US2973491A - Attenuator - Google Patents

Description

Feb- 28, 1961 A. H. MAclszEwsKl ETAL 2,973,491

ATTENUATOR original Filed May 1s, 1954 United States Patent O sig'nors to A.R.F. Products,.1lnc., -River Forest, Ill., a corporation of Illinois Griginal V:application May 13, 1954,/Ser. No. 429,547,

Ynow Patentl No. 2,881,315, dated Apr. 7, 1959. Di-

vided and this application Apr. 21, 1958, Ser. No.

Claims. (Cl 333-81) This invention relates to an attenuator and particularly to an attenuator of the wave-guide type.

It is an important objectof the present invention to provide an improved radio frequencyl output attenuator of. the wave guide type.

Yet another object of the invention is to prov-ide an improved radio lfrequency output attenuator which vis responsive only to the voltage induced by the inductive coupling mode and in which the coupling can be adjusted.

-In connection with the 'foregoing object it is -a still further object to provide an attenuator in which there is practically -no mistuning of the principal radio frequency tank vcircuit due to the degreeof coupling theretoV by the attenua-tor.

Y Figure 1 -is a view in vertical section through` a. -radio frequency `output attenuator made in accordance with and embodying the principles of the present invention;

Figure 2 is a view partially in cross section of the attenuator of Figure 1 substantially as seen in the direction ofthe arrows along the line 2-2 of Figure l;

Figure 3 is a view `in vertical cross section ofthe atenuator of Figures l and 2 substantially as. seenin the direction ofthe narrows along the line 3:-3 of Figure 2;

Figure 4 is an end view of the lattenuator of Figure 1 as viewed -frorn the left hand end in Figure -1 jvFigure 5v is Ian enlarged partial view in cross section substantially as seen inthe ydirection of the arrows along the line 5--5 of Figure 4 and illustrating theconstructiop of the capacitive mode suppressor; and

Figure 6 is a schematic electrical diagram of the attenuator of Figures 1 to 5 and showing `the'relation thereofV to associated circuit components. AReferring now particularly to Figures 1 and `6 of the drawing, Vthere is shown an output radio frequency attenuator made yin accordance with the lembodyi'ng'the principles of the present invention, the attenuator beingkgenerally designated by the ynumeral 191. The attenuator includes in general apick-up coil 192, one vend of which is ygrounded as at 194 and the other end 196 of which is connected to the electronic equipment to be tested. Coil 192 is inductively coupled to an associated coil such as a coil 134 in a tank circuit. An electrostatic shield 198 is provided to prevent excitation of the pickupY loopY or coil 192 by capacity coupling. The pick-up coilf192is`positioned within a metal tube 200'so that the tube and coil operate on the inductive-coupling mode as a wave guide below cuto.

A pick-up loop or monitor wire 202 vis provided, the monitor wire extending into the tube 200 and being positioned between the pick-up loop 192 and the electrostatic shield 198. The position of the monitor loop 202 is adinstable.w A connection is made from the monitor Ioop 2,02 through a rectifier 204, a resistance 206 a Airst invductance 208 and a second inductance '21.0 to a speaker. `A capacitor 212 by-passes rthe resistance 206 to ground.

'l g rThe wave guidebtube 200 is preferably circular in cross section Vand is open at both ends, one end being provided g 2,973,491y Patented Feb. 2s, 1196i with an outturned attachrent lia-nge 214 which Lis to attach the attenuator lto the @chassis of the signa-l generator. Theother end of tube 200 has a plurality lof slots formed therein which receive three at pieces or straps of metal 216 which form the electrostatic shield 198. From lFig. 4 it will be seen that the straps 216 are disposed parallel with each other with the center strap lying along a diameterof tube 200. y*It will be further seen that thejorientation of the straps 216 is `in a plane perpendicular to the longitudinal axis of the ymonitor wire 202. The shape in planview of the straps 216 is vvbest seen in Fig. 5, the straps being 'substantially rectangular `insl'1ape but having va semi-'circular cut-out 218 along one of Athe-"longer edges thereof, the cut-out 'being along 'the edge positioned inwardly of tube 200 and being positioned about the longitudinal center l-ine ofv tube 200.

