US2460476A

US2460476A - High-frequency potential dividing termination

Info

Publication number: US2460476A
Application number: US537509A
Authority: US
Inventors: Howard J Tyzzer
Original assignee: FERRIS INSTR LAB
Current assignee: FERRIS INSTR LAB; FERRIS INSTRUMENT LABORATORIES
Priority date: 1944-05-26
Filing date: 1944-05-26
Publication date: 1949-02-01
Anticipated expiration: 1966-02-01

Description

' 1949- H. J. TYZZER ,476

HIGH-FREQUENCY POTENTIAL DIVIDING TERMINATION F-iled May 26, 1944 HOWARD J. TYZZER INVENTOR ATTORN EY Patented Feb. 1, 1949 HIGH-FREQUENCY, POTENTIAL DIVIDING TERlVlINATION' Howard J. Tyzzer, Caldwell,

N. J., assignor to Ferris Instrument Laboratories, Boonton, N. J

a corporation of New Jersey A ueatmn May 26, 1944, Serial No.- 537,509 Claims. (01. 178-44) My present invention broadly relates to dividing electrical potentials into lower potentials, and more specifically to so dividing such potential developed by electrical alternating currents.

An object of my present invention is to divide potential developed at the output end of a line or cable employed to transmit electrical alternating currents where certain technological reasons in cases of'such transmission require that the line or cable be terminated in an impedance substantially equal to the characteristic or surge impedance of the said line or cable, in connection with which preserving the effects of the specific form of output termination is essential.

1 One particular object of my present'inven'tion is to make it effectively usable with a terminated signal generator output cable having the attributes disclosed in Ferris Patent 2,265,637 of December 9, 1941, including in particular the substantially uniform distribution of its inductance and capacitance attribute disclosed thereby.

A particular service renderable by such a terminated cable signal generator is the one of using the alternating potentials developed in its output termination element, which potentials are d,- rived from the electrical alternating currents generatedwithin the signal generator, to dependably check and determine the electrical alternating potential, responsive characteristics of devices, such as radio receivers, as .fast as built in order to be certain that the respective unit building of such devices has closely followed the responsive objectives of the specific design and/or model of thesame. This service now has to cover checking responsiveness to electrical alternating current potentials ranging in frequency from fractions of a megacycle to ultra high frequencies represented by hundreds of megacycles in respective comprehensive bands of frequenc-ies in accordance with the respective services the respective devices are designed to render.

As the frequencies of the electrical alternating currents with which one has to deal in the cases of these practices increase, the matter of maintaining dependability within reasonable tolerances becomes more and more stringent, with the result that what proved to be satisfactory a year or so ago fails to measure up to present day requirements. The shorter the signal generator output cable of the Ferris patent, supra,'can be, the less stringent is the matter of maintaining the desired dependability, but because of the usual Work bench conditions that must be taken into:

consideration in the fast use that goes on in doing said checking of performances, nothing less than a 15-foot long output cable has so far been ofiered to the public. Accordingly, in those cases that have arisen of the stringencies having to do with maintaining dependability of results as the demands for such services at higher and higher ultra high frequencies have acceleratedhnding the answers for the same by shortening the output cable has been frowned upon.

The object of the Ferris patent, supra, in its terminating of the signal generator output cable is the one of minimizing the development therein of undesirable reflections or the energyitranse mitted to the terminatin impedance'common to improperly terminated output elements, the need for which becomes more and more essential as thefrequencies of the now growing more common uses of ultra high frequencies are increased, so

that it'has becomedecidedly more important to 7 do nothing upsetting to the said proper termination in making use of the signal generators involved.

In using terminated lines or cables, and especially in those uses calling for signal generators, it often happens that the total output potential across the usual terminating resistor is either not wanted or can be helpfully reduced in the case of the particular work on hand, in Which'cases it is all important to effectively maintain proper termination irrespective of the particular connections made to obtain the reduced potential It is this object to which my present invention is directed, the necessary substance of which is here inafter described with the aid of the single illus-,

comprising closely spaced double conductors consisting of the line element C centered in a conductive sheathing G2, the former being equipped with a flexible insulating covering.

across indicated difference of potential points of an indicated resistance potentiometer P in cir-' cuit with an indicated generator of electrical alternating currents, A. C., which, in all signal generator cases would be of the usual vacuum tube and Circuit type, and may have in circuit therewith the indicated modulator M in case a modulated electrical alternating current is needed or desired, with it being indicated by the arrow that the frequency of electrical, alternating current These two conducting mediums are respectively connected" generation is variable. These elements are all located at the input end of the cable involved.

