US2037614A - Band pass amplifier coupling - Google Patents

Description

April 14, 1936. R BRADEN 2,037,61

BAND PASS AMPLIFIER COUPLING Filed Dec. 12, 1929 Z a Sheets-Sheet 1 1 19 I 1 7 1F fi 6 f 07 7 mum ATTORNEY -April 14; 1936. R BRADEN 2,037,614

' BAND PASS AMPLIFIER COUPLING Filed Dec. 12, 1929 5 sheets-sheet :5

' a l I' I I I l I I I I l 51 0 500 700 800 .900 /M //00 L 00 300 #00 AW M70 Flifll/iA/CY W KC- RENE A. BR DEN BY ATTORNEY Patented Apr. 14, 1936 UNITED STATES PATENT OFFICE BAND PASS AMPLIFIER COUPLING Rene A. Braden, New York, N. Y., assignor to Radio Corporation of America, a corporation of Delaware My present invention relates to amplifiers, and more particularly, to a band pass amplifier adapted to operate with a constant accepted band width.

In a co-pending application Serial No. 278,105 filed May 16, 1928, I have disclosed band pass amplifiers of the type comprising two or more circuits, each tuned to the mid-band frequency, and coupling means for the circuits arranged so as to produce a constant accepted band width. It was further shown, in the said application, that to produce this latter condition the coupling between the tuned circuits must vary as the circuits are tuned to various wave frequencies, the variation being such that the product of coupling and wave frequency is approximately constant. Coupling means of various types were, also, disclosed in the said application whereby the accepted band width was maintained at a constant value as the circuits were tuned to receive at various wave frequencies.

Now, I have discovered, by further experimentation, additional arrangements for coupling tuned circuits in a band pass amplifier of the type described in the above mentioned application.

In the new method two independent couplings are provided,'only one of these couplings being variable simultaneously with the tuning control, and being mechanically linked to the latter. Thus, as the circuits are tuned for various wave frequencies, the effective coupling is caused to vary in the proper manner to maintain constant accepted band width.

An object of the invention is to provide a method of maintaining constant accepted band width in a band pass amplifier which consists in providing two opposing couplings, and varying one coupling simultaneously with the tuning of the tuned circuits.

Still another object of the invention is to provide a band pass amplifier comprising a vacuum tube, a tuned circuit in the output circuit of the tube, a second vacuum tube, a tuned circuit in the input circuit of the second tube, capacitative coupling between the tuned circuits, inductive coupling reversed in phase with respect to the capacity coupling, means for varying either capacity or inductive coupling, or both, and means for causing the variable coupling or couplings to vary as the tuned circuits are adjusted to receive at various wave frequencies.

Other objects of ,the invention are to improve generally the simplicity and efiiciency of band pass amplifier coupling arrangements, and to provide devices of the latter type which are not only reliable in operation, but economical and simple to manufacture.

The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims, the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawings in which I have indicated diagrammatically several circuit organizations whereby my invention may be carried. into effect.

In the drawings:

Fig. 1 shows diagrammatically a novel type of coupling arrangement,

Figs. 2 to 5 inclusive show modified coupling arrangements embodying the present invention,

Figs. 6 and 7 are graphic representations of the coupling arrangements.

Referring, now, to the accompanying drawings, in which like characters of reference indicate the same elements in the different modifications, the numeral l indicates an electron discharge tube of either the three electrode or four electrode type, and shown preferably as the latter, the incoming signal energy to be amplified being impressed between the grid and cathode of the tube, and designated as input. The reference numerals 3 and 4 denote an inductance and condenser respectively thus forming the primary tuned circuit which is tuned to the midband frequency of the incoming signal.

The numerals 6 and I represent a condenser andinductance respectively, and form the secondary tuned circuit, which is also tuned to the mid-band frequency. The numeral 8 designates a second electron discharge device, preferably of the four electrode type, whose grid is connected to receive the voltage which is developed across the secondary circuit 6, 'l. The term output, in each modification, represents the circuit to which any subsequent circuits are connected to employ the amplified output of the device 8.

