US1894578A - Method and apparatus for amplifying radiofrequency currents - Google Patents

Description

Jan. 17, 1933. J. M. AVERY 1,894,578

METHOD AND APPARATUS FOR AMPLIFYING RADIOFREQUENCY CURRENTS Filed July 13, 1925 2 Sheets-Sheet 2 A TTORNEY.

Patented Jan. 17, 1 933 UNETED S l A TES PATENT QFFEE JOHN IvI. AVERY, 03E FLUSHING, NEW YGRK, ASSIGNOR, BY MESNE ASSIGNMENTS, TO EAIJIO CGBEORATIGIJ OF AMERICA, is CORPORATION OF DELA'W'ARE IIIETHOD AND APYARATUS FOR .AIViPLZ A nlication filed Jul 13,

This invention relates to the amplification of radio frequency currents, such as, for eX ample, in radio telephone and telegraph sys tems.

In the operation of radio frequency amplifiers particularly at the higher frequencies, there is always present a tendency toward local oscillation in one or more of the ampli fier stages. Heretofore various attempts have been made to prevent such local and objectionable oscillations, but such attempts have usually resulted in either complication of de ices or dilficulty of adjustment, or if free from such local or objectionable oscillations, a uniform maximum transfer and amplification of energy at all the frequencies within its range was impossible. Variation in the amplifying power of the radio frequency amplifier also has not been satisfactorily accomplished heretofore by simple means.

An object of this invention is to provide an improved method and apparatus for sum plifying electric currents at radio frequencies, which will permit of uniform and maximum transfer of energy between said stages without oscillation in any of the same; and which will permit of a selective variation in the amplifying power of the system.

A further object is to provide an improved apparatus for accomplishing each and all of the above objects which will be relatively simple and inexpensive in construction; which may be operated, either with the same number of controls as already existing in similar sets, or with a minimum of additional controls; and with which amplification of the radio frequency currents may be obtained without distortion.

Various other objects and advantages will be apparent from the following description of several embodiments of the invention, and the novel features will be particularly pointed out hereinafter in connection with the ap pended claims.

In the accompanying drawings:

Fig. 1 is a circuit diagram illustrating a receiving circuit for a portion of a radio telephone and telegraph system and employing radio frequency amplification for the incom- FYING RADIOFREQUENCY CURRENTS 1925. Serial No. 43,103.

ing signals, the control of the amplification being in accordance with this invention;

Fig. 2 is a similar circuit diagram, with the exception that the thermionic relays are inductively coupled instead of being coupled by an impedance as in the preceding figure;

Fig. 3 is a diagram illustrating a circuit arrangement similar to Fig. 1 and including two stages of radio frequency amplification, with the amplifying power of the system controlled in accordance with the invention;

Fig. 4 is a similar diagram, but illustrating a modification of the invent-ion in the manner of controlling the amplifying power of the system;

Fig. 5 is another and similar diagram, but illustrating still another manner of controlling the amplifying power of the system; and

Fig. 6 is a circuit diagram of a portion of a radio telephone and telegraph receiving system employing two stages of radio frequency amplification, coupled by tuned impedance and with oscillations prevented in accordance wtih this invention, the system having but a single additional control for both stages of amplification.

Referring particularly to Fig. l in which is illustrated an application of the invention in simple form, the antenna 1 and its inductance 2 may be tuned by a suitable variable condenser 3, and grounded by a lead l. The antenna circuit is coupled or connected to a three-electrode thermionic valve or relay 5 in the usual or any suitable manner.

The relay 5 is coupled to a second and similar relay 6 by a tuned impedance, the con nections of which are as follows :The plate of the valve or relay 5 is connected by a wire 7 to one side of a preferably variable condenser 8, the other side of the condenser being connected by a wire 9 to one end of a grid inductance 10 which is tuned by a variable condenser 11, the inductance and condenser being connected to the filament circuit 12 by a conductor 13. The two condensers 8 and 11 may be separately operated, or coupled, in any suitable manner, for concomitant operation as shown in Fig. 1. One end of the inductance 10 is connected by a wire 14 to the grid of the relay 6.

