US2438521A - Crystal frequency converter - Google Patents

Description

w. M. SHARPLESS 2,438,521

CRYS TAL. FREQUEXiCI C IN ERTER March 30, 1948.

2 Sheets-Sheet 1 Filed Feb. 15, 1945 //v I/ENTOR By W M. SHARPLESS ATTORNEY March 30, 1948.

W. M. SHARPLESS CRYS TAL FREQUENCY CONVERTER Filed Feb. 15, 1945 2 Sheets-Sheet 2 INVENTOR WMSHARPLESS A TTOR/VEV Patented Mar. -30,v 1948 CRYSTAL FREQUENCY CONVERTER William M. Sharpless, Fair Haven, N. J assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application February 15, 1945, Serial No. 578,030

Claims. (01. 250-31) This invention relates to ultra-high frequency systems and particularly to modulators therefor such as first detectors or frequency converters in multiple detection radio receivers.

Many characteristics of the crystal type rectifying device have made its use very desirable in the microwave range, for example, at wavelengths ten centimeters and shorter. In my copending application Serial No. 483,607, filed April 19, 1943, now Patent No. 2,436,830, dated March 2, 1948, there are disclosed various technics for the efficient and effective use of this type of rectifier in this frequency range. One feature of converter design brought out in that application is the design and adjustment of the tuned input line to provide such a control of the relative amplitudes and phasing of the fundamental and harmonic components of the input Wave as to give an optimum relation between signal and noise output. In the specific structure shown in that application this tuned input line is of the coaxial type. For signals in the shorter wavelength portion of the range it is often more desirable to employ a wave guide rather than a coaxial line. While the same general design principles are applicable in such cases quite different methods of applying the principles are dictated by the structural differences.

An object of the invention is to provide the proper control of the phase of the fundamental and harmonic components in a wave guide input to a frequency converter.

Another object of the invention is to provide separate adjustable controls of the fundamental and harmonic terminations of a tuned Wave guide.

In addition to the problems arising directly from the electrical aspects of the converter design and operation there are certain aspects where the factors of mechanical design assume considerable proportions. One such problem is that of overcoming the difiiculty of removing and changing crystals. Because of the frequencies involved, the dimensions of the crystal and its associated contact point must be kept very small. While some of the difficulties arising from this fact have been overcome by permanently mounting the crystal in a cartridge, the same factors that limited the size of the crystal also impose limits on the cartridge size. This fact as well as the susceptibility of the crystals to damage by mechanical shock create a considerable problem in the mounting of the crystal so that when in place it will be firmly held with good electrical reproducible contacts and still be suscep- 2 tible of being readily removed so that it may be replaced in case of failure.

Another object of the present invention is to provide a mounting for the crystal unit of ultrahigh frequency radio equipment that will permit the ready removal and replacement of crystal units.

In accordance with a specific preferred embodiment of the present invention in a first detector or converter unit for an ultra-high frequency radio receiver there is provided a signal input system of the wave guide type with a crystal rectifier unit mounted across the guide which is terminated to permit adjustment of the relative phase of the fundamental and harmonic components of the signal input. This termination is provided by the use of a number of adjustable septa. One of these septa is so located as to divide the Wave guide into sections of such cross-section that the cut-off frequency of each is such that the fundamental frequency of the signal wave will not be transmitted. In so far as the fundamental component. is concerned such a septum has the same effect as a piston terminating the wave guide at substantially the position of the end of the septum. For the termination of the wave guide for the harmonic components there are provided other septa dividing the wave guide sections formed by the first septum into further compartments of such cross-section as to have a cut-ofi such that selected harmonics are not transmitted. By adjusting the individual septa the guide can be given different terminations for different component frequencies of the signal wave thus permitting such a proportioning of the phases of the fundamental and harmonics as will result in an optimum signal-to-noise ratio in the converter output.