The output end of the cableis indicated as being generally terminated in a block B which will be fully described further along in this description. The conductors C and G2 per se are indicated as terminated in terminals HI and GT, respectively, having a resistance element R4 interposed therebetween. A third terminal LO has interposed between it and terminal HI a resistance element R and an inductance element L in the order named, and between it and terminal GT are connected three resistance elements RI, R2 and R3 in paralleled relation.

The block B is of conductive material, preferably aluminum, ments R4, R, L, Rl, R2 and R3 in appropriately configured recesses extending into the body thereof from the bottom which preferably has a bottom cover made of an appropriately shaped sheet of the same material. The recessed elements may all be of self-insulating types.

The terminals HI and LO are of conductive material set in holes spective locations of the block B indicated as fitted with insulated bushings, with the respective connections therefrom to conductor C and the other elements involved being made, as by soldering, before the bottom is closed. Terminal GT, however, is given a conductive relation to block B in order to be maintained in conductive relation to the outer end of conductor G2 through the body of block B as indicated by the broken line Gl. The broken line G3 indicates thatthe input end of the conductor G2 begins at one end of the potentiometer P; the housing H indicates that the AC generator is preferably isolated from the output cable and any device being checked, which necessitates a housing of effective shielding such as is aluminum; and the arrow A indicates that the value of the potential of the electrical alternating current supplied to the cable is controllable.

In quantity production of signal generators, common sense dictates the adoption of a construction of output cable that can be depended upon to have in the particular length adopted a substantially uniform characteristic or surge impedance in order that proper uniform termination may be had in resistors of the right ohmage of standard construction. For the purpose of giving details of as to how to apply my present invention to quantity production of signal generators I adopt a characteristic or surge impedance of 30 ohms for the output cable as typical.

Referring to the drawings, if a device to be checked for ascertaining its performance characteristics has its input leads connected to terminals HI and GT, respectively, this choice including terminal HI means that the highest available output potentials are to thereby be brought to bear for the particular checking involved; where as, if such input leads are connected to terminals L and GT, respectively, this choice including terminal LO means that some lower order of available output potentials are to' thereby be brought to bear for the particular checking involved. In this connection, I confine my treatment of the lower order of potentials involved to a connection because this percentage has been found to be a reduction in working output potentials cases of checking the performances of devices calling for lesser potentials than the higher pomost suitable to general needs in the thick enough to house the ele- V drilled in the indicated retentials considered for so long to be low enough for all checking.

This making of connections for such lower potentials has the advantage of causing less upsetting of the proper termination of the output cable that unavoidably arises out of bringing to to bear the load of the input of any device connected to the terminals for checking on the vital output cable proper termination calculations because it is clearly apparent that the upsetting reactions thus introduced into the terminating impedance are thereby reduced to about 10% of what they would be if the connections were made to terminals HI and GT, respectively, for highest potentials; Also, because of such connections for low potentials limiting thepickup ability of the input leads of any device being checked, the operation is automatically made less susceptible to pickups of extraneous signal generator leakage fields and fields of other sources that may be due to other electrical activities beyond control.

