US1650353A - Wave signaling system - Google Patents

Description

Nov. 22, 1927.

L. A. HAZELTINE mwz smmum SYSTEI Orizinal Filed Feb. 27. 1925 pi INVENTOR lawkjiflnzeI/lbc find, mAwkw Patented Nov. 22, 1927.

UNITED STATES PATENT OFFICE.

LOUIS ALAN HAZELTINE, OF HOBOKEN, NEW JERSEY, ASSIGNOB TO HAZELTINE COR- PORATION, A CORPORATION OF DELAWARE.

WAVE SIGNALING SYSTEM.

Original application filed February 27, 1925, Serial No. 12,000, and in Canada May 4, 1925. Divided and this application filed January 4, 1927. Serial No. 158,839.

This application is a division of my copending application Serial No. 12,000, filed February 27, 1925.

This invention relates to wave signaling systems, particularly radio receivin systems, and has for its object the provision of a radio receiver which is highly sensitive and highly selective and at the same time is simple to control. This result is accomplished primarily by employing tuned radiofrequency amplification, preferably in more than one stage, with the complete elimination of couplings between the plate circuits and the grid circuits, except through the mutual conductance of the amplifying vacuum tubes, which when they include three electrodes are sometimes called triodes, and with an arrangement of the am lifier transformers so that their input con uctances are related in a certain way to the conductances of the vacuum tubes. Other features of the invention have to do with particular arrangements of the apparatus in ways that are both convenient and efiicacious, as will appear in the discussion which follows.

The elimination of coupling between the plate circuits and the grid circuits is accomplished by the cooperation of three steps: first, the arrangement of the amplifier transformers so that there is no magnetic coupling between any two of them; second, the avoidance in the wiring of any substantial.

impedance common to two or more tuned circuits; and third, the neutralization of the natural capacity coupling inherent between the tuned circuits, including particularly that due to the capacity between the grid and the plate of the vacuum tube.

The elimination of undesirable coupling between the plate and rid circuits results in the prevention of fee -back or regenerative action; and consequently there is no tendency towards the production of local oscillations. Such regenerative action is most troublesome with sharply tuned circuits and at high frequencies.

The proper input conductance of the amplifier transformers is obtained by employing a primary winding of fewer turns than has previously been the practice. The results are: (1) high selectivity; (2) substan tially complete neutralization of capacity coupling over a wide range of frequency with fixed neutralizing adjustments, even though there be slight unavoidable deviations from the ideal conditions for neutralization; and (3) higher amplification than is obtained with the large number of primary turns previously customary.

Referring to the drawings:

Figures 1 and 1 show a plan and an elevation, respectively, of a tuned radio-frequency amplifier embodying the features of this invention.

Figure 1 shows the diagram of connections of the receiver of Figures 1 and 1.

Figure 1 shows the structure of the radiofrequency amplifier transformers of Figures 1 and 1.

Figure 1 shows a modification of the circuit of Fig. 1.

In the radio receiver represented in Figures 1* and l there are three radio-frequency transformers T,, T T each associated with a tuning condenser C C C Each coil is mounted on the back of its condenser for the purpose of keeping as short as possible the leads between them, and for other purposes as disclosed in my U. S. Letters Patent No. 1,577,421, and in my pending application Serial Number 40,488, filed June 30, 1925. The vacuum tubes are -mounted adjacent to the coils and condensers with which they are associated, also in order to keep the connecting leads as short as possible. The coils of each transformer are preferably of the single-layer type. as illustrated in Figure 1, and are mounted with axes parallel and at an angle of substantially 55 degrees with the line of centers, this being a convenient arrangement resulting in zero magnetic coupling between any two of the transformers, as described in my patent and copending application above referred to. Care is also taken to avoid magnetic coupling between stages that might be due to closed conducting loops linked with the fields of two or more transformers. Such loops might exist in a supporting metal frame-work, or in the leads from the batteries, which leads are therefore preferably bunched together.

