US3500253A - Uhf directional mixer - Google Patents

Description

March 10, 1970 J. G. OPRYSKO 3,

UHF DIRECTIONAL. MIXER Filed Jan. 2:5. 1968 2 Sheets-Sheet 1 INVENTOR.v JOSEPH GI OPR KS'KO Arron/m 2 Sheets-Sheet I I'll-0d Jill. 23, 1968 MULTl-CHANNEL INPUT COMBINED OUTPUT 0 1 I I. I I I gm l I I l I l SINGLE CHANNEL INPUT FIG. 2

INVENTOR. JOSEPH G. OPRYSKO 5 ATTORNEYS United States Patent 3,500,253 UHF DIRECTIONAL MIXER Joseph G. Oprysko, Philadelphia, Pa., assignor to Jerrold Electronics Corporation Filed Jan. 23, 1968, Ser. No. 699,817

Int. Cl. 1101 5/12 US. Cl. 3339 6 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Conventional mixers for UHF frequencies include a variety of types whose attributes generally reflect the particular function for which they were designed. With the advent of community antenna television systems (CATV systems) there has existed a demand for a mixer capable of mixing a predetermined channel frequency having a 6 mHz. wide signal into a coaxial line carrying other UHF TV signals. To date, no unit has satisfactorily fulfilled this function and simultaneously met the desirable qualities of being easily adjustable as to the channel frequency being coupled (single tuned); stable in impedance matching characteristics regardless of adjustment; and has the requisite ruggedness of CATV type devices.

It is also desirable to provide an arrangement wherein means are provided to guard against the possibility of the inserted channel (to be mixed in with the remaining UHF signals) also appearing inadvertently on the other input.

It is the object of this invention to achieve the foregoing with a device which is simple and economical to manufacture.

SUMMARY OF THE INVENTION Briefly, the invention is predictated upon the concept of a pair of intercoupled microwave cavities, one of which includes a band-reject pole (at the specific frequency to be mixed) and is fed with a group of UHF TV signals; and the other of which includes a band-pass pole at the same frequency, and is fed With a signal at that frequency. Directional coupler action is provided by the incidental magnetic coupling introduced !by the arrangement for cavity-to-cavity coupling.

The above mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will best be understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, the description of which follows.

DESCRIPTION OF SEVERAL VIEWS OF THE DRAWING FIG. 1 is an exploded perspective illustration of one embodiment of the invention, and

FIG. 2 is a schematic of the equivalent circuit of the embodiment shown in FIG. 1.

3,500,253 Patented Mar. 10, 1970 "ice DETAILED DESCRIPTION OF THE DRAWING In the description of the invention which follows, reference shall be made simultaneously to FIGS. 1 and 2. In these figures, similar reference characters are employed to designate similar elements.

The signals with which the invention is concerned consist of a group of signals, including a plurality of UHF TV channels, generally available over a first coaxial line, and a single channel to be injected into the group and available over a second coaxial line. The latter single channel signal, generally 6 mHz. wide, is fed to one microwave cavity 12, through push-on fitting 14 of input 1,. The signal is launched in the cavity by means of length L The group of UHF TV signals are applied to another cavity 16, through an input J which includes coaxial connector 15. The output, as will be explained, is available at J via coaxial connector 17.

As shown in the exploded perspective, the entire assembly is completely shielded in housing'20 having a resilient finger 21 for grounding and for rigidly maintaining the cavity exterior relative to the housing. Further mechanical support is provided by hexagonal nuts 23 and 24 on the adjustable capacitor studs C and C The cavities are coupled directly between input I and output 1;; by through line 10 and compensating capacitor C Cavity 12 includes a tuned band-pass pole at the frequency of the channel injected at input 1,. The tuned pole is provided by inductance L in series with adjustable capacitor C Inductance L employs its own distributed capacity to provide a resistive cavity coupling element in series with transmission line 10; the combination forming a shunt arm with element C Cavity 16 includes a bandreject pole similarly provided by inductance L in series with adjustable capacitor C and for a corresponding purpose further includes resonator L The specific 6 mHz. wide channel signal injected via input J meets the described band-pass filter L C tuned to this incoming channel frequency and it accordingly passes with low attenuation to output J At this juncture, it bears mentioning that the pass and reject poles have sufficient bandwidth and the skirt characteristics are such that the entire 6 mHz. signal may be considered as a whole.