The upper side of tube 200 'as viewed in Fig. 1 has an Ielc'mgated slot l220 formed therein through which monitor wire `202 lextends. Monitor 'wire 202 is xedly attached to the 'end of :a second tube 222 whose external diameter -is slightly less than the linternal diameter of tube 200 whereby 'tube 222 slides easily within tube 200. An abutment member 224 positioned on tube 222 extends upwardly through fsl'ot '220 and serves to center tube 222 with respect to slot 220 and `thus in turn centers the monitorwire202. The vother end of tube 202 carries a collar 226 viixedly 'attached thereto which includes the adjust-ing mechanism that will be described later.

Positioned within vtube 222 and slidable therein is a substantially cylindrical plunger 228. The left hand end of plunger 228 as viewed in Fig. l has Va longitudinal aperture therein which receives ra resistor 230. One en'd of resistor 230 is attached to plunger 228 in a part-circular depression therein as at 232 andthe other end- -of resistor 230 is connected to the pick-up loop 192. A longitudinal hole through `plunger v228 Areceives `'a co-axial cable 234 which has the 'center lead 196 therein attached to 'one end of the pick-up loop 192. The other end of the co-axial cable 234 is provided with the usual coupling 236. i

In the actual installation the 'end of the tube 200 carrying the electrostatic shield straps 216 is positioned adjacent tothe coil in the tank of a variable frequency oseillator. tI-t is desirable to adjust the radio frequency -iniection into the attenuator by moving the monitor Wire 202 and' the pick-niploop 192 toward and away Vfrom the shield and straps 216 and the associated feed coil. Also' ing the desired movement of tube 222 and plunger 228 The portion of tube 222 will be described in detail. which normally extends outwardly and to the 'right with respect to iiange 214 'as viewed in Fig. 2 has attached thereto by means of screws 238 a geared rack 240. A gear 242 mounted on a shaft 244 is provided vto engage with rack 240.

Shaft 244 is permanently positioned with respect to iiange 214 and a rotary movement of shaft 244 and the attached gear 242 causes-movement of tube 222 inwardly and outwardly with respect to tube 200. This accordingly adjusts the position of monitor wire 202 with 're` spect to the associated tank coil, this adjusting motion -being vaccomplished without aliecting the attenuation be- I y *waarnaar to tube 222 is mounted on the upper Aportion of member 226 as viewed in Figs. 2 and 3. A slot 246 is formed in plunger 228 at the righthand thereof as viewed in Fig. 2 and within the slot is mounted a geared rack v248 held in position by two screws 250. vThe highest point on the teeth of rack 248 is-disposed well within the circumference oftube 228. A slot is formed at the night hand end of tube 222 and into this slot extends a toothed gear 252 which cooperates and meshes with the teeth on .rack 248. Gear 252 is mounted on a -rotating shaft 254 which is journaled in a pair of bearing blocks 256. In order to insure that there is no lost motion in the gear and rack arrangement, a frame 258 is provided that supports a pair of springs 269 that are under compression. AThe springs 260 press against 'the bearing blocks 256 and thus `in turn press gear 252 against rack 248 to eliminate lost-motion and inadvertent misadjustment therebetween.

The attenuator of Fig. 1 through 5 insuresthat .only the desired excitation is obtained on pick-up loop 192, the desired excitation being that corresponding to the inductive coupling mode. This is obtained by providing the electrostatic shield Y 198 including the straps 216 `between the associated feed coil vof the RF tank and the pick-up loop 192. Since the electrostatic shield 198 is immobile and since the monitor loop moves behind the shield, there is practically no mistuning of the main RF tank including the associated feed coil due to the varia- .tions of the position of the monitor loop 202. Further- ,i

more, the amount of RF injection into the attenuator can 1be adjusted by turning shaft 244 without affecting the value of the attenuation Aand the value of the attenuation can Ibe adjusted by turning shaft 254 thereby changing the distances between pick-uploop 192 and the moni- Ist will be seen that there has been provided an attenuiator of the wave guide type which fulfills all of the adtvantages and objects set forth above. ciic example of the attenuator has been given for pur- Although a speposes of illustration, it is to be understood that various .changes can -be made therein without departing from the spirit-and scope of the invention. Accordingly, the in- .vention is to be limited only as set forth in the follow- .ing claims.