The crystal cartridge is mounted through the wave guide. For this purpose a jack is provided in one wall of the guide and insulated therefrom terminating thehigh frequency circuit by a trap or filter and forming the intermediate frequency output circuit. The small end of the cartridge terminating the crystal contact point plugs into this jack. The other terminal of the crystal cartridge is held by a screw operated chuck mounted in the opposite wall of the guide. In order to facilitate the insertion and removal of the crystal cartridge there is provided an elon gated handle member with aspring chuck at the end which engages the base of the cartridge at a position removed from the point at which it is held in the screw-operated chuck.

These as well as other objects, features and aspects of the invention may be better understood by reference to the following detailed description in connection with the drawing in which: I

Fig. 1 is a perspective view of a crystal converter embodying the invention;

Fig. 2 is a cross-sectional view of the cone verter of Fig. 1 on an enlarged scale; and

Fig. 3 is an exploded view of the crystal holder of the converter of Figs. 1 and 2.

The converter comprises a main body in the form of a wave guide section H). A flange II is provided for connecting to thewave guide system (not shown) of the receiver through which the signal and beating oscillations are introduced into the converter.

The wave guide I is terminated bymeans of the septa |2, I3 and I4 extending into the rear end and parallel to the short walls of the guide. These septa are arranged to make good contact with the bottom and top of the guide. For this purpose each septum is formed of two curved strips of resilient material mounted back to back with their edges riding in milled grooves in the Walls of the guide, as shown. The effect of the septum I2 is to dividethe guide into two sections .of such dimensions that the cut-ofi frequency of each section is above the fundamental frequency of the input signal wave. This septum therefore acts to terminate the guide for this fundamental frequency in much the same way as if the guide were terminated by a shortcircuiting piston at a point near the inner edge of the septum. The two smaller wave guide sections on each side of the septum l2 have such dimensions that harmonics of the signal wave may be transmitted therethrough.

The septa |3 and Hi serve to divide the two wave guide sections formed by the septum I2 and to terminate those sections for higher frequencies in the same way that the septum |2 terminated the main wave guide for the fundamental signal frequency. Since all of the septa I2, is and I4 are individually adjustable it is possible not only to adjust the effective length of the wave guide for the fundamental frequency but also independently for harmonic frequencies. Thus by the adjustments of the secondary septa l3 and M the phase of the reflected harmonics may be varied.

While three septa equally spaced across the guide are shown here it should be understood that a different number of septa with other spacings may be employed depending upon the design factors in any particular case.

The crystal element is mounted through the wave guide at an appropriate point. It has been found that the positioning of the crystal sidewise in the wave guide controlled the effective conductive loading to the guide of the crystal. The most effective position for any particular construction may be determined. by experiment. As shown in Fig. 1 it will usually be found to be somewhere oif the center of the guide. For con- The intermediate frequency output coaxial line 30 comprising an outer sleeve 3| which has a threaded shoulder portion at one end that screws into a threaded hole in the wall of the wave guide l0 forming a flush surface with the inner surface of the wave guide wall. The main outer conductor is secured to the other end of the outer sleeve 3| by means of the threaded locking ring 33. The inner conductor 34 is provided on one end with a spring contact jack 35 which receives the tip 24 of the crystal cartridge. At an intermediate point on the inner conductor 34 a skirt 36 is secured thereto. The open end of the skirt 36 is flanged. This permits the inner conductor to be 'mounted within the sleeve 3| by being clamped between the washers 31 and 31A against a shoulder on the inner surface of the sleeve 3| by means of the locking ring 38. The outer end venience in handling and replacement the crystal 22 is permanently mounted in a cartridge 20. This comprises a base member2| to which the crystal 22 is attached, an insulating sleeve 23 and a tip member 24 to which the crystal contact 25 is attached. Mechanical support for the cartridge 20 as well as electrical connections to the crystal are provided by the intermediate frequency output coaxial'line 30 and the crystal holder 40.

of the conductor 34 is supported by an insulator 39 spun into the end of the outer conductor 32. A hole in the outer end of the inner conductor 34 and a shoulder in the outer conductor 32 permit the attachment of a section of flexible coaxial line (not shown) leading to the intermediate frequency amplifier.

