US1692257A

US1692257A - Wave signaling system

Info

Publication number: US1692257A
Application number: US229912A
Authority: US
Inventors: Louis A Hazeltine
Original assignee: Hazeltine Corp
Current assignee: BAE Systems Aerospace Inc
Priority date: 1925-02-27
Filing date: 1927-10-31
Publication date: 1928-11-20
Anticipated expiration: 1945-11-20
Also published as: US1869894A; GB253146A; US1649589A; USRE17530E; US1650353A; FR598968A; DE514965C

Description

L. A. HAZELTINE WAVE SIGNALING SYSTEM Original Filed Feb. 27, 1925 louis/1H Awww INVENTQR azeZ m e f BY ATTORNEYS APatented Nov. 20, 1928.

,UNITED STATES PATENT. yoFFici-i.

LOUIS A. HAZELTINE, 0F HOBOKEN, NEW JERSEY, ASSIGNOR TO HAZELTINE COR- PORATION, A CORPORATION OF DELAWARE.

WAVE SIGNALING SYSTEM.

Original application filed/February 27, 1925, Serial `No 12,000Patent No. 1,648,808, and in Canada May 4, 1925. Divided and this application filed October 31, 1927. Serial No. 229,912.

This ,invention relates to wave signaling systems, particularly radio receiving systems employing tuned radio-frequency amplification, and has for its object the provision of means for securing substantially complete neutralization of the capacity coupling in vacuum tubes under certain circumstances.

In my United States Letters Patent No. 1,533,858, granted April 14, 1925, there are described means for eliminating coupling between stages kof an amplifier including the neutralization of the capacity coupling between the grid and plate electrodes of a vaclium tube and between the apparatus connected thereto. Such neutralization is accomplished, briefiy, by the use of an auxiliary coil and a neutralizing condenser connected in series between the grid and the filament system, the neutralizing coil being coupled to a primary coil connected between the plate and the yfilament system.

In general for com-plete neutralization the coupling between the auxiliary coil and the primary coil should be so close as to behave practically like perfect coupling-that, is, with a coupling coeflicient equall to unity. Now circumstances sometimes arise in which thecoupling by choice or necessity is looser, no longer behaving like perfect coupling and so resulting inN incomplete neutralization. For example, at relatively low frequencies itmay be desired to employ coils having their turns bunclied or wound -in spiderweb form or mounted on individual supporting structures, resulting in each case in a .physical separation of the coils. Again,` at very high frequencies the reactances of the leads become appreciable even lwhen the leads are made as short as feasible, thus also loosening the coupling between the circuits of Ythe coils. In accordance with this invention it has been found that substantially complete neutralization may be attained at all frequencies within frequency amplifying transforme-r the coils of which are arranged in accordance. with this invention and suited for use in a low radiofrequency amplifier such as represented in ydetector tube D, are then amplified at the pulse frequency by A1 and A2 again, on the reflex principle, and are finallylamplified and supplied to the relay by the vacuum tube A,.. These and other details are more fully described in m copending application for United States ette-rs Patent No. 12,000, filed /February 27, 1925, issued November 8, 1927,

present A y as Patent No. 1,648,808, of which this application is adivision.

Interstage radio-frequency couplings are minimized by thevuse of individual metal compartments for each stage and 'bythe use of series resistances Rp, Rg, or impedance Lpd, and shunt capacities Cp, Gg, Cp., Cpd and Ca,

in the leads, and especiall by the neutralization mea-ns involving coi s L Lm, LS1, and condenser C, in one stage, and coils L2,'L2, L52, and condenser (32 in the other stage.

The use for which the receiver of Fig. 1 is intendedinvolves relatively low radio frequencies, where the single-layer type of secondary winding (commonly used in broadcast receivers) is preferably replaced by a multilayer coil Ls and where the primary coil L, and auxiliary coil Ln' may be of the pancake form, placed close together, as represented in Fig. 2, where Ln, Lp, L, indicate either Lm, Lm', LS1, or LM, Lpg, Ls2 of Fig. l. With this arrangement, as previously mentioned, it is difficult to secure the exceedingly close coupling between lLrl and Lp which is desired. It hasbeen found, however, that if thecouplingcoeiicient between Ln and the secondary'coil LS-is lequal to the product of the coupling coeiiicienty between Ln and Lp, and the.

coupling coefficient between Lp and Ls, then the coeflicient of coupling between Ln and Lp need not be substantially unity. This result maybe attained with Lpplaced between Lnand ment of the respective vacuum tube A, or

A2 being neutralized (allowing the filaments of the other vacuum tubes to remain lighted), to tune in a strong signal, and then to adjust the neutralizing capacity until the signal d1s appears. With close coupling between L., and Lp, the relation then existing would be C@ Nn -gf (l) where Cgp is the grid-plate coupling capacity,

Cn is the neutralizing capacity and Nn and Np l are the numbers of turns of coils Ln and Lp, respectively, all for the stage being neutralized. If the coupling is not very close, the above procedure will result in the existence of the following more generalrelation,

where Lns is the mutual inductance between Ln and LS, and Lps'is the mutual inductance between Lp and Ls. Relation (2.) of course, reduces-to relation (l) for very close coupling, from the formula for mutual inductance, which for LnB and Lp, would have identical factors except Nn and Np, respectively.