The remaining UHF signals to be mixed which are injected into the other cavity via input J meet a band-reject pole at the frequency of signal being applied to input J Accordingly, signals on input J will be passed except where they correspond in frequency to the signal being applied to the input 1 Consequently, unwanted out-of-phase signals which may appear on the antenna or through an amplifier coupled to J will not be mixed with those appearing over J Further, due to the bandreject pole, the signal appearing on input 1 will not appear on input I via the cavity coupling line 10 from J1 t0 J2.

Transmission line 10 does, however, carry the signal from J to output J and since I also includes the magnetically coupled signal of input J the desired mix ing action is achieved.

Any number of channels may be be mixed by merely providing a number of devices of the invention equivalent to the number of channels to be singularly mixed and iterating the circuits in tandem. Since the cavities are tuned to the same frequency, one for band-reject, and one for band-pass, the cavities may be termedsingle tuned.

By employing the described arrangement, no incoming channels appear on another incoming line, yet both incoming signals appear on the outgoing line. Capacitors C and C are tunable to the desired frequency of the input J In addition, inductances L and L which are.

air core inductances of predetermined number of turns, may be manuallyadjusted by slight shifts in their position and spacing to precisely provide the desired reject and pass poles. Inductance L is adjusted for coupling into cavity 12 With the proper loading for the minimum loss in band width.

Directional coupler action is provided by the incidental magnetic coupling of through line connecting the cavities. In particular, this magnetic coupling is provided by the length of line in the right hand cavity which isshown slightly longer (exposed) than in the left hand cavity. This line length magnetically couples, as shown in phantom on the equivalent circuit, to inductance L and at the frequency of the cavity produces a current coupling opposite to the voltage coupling from J and results in a partial cancellation of signal between J and J creating amismatch which enhances the filtering provided by the trap pole L C The foregoing arrangement has the unique advantage of providing the conventional low loss of a directional coupler in the paths between J J and] J with the desirable attributes of band-pass, band-reject filtering which normally give much greater attenuation.

The following are exemplary parameters for a circuit according to the invention which is tunable over the UHF TV frequency range.

Cavity 12 and 14 dimensions5.08 6.67X254 cm. L and L 1.74 3.O8 cm.

L, (effective)2 cm.

L 5 turns No. 26, diameter L 1O turns No. 26, diameter C and C .759.5 pf.

While the principles of the invention have been described in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the score of the invention as set forth in the object thereof and in the accompanying claims.

What is claimed is:

1. A UHF mixer comprising:

a first microwave cavity;

coupling means for feeding an input signal into said first cavity;

coupling means for extracting an output signal from said first cavity;

a second microwave cavity;

means for feeding a second input signal to said second cavity;

means for tuning said second-cavity to reject a minor band embracing the input to said first cavity;

means for tuning said first cavity to' pass said minor band; and I means for coupling signals between said first and second microwave cavities, including a transmission line coupling said means for feeding a second input signal to the second cavity with said output signal coupling means in saidfirst cav-ity. 2. The UHF mixer claimed in claim 1 wherein said line includes a'magneti'c coupling component providing directional coupler action at the frequency of the cavities.

3. The UHF mixer claimed in claim 1 wherein said means for tuning said first and second cavities comprises an inductance and capacitance in series.

4."The UHF mixer claimed in claim 3 wherein the capacitances in each of said cavities is adjustable.

5. The UHF mixer claimed in claim 4 wherein the inductance in series with said adjustable capacitance in said first cavity comprises a linear element within said cavity and wherein the input coupling means in said cavity includes a linear element running in parallel therewith for a predetermined distance.

6. The UHF mixer claimed in claim 1, wherein said first and second microwave cavities have a common wall, and wherein said transmission line includes a wire passing through said common wall.

References Cited I UNITED STATES PATENTS 2,803,745 8/1957 Wen Yuan Pan et a1.

I 333-76 XR 2,816,270 12/1957 Lewis 333-73 XR 3,056,096 9/1962 Vane 333-76 XR 3,124,768 3/1964 Tilston 3339 3,252,095 5/1966. Carlson 33382 XR H. SAALBACH, Primary Examiner M. NUSSBAUM, Assistant Examiner US. Cl. X-R. 333-11, 73, 6

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