Figure 1 shows the diagram of connections for the receiver of Figures 1 and 1". The reflex principle is employed by which radio-frequency amplifying tubes A and A, serve also as audio-frequency amplifying tubes through the use of two audio-frequency transformers T and T The jacks J J,, J 2 enable a head telephone receiver or loudspeaker to be plugged in the plate circuit of the detector tube or either of the audio-frequency amplifier tubes.

Since each coil of an audio-frequency transformer has a high impedance to radiofrequency current, by-pass condensers C C are arranged to provide low-impedance return paths for the radiofrequency grid and plate currents direct to the respective filaments, or cathodes. This keeps radio-frequency currents out of the common battery leads, which may have sufficient reactive impedance as to cause objectionable coupling if they carry radio-frequenc currents of different stages. The grid y-pass capacities C C may be of the order of one ten-thousandth niicrofarad. and the plate by-pass capacities, U C C may be of the order of one thousandth microfarad, these values giving low radio-frequency impedances but sufiiciently highaudio-frequency impedances not to shunt unduly the audio-frequency transformer coils and so lower the audio-frequency aniplification. The leads to the by-pa'ts condensers should be short to minimize their reactive impedances.

In case the radio-frequency current in the plate circuit of detector tube D passes in a preciable amount through the primary of 1 and so couples tube D with tube A,, then a radio-frequency impedance L (Figure I? may be inserted in the lead from the plate 0 tube D, and a condenser C may be connected directly from this plate to the filament. Care must be taken that the impedance coil L is not coupled magnetically to any of the radio-frequency transformers.

The filament system should be grounded, preferably at X, Figure 1, S6; that radio-frequency current passing from the antenna through the natural capacity between the coils of T will flow directly to ground and not through the battery leads to the other tuned circuits and thence through their natural capacities to ground, which would resuit in undesirable coupling between the stages.

Coupling between the plate circuit and the grid circuit of tube A,, due to the natural capacity C between the grid with its connected apparatus and the plate with its connected apparatus, is neutralized by the neutra'lizing capacity C connected between the grid and the auxiliary coil ab, which in Figure 1 is a portion of the secondary coil (1.0 of transformer T As explained in my U. S. Letters Patents No. 1,489,228 and No. 1,533,- 858, neutralization will be effected when the primer coil ale and the auxiliary coil ab are coupl electromagnetieally and have terminals a and e which connect to the filament system, of opposite polarity, and when the ratio of the number of turns of ab to the number of turns of de is equal to the ratio of C to 0,1 The same arrangement and relation applies, of course, to the neutralizing capacity C11 and the output transformer T associated with the second amplifier tube A,.

Figure 1 shows the construction of the transformers T, and T The primary winding de is mounted so as to have close mag netic coupling to the tapped portion cab of the secondary coil ac, the tap 6 connecting to the neutralizing condenser C or C as shown in Figure 1. To make the coupling as close as possible between the auxiliary coil ab and the radio-frequency plate circuit, the leads from d and e and the leads to the plate by-pass condenser C or C Figure 1, should be made as short as possible. Such closeness of coupling is needed because the radidfrequency current flowing conductively through the plate of the vacuum tube would build up an appreciable voltage in the leakage reactance of the plate circuit, which voltage would not be balanced by a voltage in the auxiliary coil ab. The primary and secondary coils in Figure 1 are wound in the same direction, with the result that terminal a connecting to the filament system, Figure 1, is of opposite polarity to terminal e also connected to the filament system, (or, in other words, the low-potential terminals 0 and e are of opposite polarity, and the same is therefore true of the high potential terminals c and d) as required for the purpose of neutralization. The connection of the neutralizing condenser to a tap b so that a?) is a small portion of the secondary winding allows close coupling to be obtained between ab and ale and at the same time requires the primary windin r dc to extend under only a small portion 0% the secondary thus minimizing natural capacity and dielectric loss due to the dielectric field between primary and secondary. The primary windin as indicated, is placed adjacent to the lament end a of the secondary winding, for the same purpose.