It is to be understood that the circuits embodying my invention are intended to select a definite band of frequencies from any part of a relatively wide range of frequencies. For example, a broadcast receiver embodying the invention would be capable of selecting and amplifying all signal currents contained within a band 10 kilocycles in width and would be able to select this 10 kilocycle band from any part of the frequency spectrum between 550 kilocycles and 1500 kilocycles. The mid-band frequency in this case is equal to the carrier wave frequency, and the accepted band extends equally on each side of the carrier frequency,

The novel method of a coupling as referred to heretofore is shown in Fig. 1, the primary tuned circuit 3, 4 being coupled to the secondary tuned circuit, 6, 1, l3, by mutual inductance of magnitude M, between the coils l3 and 3, and also by the condenser 19 of capacity C.

Either C or M must be varied to keep the band width constant, and it is intended that the coupling control be combined in any suitable manner with the tuning control. The advantage of this circuit is illustrated by the curves in Figs. 6 and 7.

Fig. 6 shows the coupling capacity C required for a constant band width of 10 kilocycles, when M/L has various values. (L is the inductance of coil 3, and of coils l and 13 in series.) The value of L assumed in calculating these curves was 253 microhenries. If the curve for M/L=0 is compared with that for M/L:.02, it will be seen that in the latter case the required range of adjustment of C is much smaller than in the former case.

Referring to Fig. 7 which shows the values of M required when G is constant, it is seen that the variation of M is much smaller when C=.50 mmf., than when C=0. It should be noted that the coil I3 must be connected so as to reverse the inductive coupling with respect to the condenser coupling, this being the condi tion described in co-pending application Serial No. 278,105, filed May 16, 1928 which causes the band width to remain almost constant. Then, only a relatively small variation of one of the two couplings is required to maintain absolute constancy of the band width.

In Fig. 2 is shown a modified circuit in which the coupling coil I3 is replaced by the link coupling coils 24 and 25 and the variable inductance 25 having an inductance L1. The inductance 26 controls the elfective inductive coupling, and otherwise the operation of the circuit is the same as that of Fig. 1.

Fig. 3 shows another modification in which the inductive coupling is controlled by movement of the coils 2d and 25 so as to vary the mutual inductances M1 and M2.

In Figs. 1, 2, and 3 I have not shown mechanical linking between the coupling adjustment and the tuning adjustment because in these three figures two alternative coupling adjustments are shown, e. g., in Fig. 1 either the coupling condenser !9 or the coupling coil 13 should be linked mechanically to the tuning control, but it is not intended that both of these shall be so linked.

Fig. 4 shows still another modification in which inductive coupling occurs in the form of mutual inductance of magnitude M between the coils 3 and l, and the capacity coupling is provided by the condenser 9, 50, H.

Fig. 4 shows a circuit employing a novel type of variable coupling condenser, one form of which has been described in my copending application, Serial No. 278,105, filed May 16th, 1928. In this circuit the coil 3 and the Variable condenser 4 constitute the primary circuit, the coil 1 and variable condenser G the secondary circuit, and the primary and secondary circuits are coupled by the electrostatic capacity between the plates 9 and H! which are attached to the high potential ends of the condensers 4 and 6, respectively. A metal plate I l is connected to ground (i. e. to the filament side of the circuit) and is mounted so that it can be slid between the plates 9 and 10 or drawn out. It must be insulated from the plates 9 and It and should move in a plane parallel to them and half way between. The capacity between 9 and I0 is reduced by the plate II, the amount of reduction being roughly proportional to the area of H which is between the plates 3 and i0. By this means the coupling capacity can be reduced from a comparatively large value almost to zero, and the ratio of maximum to minium capacity is much greater than can be secured with the conventional two-plate variable condenser of equal maximum capacity. Instead of being mounted as indicated in the drawings, the plate ll may be mounted so as to rotate on the shaft which carries the rotor plates of the variable condensers 5 and 6, and the plates 9 and 10 could then be conveniently attached to and supported by the stator units of the condensers 4 and 6.