Heretofore, such output cables have been.

limited for termination to two terminals; such as HI and GT, having interposed therebetween, as shown by R4, a resistor selected to be as pure a resistance as modern construction will permit having a resistance ohmage value substantially matching the ohmage value of the characteristic or surge impedance of the cable it terminates,

but to make the practice of my invention applicable to a 30 ohm cable, for 30 ohms for resistor R4. 7

As shown, the resistances Rl, R2 and R3 interposed between the L0 and GT terminals are connected. in parallel, and with each of them having a resistance they, in their paralleled relation, collectively ofler a resistance ohmage value of the order of 3.3. However, even though these units are selected to have in their way of being made up a minimum of inherent inductance, and are connected in parallel to minimize their combined inductive efiect, the residual inductive reactance resulting therefrom, particularly at frequencies of the order of 200 megacycles in which I am particularly interested, is suihcient to actual working impedance appreciably more than their pure resistance of the order of 3.3 ohms in participating in the proper output cable termination for the purposes involved. 7

Because of output cable designing on the basis of making available 10% of the total output voltage for connections to the LO andGT terminals, it is obvious that in order for this to be accomplished the leg of the network comprising resistance R and inductance L in series must have nine times the impedance established between terminals L0 and GT. With the resistance ohmage of R made 30 ohms, I bring about the obtaininent of the required impedance ratio of 9 to 1 by giving to inductance L such an inductive value that combined with the inherent inductive value of resistance R this procedure requirement is satisfied. Although this brings about a pure resistance of about 38.3 ohms in parallel with the ohms of Rt, the increase of impedance.

due to the inherent inductance of the resistance elements added to that of the resultant impedance so that it, in parallel with the 60 ohms of R4, brings the total load of termination of involved down and closely to the 30 ohms of impedance at ultra high frequencies,. the correct. match of impedance for the particular cable. It a I substitute 60 ohms ohmage value of 10 ohms' make their consequential inductance L makes J far above 33.3 ohms the output cable a those imposed by the scope them from upsetting damage, they are kept from effectively radiating interfering components of the electrical energy with which they are necessarily activated.

While I have made known the nature of my present invention in certain confined respects, it is apparent that modifications may be made, and that no limitations are intended other than of the appended claims.

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

1. In an electrical system for transmitting electrical alternating currents for the purpose of remotely developing ing potentials from which to abstract working therewith electrical alternat potentials considerably lower in value, in which i:

system the frequencies are so high that the inherentj distributed inductances of the potentialdeveloping elements necessary thereto .must be taken into account in order-that the developed working potentials may be sufficiently dependable for said purpose; the combination of a double conductor transmission line terminated by an impedance that remains substantially equal to the characteristic impedance of said line which also has substantially uniform distribution of its inductance and capacitance, said impedance comprising a resistor interposed between the terminating ends of said line having an ohmage value materially in excess of the ohmage value of said characteristic impedance of said line, a multiplicity of paralleled resistances having appreciable inherent inductance at the operating frequencies interposed between the terminating end of one of said conductors and a terminal, and

- a resistance interposed in series with an inductance element between said terminal and the terminating end of the other one of said conductors, the resultant inductance of said inductance element and any inherent inductance in said series-connected resistance bearing substan- 40 ment is of tially the same ratio to the resultant inherent inductance of said parallel resistances as the ratio of said series-connected resistance to the resultant resistance of said paralleled resistances, and the summed up impedance of said paralleled resistances and the resistance in series with the inductance element being such that in parallel with the resistance interposed between the terminating ends of said conductors it establishes an impedance therebetween approximately equal to said characteristic impedance of said line, whereby the potentials developed across said paralleled resistances can be put to work without materially upsetting the required termination of said transmission line.

2. The system of claim 1, in which the ohmage value of the resistance interposed between the terminating ends of the conductors is substantially double the ohmage value of the characteristic impedance of the transmission line.

3. The system of claim 1, in which the ohmage value :of the resistance in series with the inductance element is substantially equal to the ohmage value of the characteristic impedance of the transmission line.

4. The system of claim 1, in which the in parallel impedance of the paralleled resistances is substantially equal to one-tenth of the total impedance arising from the in parallel impedance of the paralleled resistances plus the impedance of the in series resistance and inductance.

5. The system of claim 1, in which the characteristic impedance of the transmission line is of the :order of 30 ohms, the resistance of the resistance interposed between the terminating ends of the conductors is of the order of 60 ohms, the in parallel resistance of the paralleled resistances is of the order of 3.3 ohms and the resistance of the resistance in series with the inductance elethe order of 30 ohms.

HOWARD J. TYZZER.

45 file of this patent:

UNITED STATES PATENTS Name Date Ferris Sept. 27, 1938 Number