In general there will exist natural capacity between the apparatus connected to the grid of A, and apparatus connected to the grid of A Such natural capacity has a neutrallzing tendency and so in part supplants C This neutralizing capacity is relatively more effective, for a given value, as the ratio of turns of ac to (Z6 is greater than that of ab to dc. Since do is not so closely coupled to de, such neutralization is not ideal and therefore should be minimized. This may be accomplished by making as short as possible all leads connecting to the grid, and by employing tuning condensers of the shielded type or a grounded metal plate on the back of the panel. Other grounded con- 1,eso,eas

doctors, such as the battery leads and the audioequenc transformers, interposed in the dielectric elds between the tuned circuits also serve as partial shields.

On account of the difiiculty of accurately measuring or calculating very small capacities, particularly natural capacities, the proper neutralizing capacities and C igure 1, are in practice determined by trial. A suggested procedure for neutralizing is as follows: First, with the filament of A cold and those of A, and D lighted, a strong signal is tuned in, as heard on a telephone receiver plugged in the detector plate circuit; C is then adjusted until the signal disappears, showing that no coupling exists between the glialte circuit and the grid circuit of A,. on with the filaments of D and A, lighted and that of A, cold, the process is repeated with G On account of the proximity of the radiofrequency transformers to one another and more especially of the presence of a loop formed by the leads between each secondar and its tuning condenser, the actual coil inclination for zero magnetic coupling may difler sli htl but appreciably, from its theoretic va ue of substantially 55 degrees. Hence, the proper inclination must also be determined y trial, and may be in accordance with the followin procedure. With all coils at the same inclination, Cu, and Cn are adjusted for zero coupling as described in the preceding aragraph, with the circuits tuned first or a low frequency and then for a hi h fre uency. In general, the settin foun for t e two frequencies will be di erent, showing that the capacity coupling, which varies with the frequency, is being called upon to compensate for some magnetic coupling. The coil inclinations are then varied together, until the settings of C and C are found to be the same at the two extreme frequencies.

The determination of the proper coil angle need ordinarily be made only once for a given design of receiver, but the adjustments of the neutralizing capacities are made in each individual receiver.

The use of short grid leads, the separation of the tuned circuits, and the interposition of grounded conductors, all serve to minimize the natural capacity coupling between T. and T Fi re 1. In addition, the antenna lead-in s ould be kept, as indicated, at the end of the receiver remote from the circuit of T and ungrounded conductors should not be allowed to extend from the neighborhood of T, to the neighborhood of By taking these precautions, the natural capacity coupling between T. and T, maybe substantially eliminated, and so need not be neutralized.

When the telephone receiver is plugged into the third jack J,, the plate and grid circuits of the tube A, will have the same natural audio fre uency if the transformers T, and T. are a ike. This would tend to give considerable audio-frequency re enera-' tion due to the coupling capacity between the plate and the grid of A,. This coupling ca acity will be neutralized by C for audio requency, provided the ratio of turns in the audio-frequency transformer T is the same as the ratio of turns of ab to tie and its relative polarity is as indicated, that is, the same condenser serves to neutralize capacity coupling both at radio frequency and at audio frequency.

We will now consider the proper value of the efiective ratio 1- of secondary turns ac to primary turns de in the amplifying transformers. (By efl'ective ratio is meant the ratio that would give the same mutual inductance with the same secondary self-inductance if the coupling between primary and secondary had a coe cient of unity. f the coupling is actually less than unity, the number of primary turns must be correspondingly increased relative to the number of secondary turns.) The amplification for one stage is given by the expression ills 9.1 m0.- unit)? 99 99 9! (2) which has its maximum value when Since at reasonance the input conductance of the transformer is equal to rg., the last condition ma be expressed in the form: that the amplification at resonance is a maximum when the ratio of turns of the transformer is so chosen that the input conductance of the transformer is equal to the plate conductance of the vacuum tube. If the number of primary turns is reduced below this value, the amplification falls off, but less rapidl at resonance than at other frequencies. or example, if the number of rimary turns is halved relative to ts value or maximum raonant amplification, the amplification at f uencies far from resonance is also halved, ut the amplification at resonance is reduced only twenty per cent. The result is a decided gain in selectivity,

since interfering si als are weakened proportionately more t an the signal tuned in. Thus to obtain high selectivity together with good amplification, the ratio of turns 1- should be so chosen that the input conductance T 9, is substantially, but not greatly, higher than the plate conductance 9,.