Now when the filament is lighted, there will flow, in'addition to the currents previously present, the amplified plate current. This current Hows through coil Llp and gives rise to a self-induced voltage, in that coil proportional to the self-inductance Lp, and to y'a voltage in coil Ln proportional `to/the mutual inductance Lm, between Ln and Lp. If a balance is still to be maintained, it is necessary that these voltages produce Vequal (and, of course, opposite) additional-currents through C@ and Cn. Since the currents are proportional to the capacities, the latter must be inversely proportional to the respective voltages. Hence -QLD- Ln CII- Lvl I Combining this relation with (2),

Now the coefficient of coupling k between two coils is defined as the quotient of the mutual Lesage? inductance by the square rootof the product of the self-inductances. Substituting this relation for each mutual inductance in (4) we have 7cns'V LnLs: knp'JLnl- Jp 7c,1/LL Lp which at once reduces to the relation stated above enf/apa.. (6)

the conditionA (6), showing the advantage mentioned above of making the coupling between Ln and L,D as close to unity as feasible.

The above derivation does not consider the voltages induced in the leakage self-inductances of Ln and Lp due to the capacity currents flowing through them. However, the consideration of capacity current in Lp leads to exactly the same result as above, since the derivation will apply to any current in Lp. The only error in neutralization that remains is thus that due to the capacity current in the leakage reactance of Ln, this error manifesting itself by a slight theoretical unbalance .at frequencies differing from that at which Cny is adjusted. Since the capacity associated with Ln, consisting of natural capacity plus C, is ordinarily very small, and the leakage self-inductance is kept; as small as feasible by fairly close coupling, this error can be shown to be ordinarily quite insignificant. The relations (2) and (6) therefore give substantially complete neutralization under all practical conditions.

A suitable experimental procedure lfor atplete neutralization is as follows: The filament of the vacuum tube to be neutralized is turned out and al strong signal is. impressed between its grid and filament. The neutrali'zing capacity Cn and the coil couplings are then adjusted until no signal voltage appears between the plate and the filament, both when the output circuit is tuned and when it is not. The absence of signal voltage can conveniently be ascertained by a zero reading on a vacuuming tube voltmeter connected between the plate and filament system of the vacuum tube being neutralized. l

This invention is applicable to any amplifier in which the secondary coil is connected in a closed alternating-current. circuit, whether tuned or not. If the circuit isvnot tuned, the procedure described in the preceding paragraph is modified simply by obtaining a balance with at least two different impedance conditions in the secondary circuit, as for example, open circuit and short circuit.

I claim:

l. In an electric circuit arrangement for neutralizing capacity coupling between the grid and plate circuits of a vacuum tube, including a primary coil connected between the plate and the filament system, a secondary coil, andan auxiliary coil and a neutralizing capacity connected in series between the grid and the filament system, the auxiliary and primary coils being utilized under such circumstances that substantially unity coefficient of coupling between their circuits is not present, the method of securing substantially complete neutralization, which comprises arranging said coils so that the ratio of the mutual inductance between the secondary coil and the auxiliary coil to the mutual inductance between the secondary coil and the primary coil is equal to the ratio of the mutual. inductance between the auxiliary coil and the primary coil to the self-inductance of the primary coil and so that said ratios are also equal to the ratio of the coupling capacity to the neutralizing capacity.

2. In an electric circuit arrangement for neutralizing capacity coupling between the grid and plate circuits of a vacuum tube, including a. primary coil connected between the plate and the filament system, a secondary coil, and an auxiliary coil and a neutralizing capacity connected in series between the grid and the filament system, the auxiliary and primary coils being utilized under such circumstances that substantially unity coeiiicient of coupling between their circuits is not present, the method of securing substantially complete neutralization, irrespective of the currents flowing through the primary and secondary coils, which includes the ste of interposing the primary coil physically etween the other two coils in such manner that the cocoil, and an auxiliary coil and a neutralizing` capacity connected in series between the grid and the filament system, the auxiliary and primary coils being utilized under such circumstances that substantially unity coefficient of coupling between their circuits is not present, the method of securing approximately complete neutralization, irrespective of the currents flowing through the primary and secondary coils, which includes the step of interposing the primary coil physically between the other two coils in such manner that the coefficient of coupling between said other two l coils is less than the coefficient of coupling between the primary and either of the other coils.

4. In an electric circuit arrangement for neutralizing capacity coupling between the grid and plate circuits of a vacuum tube, having a grid, a. plate, and a filament system, the combination of a secondary coil, an auxiliary coil, and a primary coil physically interposed between said secondary and auxiliary coils, whereby the coefficient of coupling between said secondary and auxiliar coils is less than the coeliicient of coupling etween said primary and either of the other coils said primary coil being connected between the plate and the filament system, said auxiliary coil being connected in series with a neutralizing Acapacity between the grid and said filament system, and said secondary coil being connected in a closed alternating-current circuit.

In testimony whereof- I affix my signature.

LOUIS A. HAZELTINE.