A modification is shown in Fig. 5, in which the inductive coupling is directly between the coils 3 and l, and the. coupling condenser 19 is connected in series with coils 24 and 25, the latter being coupled inductively to coils 3 and 1, respectively.

In Figs. 1 to '7 inclusive combined inductive and capacitative couplings are utilized, the inductive coupling being reversed in phase with respect to the condensive coupling. That is, the

coupling network is arranged so that the voltage I induced in 'the secondary tuned circuit by the inductive coupling is opposite in direction to the voltage produced therein by the condensive coupling. Thus, at low wave frequencies, where the condensive coupling is ineffective, the inductive coupling provides sufficient coupling; whereas at higher wave frequencies, the inductive coupling is too large, but the condensive coup-ling becomes increasingly effective. As stated heretofore, this has been clearly described by me in my co -pending application Serial No. 278,105.

It is pointed out, however, that by utilizing the present invention consisting in varying one of the couplings at a predetermined rate with the tuning adjustment, the effective coupling between the coup-led tuned circuits is maintained such that the accepted band Width is kept absolutely constant throughout the tuning range of the coupled circuits. Figs. 6 and 7 clearly point out the rates at which the capacity coupling, or the inductive coupling, is to be varied in a combined capacitative-inductive coupling band pass network to achieve absolute constancy of accepted band width throughout the tuning range of the coupled circuits.

While I have indicated and described several systems for carrying my invention into effect it will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modifications in the circuit arrangements, as well as in the apparatus employed, may be made without departing from the scope of my invention as set forth in the appended claims.

What I claim is:

1. A band pass coupling network comprising two tuned circuits, combined capacitative and inductive couplings between the circuits, and means for varying at least one of said couplings simultaneously with tuning adjustments at a predetermined rate so as to maintain the accepted band width absolutely constant, throughout a frequency range of 550 to 1500 kilocycles, one of said couplings being reversed in phase with respect to the other.

2. A band pass amplifier coupling network comprising a pair of tuned circuits, combined capacitative and inductive couplings between the circuits, the couplings being so related that the voltages induced by them in the secondary tuned circuit are in opposite directions, and means including an adjustable reactance for varying at least one of said couplings simultaneously with tuning adjustments at a rate so as to maintain the accepted band width absolutely constant over the amplifier tuning range.

3. A band pass coupling network comprising at least two tuned circuits, combined capacitative and. inductive couplings between the circuits, the couplings being so related that the voltages induced by them in the secondary tuned circuit are in opposite directions, and means including an adjustable reactance common to the tuned circuits for varying at least one of said couplings simultaneously with tuning adjustments at a rate so as to maintain the accepted band width absolutely constant through a tuning range of 550 to 1500 kilocycles.

4. A band pass amplifier coupling network comprising at least two tuned circuits, combined capacitative and inductive couplings between the circuits, the couplings being so related that the voltages induced by them in the secondary tuned circuit are in opposite directions, and means including an adjustable condenser mechanically linked with the circuit tuning means for varying at least one of said couplings simultaneously with tuning adjustments at a rate so as to maintain the accepted band width absolutely constant throughout the amplifier tuning range.

5. A band pass amplifier coupling network comprising at least two tuned circuits, combined capacitative and inductive couplings between the circuits, said couplings being relatively reversed, and means including a link circuit having an adjustable reactance for varying at least one of said couplings simultaneously with tuning adjustments at a rate so as to maintain the accepted band width absolutely constant through the amplifier tuning range.