The following values are representative of present day practice in radio telephone broadcast reception:

1 10 5 radians per microsecond; L,=0.25 millihenry;

The amplification at resonance is then \Vit-h the form of transformer shown in Figure 1, the following design data will give constants approximating those listed in the preceding paragraphs: secondary cm], 60 turns of No. 24 A. W. G. double-cottoncovered copper wire wound close] on a three-inch cylindrical tube of good d1electr1c material; primary coil, 8 turns of the same or smaller wire wound on a 2.7 5 inch tube and spaced so as to lie under the tapped portion of the secondary coil.

The transformer T, preferably has a like secondary coil to T and T,, but its primary coil usually should have more turns especially if the antenna to be empilpyed is of small capacity and resistance. ith a considerable step-up ratio, the capacit and resistance of the antenna are equiva ent to much smaller capacity and resistance in the secondary circuit.

'ith the antenna polarity indicated for T,. Figure 1, adjacent turns of primary and secondary are at the same radio-frequency potential; so there is no dielectric field between primary and secondary, as there is in T, and T Hence, T, has less natural capacity than T and T which tends to compensate for the capacity added by the antenna. The three condensers bein alike, the three tuning dials represented in igure 1 will thus read nearly alike when all are adjusted to an one frequency. This greatly simplifies the process of tunin the receiver. The result just described, 1. e., that all tuning dials will read substantially alike when in proper adjustment for reception is, of course, dependent on the absence of regenerative action and contrasts with prior receivers employing tuned radio-frequency amplification without the elimination of undesirable coupling between stages, for in such receivers detuning of the amplifier output circuits was ordinarily necessary for the control of regeneration and oscillation, and, in any case, the tuning adjustment was dependent upon the regeneration present, and therefore upon the state of the batteries and of the vacuum tubes.

I claim:

1. A sharply selective, radio-frequency amplifying receiver comprising a triode having a grid, adplate and a cathode; means for applying ra io frequency waves across said id and cathode; a radio frequency trans ormer of the air core type compris' a primary coil of a few turns and a space secondary coil of more turns coupled to said primary coil so that substantially sha independent tuning of said seconds coi may be effected; a variable condenser for t said secondary coil; an amplifying source 0% direct current energy; circuit connections from said plate through said primary coil and said source to said cathode and from such terminal of said seconda coil to said cathode that coil terminals 0 unlike electro-magnetic polarit lead to said cathode; and a reverse feed back coupling substantially to neutralize the grid and plate feed back coupling associated with said triode comprising a limiting condenser of suitable low capacity, a tap-ofl' from a suitable potential po nt on said secondary coil to said imiting condenser and a connection to said grid from said limiting condenser.

2. The receiver as defined in claim 1 and further characterized by the following that a second similar triode has connections across its grid and cathode from the terminals of said secondary coil whereby said second triode is responsive substantially only to the wave energy transferred from said primary coil'to said secondary coil; a second similar air-core radio frequency transformer with its primary coil energized from the plate of said second triode v and said source of direct current energy; terminals of unlike olarity of the primary and secondary coi of said second transformer being connected to the cathode of said second triode; a second variable condenser connected across the terminals of the secondary coil of said second transformer for selective tunin substantial] secon reverse fee back coupling substantially to neutralize the grid and plate feedindependently; and a back coupling associated with said second triode comprising a limiting condenser of suitable low capacity, a tap-ofi from a suitable potential point on said secondary coil to said limiting condenser and a connection to the grid of said second triode from said limiting condenser.

3. In an amplifier, a vacuum tube provided with a grid,'a filament, and a plate, a grid circuit, a plate circuit, inherent capacity coupling between said grid circuit and said plate circuit, an output transformer associated with said plate circuit and having primary and secondary windings, atap on said-secondary winding, and a neutralizing capacity connected between said tap and said grid, said primary winding being placed in proximity to the portion of said secondary winding included between the tap and the low-potential end of said secondary winding, whereby natural capacity and dielectric loss due to the dielectric field between said primary and secondary windings are minimized.

