US1928408A - Shield for leads from micro-ray tubes - Google Patents

Description

Sept. 26, 1933'. A. G. @LAWER I 1,923,408

' SHIELD FOR LEADS FROM MICRO-RAY TUBES Filed NOV. 24, 1931 MOMM.

FIG. B

ADJU$TAELE SHIELD Ta I 4 IINVENTOR ANDRE o. cLAvlm ATTORZEY Patented Sept. 26, 1933 UNITED STATES PATENT; OFFICE SHIELD ron LEADS mom MICRO-RAY TUBES New York Application November 24, 1931 Serial No. 576,972

4 Claims.

This invention relates to signaling systems and more particularly to systems in which microray waves are used. Such micro-ray waves may be defined, roughly, as those lying between the limits of 100 centimeters and 1 centimeter, al-- though these limits may be exceeded in either direction.

In the production of such waves a tube of special construction is used and leads from the tube 0 carry the high frequency oscillations.

The object of this invention is to provide a shield for the tube and the high frequency leads which will reduce the radiation loss in this portion of the circuit.

The following patents disclose various means for producing and'detecting waves of this frequency and suitable circuits and apparatus for using them for signaling purposes:

British 344,448-Comp1ete accepted March 3, 1931.

19l331ritish 352,052Complete accepted June 29,

French 708,495-Dlivr May 4, 1931.

U. S. Patent No. 1,927,393 issued to Ren H.

Darbord, discloses improvements in such a system. I My invention may be used in connection with any of the devices disclosed in these patents, or with any other system of high frequency signaling in this general frequency range.

In the drawing, a specific system is disclosed in which my invention may be employed.

Fig. 1 is a cross-section of a tube for the production or detection of waves in this range, taken along the axis of its electrodes.

Fig. 2 is a cross-section of the same tube at right angles to Fig. 1.

Fig. 3 is a diagrammatic plan of the same cathode 4, concentric with which is positioned a helical grid or oscillating electrode 5, around which and concentric therewith is positioned a cylindrical reflecting electrode 6. The cathode is supported upon lead wires 7 and at one end is attached to a molybdenum spring 8 which keeps the cathode under suitable tension to prevent it from sagging and disturbing the electrical constants of the system. The reflecting electrode is positioned upon another lead wire 9 passing through the press 3. The helical oscillating electrode 5 is desirably supported from opposite ends by supporting lead wires 10 and 11 which are, in turn, mounted upon an insulating stem 12 carried by the press 3. Main lead or transmission wires 13 and 14 are connected to the supporting lead wires 10 and 11 and pass through the wall of the tube at seals 15, 16. These lead wires are electrically connected to the oscillating electrode 5 by means of the wires 10 and 11, and are preferably attached to the wires 10 and 11 by substantial fasteners, such as the threaded sleeves 17 and 18.

A specific tube may be constructed with the filamentary cathode 4 of pure tungsten wire 0.15 millimeters in diameter, with a length of approximately 22 millimeters, The helical oscillating electrode may consist of 20 turns of wire, preferably of refractory material such as tungsten, 0.22 millimeters in diameter, the turns having a diameter of 3.5 millimeters and the 20 turns having a length of approximately 20 millimeters, or one turn per millimeter. The reflecting electrode 6 may be a tube of any suitable material, such as tungsten, molybdenum or nickel, 7.5 millimeters in diameter, and 18 millimeters long. A tube having electrodes of this construction is well adapted for the generation or detection of oscillations at a frequency of 1,666,666 kilocycles corresponding to a wavelength of 18 centimeters. The voltages used are approximately as follows:

Oscillating electrode +300 volts Reflecting electrode volts Cathode .6 volts, 3 amperes in adjacent conductors of the line.

stantial departure therefrom is possible and a substantial range of different frequencies may be generated or detected in a tube of these dimensions. The dimensions of the tube itself are shown. on the drawing, Figs. 2 and 3. All the dimensions shown are in millimeters.

In Fig. 4 the tube 1 and oscillating electrode 5 are shown diagrammatically and the leads 13 and 14 therefrom are shown connected by a concentric transmission line 19 to a suitable antenna 20-21. The functions and operations uf the transmission line and antenna are disclosed in the United States patent above referred to.

This transmission line may be made of a copper wire surrounded by a copper tube with spacers of any suitable insulating material between them. The diameter of the internal conductor may be 2 millimeters and the internal diameter of the external tube may be 4, 6, 8 or 10 millimeters.

Since the leads 13, 14 are spaced 18 millimeters apart, as shown in Fig. 3, and it is desirable that these leads be parallel, the space between the internal conductor and the outside of the external conductor will have to be at least 18 millimeters.