6. A band pass amplifier comprising a vacuum tube, 'a tuned circuit in the output circuit of the tube, a second vacuum tube, a tuned circuit in the input circuit of the second tube, capacity coupling between the tuned circuits, inductive coupling between the tuned circuits reversed in phase with respect to the capacity coupling, and means for causing one of said couplings to vary at a predetermined rate as the tuned circuits are adjusted to receive various wave frequencies, said rate of coupling variation being such that the accepted band width is maintained exactly constant throughout the tuning range of the amplifier.

'7. An amplifier adapted to operate through the broadcast range comprising a pair of oscillation circuits, an electron discharge tube having one of said circuits connected between its input electrodes, capacity coupling between the circuits, inductive coupling between the circuits reversed with respect to the capacity coupling, means for tuning said circuits to a desired frequency, and means including an adjustable grounded plate for vary ing said capacity coupling simultaneously with operation of the tuning means, at such a rate that said amplifier is uniformly selective through said range.

8. An amplifier adapted to operate over the broadcast range comprising a pair of oscillation circuits, ,an' electron discharge tube having one of said circuits connected between its input electrodes, capacity coupling between the high potential points of said circuits, inductive coupling between the circuits reversed in phase with respect to the capacity coupling, means for tuning said circuits to a desired frequency, and means for varying said inductive coupling simultaneously with operation of the tuning means at a rate such that the amplifier is uniformly selective over the said range.

9. An amplifier adapted to operate over the broadcast range comprising a pair of oscillation circuits, an electron discharge tube of the screen grid type having one of said circuits connedted between its input electrodes, capacity coupling between the circuits, inductive coupling between the circuits reversed in phase with respect to the capacity coupling, variable condensers for tuning said circuits to a desired frequency, and means for varying said inductive coupling simultaneously with operation of the tuning condensers at such a rate that said amplifier is uniformly selective through said range.

10. An amplifier adapted to operate'over the broadcast range comprising a pair of oscillation circuits, an electron discharge tube having one of said circuits connected between its input electrodes, capacity coupling between the circuits, inductive coupling between the circuits, the couplings being so related that the voltages induced by them in the secondary tuned circuit are in opposite directions, means for tuning said circuits to a desired frequency, and means for varying the inductive coupling simultaneously with operation of the tuning means at a rate such that the amplifier is uniformly selective over the said range.

11. An amplifier adapted to operate over the broadcast range comprising a pair of oscillation circuits, an electron discharge tube having one of said circuits connected between its input electrodes, capacity coupling between the circuits, a link circuit including inductive coupling between the circuits, the couplings being so related that the voltages induced by them in the secondary tuned circuit are in opposite directions, means for tuning said circuits to a desired frequency, and means for Varying one of said couplings simultaneously with operation of the tuning means at such a rate that said amplifier is uniformly selective over said range.

12. An amplifier operating over the broadcast range comprising a pair of oscillation circuits, an electron discharge tube having one of said circuits connected between its output electrodes, capacity coupling between the high potential points of said circuits, inductive coupling between the circuits reversed in phase with respect to the capacity coupling, variable condensers for tuning said circuits to a desired frequency, and means including an adjustable inductor for varying said inductive coupling simultaneously with operation of the tuning means at a predetermined rate such that the amplifier is uniformly selective over the said range.

13. A band pass amplifier comprising a pair of oscillation circuits, a screen grid tube having one of said circuits connected between its input electrodes, capacity coupling between the high potential points of said circuits, a link circuit including inductive coupling between the circuits, the inductive coupling being reversed in phase with respect to the capacity coupling, means for tuning said circuits to a desired mid-band frequency of the broadcast range, and a single means for varying one of said couplings simultaneously with operation of the tuning means at such a rate that the accepted band width is exactly constant throughout said range.

14. The method of transferring electrical energy having a predetermined frequency band width throughout a predetermined range of frequencies from an exciting circuit to a tunable absorbing circuit, which consists of transferring the energy both electromagnetically and electrostatically in separate paths, and causing said electromagnetic transfer to vary at such a rate as said absorbing circuit is tuned through said range that said band width is maintained absolutely constant throughout said range.