The length offltheskirt 33 is substantially ,onequarter wavelength at the frequency of the signal wave so that it forms a trap or filter for the signal currents preventing their transmission through the line 33 while permitting the transmission of currents of the intermediate frequency as is understood in the art. The length of the jaw detail is also a quarter wavelength so the complete assembly is'eifectively a double: quarter wavelength trap, giving a low impedance or short-circuit for the high frequency at the wave guide surface.

The crystal holder 43 is shown not only in the sectional View of Fig. 2 but also in the exploded view of Fig. 3. An outer sleeve 4| has a threaded shoulder at one end which screws into a hole in the outer wall of the wave guide [0 diametrically opposite to the hole into which the sleeve 3| is threaded. A slotted chuck 42 is carried inside the sleeve 4! bearing against thetaper seat 43 into which thechuck 42 may be clamped. A tubular member 44 is provided near its inner endwith an enlarged threaded portion 45 that screws into the internally threaded outer end of the sleeve 4 I. A knurled tube 45 press-fitted over the opposite end of the member 4!! provides a grip by. which the member 44 can be screwed into the sleeve 4| to press the check 42 into the seat 43 clamping the crystal cartridge or loosened to free the cartridge; A locking ring 47 threaded into the end of the sleeve 4i limits the movement of the member M preventing its removal.

There is also provided a handle48 for inserting andremoving the crystal cartridge. This handle is provided with a plurality of slots or 'saw cuts 59 and its inner end is shaped to pro: vide. agripping jaw 50. In the process of installing acrystal cartridge the handle 48 is removed from the assembly and the end of the cartridge inserted in the jaw 50. The handle 48 is then manipulated to insert the cartridge through the tube 43 until its tip 24 is engaged in the jack 35. The tube 44 is then screwedin forcing the chuck 42 against the seat 43 so that the head 2| of the cartridge is gripped by the chuck 42 establishing a firm mounting for the cartridge and good reproducible electrical connection to the crystal. A spring tongue 5| in the wall of the tube 44 prevents a rattling movement of the handle 48.,

It is to be understood that the present invention is not limited to the particular design shown here for the purpose of illustration and is capable of various modifications. In particular, the crystal holder is not limited in its application to a guide with the septa termination but may be used with the usual solid termination of the wave guide. Also if it is desired to eliminate the harmonics or to reduce their amplitude instead of reflecting them back into the guide, the metallic septa may be replaced by septa composed wholly or partly of resistance material.

What is claimed is:

1. A crystal converter comprising a rectangular wave guide, a plurality of septa extending into one end of said guide parallel to the narrow wall thereof, a cylindrical crystal cartridge having a tip end of reduced diameter, a spring jack mounted in one wall of said guide, a sleeve member mounted in the opposite wall thereof and having a taper chuck set in its inner end and being internally threaded, a spring chuck mounted in said seat, a threaded clamping tube carried by the internal threaded portion of said sleeve for clamping said chuck in said seat, and a bandle member fitting within said clamping tube and provided with a spring jaw at one end for gripping the large end of said cartridge so that said cartridge may be inserted through said chuck so that said tip end engages said spring jack.

2. In combination, a wave guide, a translating device associated with said wave guide, and

dimension of said guide extending longitudinally therein from one end and separately adjustable in their longitudinal positions, and so spaced as to divide said guide into a plurality of portions having cut-off frequencies higher than harmonics of the operating frequency.

5. In a crystal cartridge holder a sleeve member having an inner seat, a spring chuck carried in said seat, a tubular clamping member threaded on the inner surface of said sleeve member for clamping said chuck in said seat, and a handle member having a spring jaw at one end for gripping the crystal cartridge and adapted to be inserted within said tubular clamping member to insert and remove the crystal cartridge from said spring chuck.

WILLIAM M. SHARPLESS.

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