The tubular line connecting the parallel transmission line to the radiatingsystem may be made of different parts as shown in Fig. 4 and explained in the United States patent referred to above. Part ab is variable in length, and has an outside diameter of twice the distance between the parallel wires which connect the tubular line to the tube. The inside conductor may be of any convenient size. Part cd is a three-quarter wave length line, the characteristic impedance of which, determined by the ratio of inside diameter of external tube to outside diameter of internal tube should be such as to match the impedance of the radiating system with the internal impedance of the tube. In a particular instance, for a tube used as a receiver, this optimum characteristic impedance has been obtained with a ratio of radii equal to 3.5. The sections be and de, being a wave length long, only act to transfer the state of Oscillations from their input side to their output side without appreciable change and may be made of conductors of any convenient diameters, preferably avoiding too big variations of diameters The mirror or reflector M may be of a paraboloidal shape, the diameter of the opening circle and being large compared with the wavelength, for instance 10 to 15 times the wave length, and may be a casting of aluminum. The radiator may be installed at the focus of said reflector, maximum efliciency of this electro-optical system being maximum when the focal distance of the reflector is equal to half the'radius of the opening circle of said reflector.

In the use of the system described above, it has been found that the radiation loss of the parallel wires 1314 between the tube and the concentric conductors is considerable. In earlier experiments such losses were not encountered because the antenna or doublet was connected directly to these leads and the entire tube and antenna structure was placed at the focus of the mirror. However, the previous arrangements were subject to other difficulties, as disclosed in the United States patent above referred to, so that it is desirable to separate the antenna from the tube with the use of the concentric transmission line disclosed therein.

Also, in certain cases it is advisable to use quarter wave length lines in such a way that the load impedance into which the parallel wire line looks becomes small. The current in the line may then assume a high value which is apt to produce a higher radiation loss than in former installations.

It has been found that these radiation losses can be eliminated by the use of a cylindrical shield co-axial with the axis of the transmission line. This is an entirely different type of shielding than that generally used on higher wavelengths, as it is designed to reflect the wave back to the parallel wires in opposite phase to the field which would be generated in the close vicinity of the transmission line if it were not for the presence of the shielding apparatus, and relies on the time taken by the wave to travel from the transmission line to the inside surface of the shielding box and back to the transmission line. result, the radius of the screening box has to bear a certain definite relation with the wavelength propagated along the transmission line. If an element of the transmission line is considered, the currents in the two opposite wires set up electric fields at a distance which are almost in opposite phase so that the resulting field is nearly 90 out of phase of the said-currents, so that if R is the radius of the screening box, the distance covered by the reflected wave is equivalent to A A 212+ This last is due to the advance of phase when reflection is produced on the inside surface of the screening box.

In order to prevent radiation loss, the equivalent distance considered above should be equal to an odd number of half wave lengths, which gives the law relating the radius of the screening box to the wave length. The radius should be very nearly equal to an odd number of of a wave length. In a particular instance in which the above device was used, in both transmitting and receiving stations the ultra short wave tubes were connected to a tubular line by means of a parallel wire line, as shown in Fig. 3. It has been found highly advisable to surround the line and even the tube itself by means of a cylindrical box the radius of which is, as mentioned above, equal to an odd number of eighth wave lengths, 5 in the particular case.

It is also advantageous to close the ends of the shielding apparatus with the same material as that used for the shield, which may be copper. The end of the shield at the transmission line may be connected directly to the external concentric conductor. These ends may be plane, as shown in Fig. 5. The shielding box is made in two sections. This is for the purpose of obtaining easy access to the tube by removing the outer section, and is also for the further purpose of adjusting the distance between the two ends of the shield. There is a particular adjustment of this distance for which best results are obtained. I am not prepared, at this time, to state the law governing this adjustment, but the best adjustment may easily be discovered empirically in each instance.

What is claimed is:

1. A micro-ray vacuum tube, leads from said tube, a cylindrical shield surrounding said leads, the radius of said shield being equal to an odd number of eighth wave lengths.

2. A micro-ray vacuum tube, an oscillating electrode in said tube, leads connected to said In order to achieve this oseillatina electrode, a transmission line coneighth wave lengths and comprising two telescopic neeted to said leads, and a cylindrical shield sursections each havlns one end closed. roundin: said leads, said shield having a radius 4. A micro-ray vacuum tube, leads from said equal to an odd number of eizhth wave lengths. tube. a cylindrical shield surrounding said leads,

5 3. A micro-ray vacuum tube, leads from said said shield havin: a radius equal to nve-eizhths 80 tube, and .a shield surrounding said leads, said of a wavelength.

shield-having a radius to an odd number or v ANDRE GABRIEL cmvnm.

is so so I 95 2s h Q 100 so 10s as 4 v Y 110

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