprisinga stub line'- conrrected across said transmission line at a-point between'said transmitter and'receiver and pre sentinghigh impedance thereto between periods of operation of said transmitter; means-to reducesaidimpedancetoa 1ow=inductive value-in re sponse to oscillations produced bysaid'transmitter; means connected to said stubiine-to reso= nate-withsaid iow' inductive impedance atsaid point andto render said high impedance reactive and ofiike'sign to the impedance-of'said transmitter, said point'being so'spacedfromthe connectiorr between said transmission iine'and trans: mitter that said transmitter-reactance and said -'.high" impedance appear" of unlike signs" at the" point of connection of said transmitter."

'7. In combination, a receiverya" transmission line extending thereto over which oscii'lations are received; a transmitter connected thereto 'at a point distant from said receiver presenting-"undesiredreactance to said line; and meansto pro-'- tect said receiver from'voltages produced by said transmitter and to avoid reflections produced by said-reactan'ce;- said means comprising a' stub line connected across said transmission line at 'a point-"between'saidtransmitter and receiver and presenting high impedance thereto between periods of operation-10f said transmitter, means toreduce sa-id impedance to a low inductive valueintesponse-to oscillations produced-by said transrnitt'er means-connectedto said stiib iirie to 'resonate said'ilowinductive impedance at-said. point; and reactance means-connected between said receiver and said point, said reactancemeans beingeffective touprovide a--reactanoe at said point of like sigh to saidundesired reactance; said point being so spaced from the connection between 1. said: :transmi'ssion'i line land: said transemitterz: that a resonance occurs between said 'reactance andfisaid undesired reactance at I said connection-of said transmitter."

' WALTER HAUSZ.

REFERENCES" CITED The following references 1 are "of F recordin thefii'e' of- 'thispatent UNITED STATES PATENTSL Number Name Date r 2,189,549 Hershberger.: Febsfi; 1940.. 2,202,!Z00'? Leeds May 28;i 1940=

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