4. In an amplifier, a vacuum tube provided with a grid, a filament and a plate, a grid circuit, a plate circuit, inherent capacity coupling between said grid circuit and said plate circuit, an output transformer associated with said plate circuit, said output transformer comprising a single-layer secondary coil having a tap and a, singlelayer primary coil placed in closed proximity to the turns (if said secondary coil included between the tap and the low-potential end of said secondary coil, whereby the coupling between the primary coil and said turns of the secondary coil is close, and a neutralizing capacity connected between said tap and said id.

5. In an ampli er, a vacuum tube provided with a filament, a grid and a plate, a grid circuit, a plate circuit, capacity coupling between said plate circuit and said grid circuit, an output transformer associated with said plate circuit, said output transformer comprising a single-layer seeondary coil provided with a ta and a singlelayer primary coil placed in c ose proximity to the turns of said secondary coil included between the "tap and the low-potential end of said secondary coil, a direct low-impedance path from the plate to one terminal of said primary coil, a direct low-impedance path from the other terminal of said primary coil to the filament, whereby the coupling between the plate circuit and said turns of the secondary coil is close, and a neutralizing capacity connected from said tap to said grid.

11 testimony whereof I aflix my signa ture.

LOUIS ALAN HAZELTINE.

back coupling associated with said second triode comprising a limiting condenser of suitable low capacity, a tap-off from a suitable potential point on said secondary coil to said limiting condenser and a. connection to the grid of said second triode from said limiting condenser.

3. In an amplifier, a vacuum tube provided with a grid, a filament, and a plate, a grid circuit, a plate circuit, inherent capacity coupling between said grid circuit and said plate circuit, an output transforn'ier associated with said plate circuit and having primary and secondary windings, a tap on said secondary winding, and a neutralizing capacity connected between said tap and said grid, said primary winding being placed in proximity to the portion of said secondary winding included between the tap and the low-potential end of said secondary winding, whereby natural capacity and dielectric loss due to the dielectric field between said primary and secondary windings are minimized.

4. In an amplifier, a Vacuum tube provided with a grid, a filament and a plate, a grid circuit, a plate circuit, inherent capacity coupling between said grid circuit and said plate circuit, an output transformer associated with said plate circuit, said output transformer comprising a single-layer secondary coil having a tap and a singlelayer primary coil placed in closed proximity to the turns of said secondary coil included between the tap and the low-potential end of said secondary coil, whereby the coupling between the primary coil and said turns of the secondary coil 18 close, and a neutralizing capacity said tap and said rid.

5. In an ampli er, a vacuum tube provided with a filament, a grid and a plate, a grid circuit, a plate circuit, capacity coupling between said plate circuit and said grid circuit, an output transformer associated with said plate circuit, said output transformer comprising a single-layer secondary coil provided with a tap and a singlelayer primary coil placed in close proximity to the turns of said secondary coil included between the tap and the low-potential end of said secondary coil, a direct low-impedance path from the plate to one terminal of said primary coil, a direct low-impedance path from the other terminal of said primary coil to the filament, whereby the coupling between the plate circuit and said turns of the secondary coil is close, and a neutralizing capacity connected from said tap to said grid.

In testimony whereof I aflix my signature.

rennet-ted between LOUIS ALAN HAZELTINE.

Certificate of Correction.

Patent No. 1,650,353.

Granted November 22, 1927, to

LOUIS ALAN HAZELTINE.

It is hereby certified that error a ppeals in the printed s ecification of the above numbered patent. reguirmgcorrection as follows: Page 4, lines 28 and 29, in the equation, at the beginning insert the factor 1 2; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 10th day of January, A. D. 1928.

M. J. MOORE, Actmg' Uommissioner of Patents.

Certificate of Correction. Patent No. 1,650,253. Granted November 22. 1927, m LOUIS ALAN HAZELTINE.

It; is hereby certified that error appears in the printedspeeificution of the above numbered patent; requiring correction as follows: Page 4, lines 28 and 29, in the equation, at the beginning insert the factor T22; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Ofhce.

Signed and sealed this 10th day of January, A. D. 1928.

[am] M. J. MOORE,

Acting Commissioner of Patents.

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