15. The method of transferring electrical energy having a band width of ten kilocycles through a range of frequencies between 550 and 1500 kilocycles from an exciting circuit to an absorbing circuit, which consists of transferring energy both electromagnetically and electrostatically in separate paths, adjusting said absorbing circuit for resonance with desired current frequencies in said exciting circuit, and adjusting the rate of variation of the electromagnetic energy transfer as said absorbing circuit is adjusted through said frequency range to maintain said band width ten kilocycles wide throughout said frequency range.

16. An electrical system comprising an exciting circuit and a tunable absorbing circuit, an electrostatic coupling between said circuits adapted to decrease in a predetermined way with increase of frequency as said absorbing circuit is tuned, and an electromagnetic coupling between said circuits so related to the first coupling as to transfer energy to the absorbing circuit reversed in phase with respect to the energy transferred by said electrostatic coupling, and additional means for varying said electromagnetic coupling simultaneously with tuning of said absorbing circuit, the rate of variation of said electromagnetic coupling being so chosen as to render said absorbing circuit uniformly selective throughout its tuning range.

1'7. The method of transferring electrical energy having a predetermined frequency band width throughout a range of frequencies from an exciting circuit to a tunable absorbing circuit, which consists of transferring the energy both electromagnetically and electrostatically in separate paths, and causing said electromagnetic energy transfer to vary as said absorbing circuit is tuned in such sense as to maintain said band width absolutely constant throughout said range of frequencies.

18. An electrical system comprising an exciting circuit and a tunable absorbing circuit, an electrostatic coupling between said circuits, an electromagnetic coupling between said circuits, said couplings being so poled that their combined energy transfer remains approximately constant with frequency as said absorbing circuit is variably tuned through a predetermined frequency range, and additional means, simultaneously operative with the tuning of the absorbing circuit, for adjusting the electromagnetic coupling to maintain the combined energy transfer absolutely constant throughout said frequency range.

19. A band pass amplifier coupling network comprising a pair of tuned circuits, combined capacitative and inductive couplings between the circuits, the couplings being so related that the voltages induced by them in the secondary tuned circuit are in opposite directions, and means including an adjustable reactance for varying at least one of said couplings simultaneously with tuning adjustments at a predetermined rate whereby a precisely determined band width is transmitted over the amplifier tuning range.

20. A band pass amplifier comprising a vacuum tube, a tuned circuit in the output circuit of the tube, a second vacuum tube, a tuned circuit in the input circuit of the second tube, capacity coupling between the tuned circuits, inductive coupling between the tuned circuits reversed in phase with respect to the capacity coupling, and means for causing one of said couplings to vary at a predetermined rate as the tuned circuits are adjusted to receive various wave frequencies, said rate of coupling variation being such that a precisely determined band width is transmitted throughout the tuning range of the amplifier.

21. An amplifier adapted to operate over an extended tuning range comprising a pair of oscillation circuits, an electron discharge tube having one of said circuits connected between its input electrodes, capacity coupling between the circuits, inductive coupling between the circuits reversed in phase with respect to the capacity coupling, variable condensers for tuning said circuits to a desired frequency, and means for varying said inductive coupling simultaneously with operation of the tuning condensers at such a rate that said amplifier is uniformly selective through said range, said variable inductive coupling attaining a minimum value at some point within said tuning range.

22. An amplifier adapted to operate over an extended tuning range comprising a pair of oscillation circuits, an electron discharge tube having one of said circuits connected between its input electrodes, capacity coupling between the circuits, inductive coupling between the circuits reversed in phase with respect to the capacity coupling, variable condensers for tuning said circuits to a desired frequency, and means for varying said capacity coupling simultaneously with operation of the tuning condensers at such a rate that said amplifier is uniformly selective through said range, said variable capacity coupling attaining a maximum value at some point within said tuning range.

RENE A. BRADEN.

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