. We claim:

1. A radio frequency attenuator for operation with an `associated source of radio frequency radiation on the .inductive-coupling mode as a wave guide below cutoff, V`comprising a first tube adapted to have one of the open ends thereof disposed toward'and xedly positioned with .respect to the radiation source, said rst tube having a longitudinal slot therein, a second tube positioned within said first tube and being slidably adjustable therein, a

monitor member mounted on and carried by said second 'through said slot a distance that is small compared to 'the transverse dimension of said iirst tube whereby said monitor member is inductively coupled to the radiation jsource, means positioned in said one end of said rst K ,tube forming an electrostatic shield suppressing the capacitive-coupling mode' between said monitor member and the radiation source, a pickup member positioned within said second tube and being slidably 'adjustable ftherein to receive'radiation from said monitor member, lrst adjustment means to move said second tube including said monitor member and said pickup member si- ,multaneously with respect to said first tube to adjust the amount of radiation injected into said attenuator without changing the attenuation betweenv said monitor member and said pickup member, and second adjustment means to move said pickup member with respect to said 'monitor member without moving said monitor member .tube within said first tube and extending outwardly Y' .respect to the radiation source,

with respect to said rst tube whereby to adjust the attenuation between said monitor member and said pickup member without changing the amount of radiation injected into said attenuator.

2. A radio frequency attenuator for operation with an associated source of radio frequency radiation on the inductive-coupling mode as a Wave guide below cutoff, comprising a rst tube adapted to have one of the open ends thereof disposed toward and fixedly positioned with respect to the radiation source, said rst tube having a longitudinal slot therein, a second tube positioned within said rst tube and being slidably adjustable therein, a monitor member mounted on and carried by said second tube `within said lirst l,tube and extending outwardly through said slot a distance that is small compared to the transverse dimension of said rst tube whereby said monitor member is inductively coupled to the radiation source, an abutment member lixedly mounted on said second tube and extending into said slot and engaging the edges thereof to hold said monitor member spaced from the edges of said slot, a plurality of metal straps mounted across said one end of said first tube to provide an electrostatic shield suppressing the capacitive-coupling mode between said monitor member and the radiation source, a plunger positioned within said second tube and being slidably adjustable therein, a pickup member mounted on said plunger within said second tube to receive radiation from said monitor member, first adjustment means to move said second tube and said plunger simultaneously with respect to said rst tube thereby to move simultaneously said monitor member and said pickup member with respect to the associated radiation source to adjust the amount of radiation injected into said attenuator without changing theattenuation between -said monitor member and said pickup member, and sec- ,ond adjustment means to move said plunger with respect to said second tube thereby to move said pickup member toward and away from said monitor member without moving said monitor member with respect to said first tube whereby to adjust the attenuation between said monitor member and said pickup member without changing the amount of radiation injected into said attenuator.

3. The radio frequency attenuator as set forth in claim 2, wherein the monitor member is a wire, and the straps lare positioned along chordal lines of the first tube and are disposed perpendicular to the axis of said monitor -w1re.

4. A radio frequency attenuator for operation with an associated source vof radio frequency radiation on the inductive-coupling mode as a wave guide below cutoff, ycomprising a first tube adapted to have one of the open ends thereof disposed toward and ixedly positioned with said first tube lhaving a longitudinal slot therein, a second tube positioned Within 'said rst tube and being slidably adjustable therein, a

'monitor member mounted on and carried by said second tube within said first tube and extending outwardly through said slot a distance that is small compared to :the transverse dimension of said first tube whereby said .monitor member is inductively coupled to the radiation source, means positioned in said one end of said first tube forming an electrostatic shield suppressing the capacitive-coupling mode between said monitor member and the radiation source, a plunger positioned within said second tube and being f slidably adjustable therein, a pickup member mounted on and carried by saidplunger within said second tube and'positioned to receive radiationfrom said monitor member, rst adjustment means including a first rack and pinion acting between said first and second tubes to move said second tube including said monitor member and said plunger including `said pickup member simultaneously with respect to said first tube to adjust the amount of radiation injected into said Aattenuator without changing the attenuation between said t monitor member and said pickup member, and second adjustment means including a second rack and pinion one end thereof connected through a resistor to said acting between said second tube and said plunger to plunger and having the other end thereof connected to move said pickup member with respect to said monitor the center conductor in a radio frequency co-axial cable member without moving said monitor member with carried bythe plunger.

respect to said `i'irst tube whereby to adjust the attenuao References Cited in the me of this patent tion between said monitor member and said pickup member without changing the amount of radiation injected UNITED STATES PATENTS into said attenuator. 2,494,722 Rosen J an. 17, 1950 5. The radio frequency attenuator set forth in Claim 2,666,183 Ocnaschek Jan. 12, 1954 4, wherein the pickup member is a loop of wire having 10 2,701,863 Pierce Feb. 8, 1955

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