The filament circuit is supplied with energy from a suitable energy source 15 in the usual manner, and a B or plate battery 16 is connected at one side to the filament circuit as usual in the art and at its other side by a wire 17 to the wire 7 leading to the plate of the relay An impedance 18, such as a resistor element or choke winding is in series in the conductor 17, so that the B or plate battery 16 may impress a continuous potential upon the plate of the relay 5. The impedance 18 holds back the radio frequency currents thereby forcing the latter to travel through the condenser 8 and the rest of the plate circuit. The B or plate battery 16 may be also employed as a source of energy for the output circuit of the relay 6. It will be understood that either the inductance 10 or capacity 11 may be made variable in order to obtain a prope tuning of the impedance coupling.

In the operation of the system of radio frequency amplification just described, the input currents entering the relay 5, either from a preceding relay or from the antenna circuit, will be amplified, and impressed upon the grid of the next successive relay 6. The battery 16 will 1 aintain a continuous potential upon the plates of the relays 5 and 6, the exact potei'itial being variable or not as desired. The impedance 18 prevents the passage of any material portion of the radio frequency currents directly through the battery and, therefore, such currents will pass through thevariable capacity 8 in the coupling of the relays. The condenser 8 is therefore in, effect in series with the plate circuit of the preceding relay.

For any given settingof the tuned impedance coupling between the relays, the capacity of the condenser 8 will be varied to such an extent as to permit of a maximum travel of energy between the relays without causing a condition of undesirable local oscillation of the relays, and by reason of the variableness of the condenser 8, this control of the transfer of energy without oscillation may be extended to cover all the wave lengths within the range of the receiving system. Therefore, during operation of the system, after the proper tuning of the coupling between the relays has been accomplished either by variations of the inductance 10 or tuning condenser 11 or both, the condenser 8 may be varied to control the amplification or transfer of energy between the relays so that the maximum energy transfer and amplification may be obtained without oscillation of the relays.

\Vhen a fixed value of inductance 10 and a variable capacity, are employed as the tuned impedance coupling, 1 find it of advantage to couple the condensers 8 and 11 for concomitant operation in any suitable manner, such as by placing them both on the same shaft or mechanically coupling them by other suitable mechanical means.

I have found that at the higher radio frequencies obtained through a decrease in the value of the effective capacity of the condenser 11, the value of the effective capacity of the condenser 8 should correspondingly decrease in order to prevent local oscillation of the relays. The practical value of condenser 8 will vary somewhat with the inductance to capacity ratio of the tuned impedance, with. the grid to plate capacity of the relays, and slightly with the other constants of the circuits. However, in general for the broadcast wave lengths now in use, I have found that if the condenser 11 has a maximum value of about .0005 microfarads then the condenser 8 should preferably have a capacity of approximately .0000? to .00005 inicrofarads as the maximum.

:lefcrri g to 2, the relays 5 and 6 are coupled by a tuned radio frequency transformer 19 in read of the tuned impedance of l, and the condenser Se corresponding to the condenser 8 of Fig. 1 is connected ln s with the primary winding of the transformer 19. The source of 15 or plate one. is also connected to the primary of the transformer 19, and also through an impedance 20 such as a esistor element to a wire or conductor 21 which connects the condenser cc to the plate of the relay 5.

In the operation of this particular system as shown .1 Fig. 2, the radio frequency currents from the plate circuit of the relay 5 will pass through. the condenser 8a and the 1 -iinary of the transformer 19, while a continuous potential will be impressed on the plate of the relay 5 direct from the battery or source of energy 16 through the impedance element 20. By varying the effective capacity of the condenser 8a the transfer of energy between the relays may be varied, so that the maximum transfer may be obtained without oscillation of the relays. If oscillation occurs in the amplifying system, itmay be eliminated by an adjustment of the corn denser 8a to decrease its effective capacity.

In Fig. 3 a detector relay is coupled to radio frequency amplifying relays 5 and G by any suitable means such as by either an impedance or transformer coupling, but in this particular instance, the tuning impedance coupling is illustrated as in Fig. 1. However, the source 23 of B or plate energy for supplying a continuous potential to the plates of the relays 5 and 6 is connected to the relay plates through impedance elements 241 and 25 which are connected by a common conductor :26 to the battery 23. In the conductor 26 1 preferably include a variable impedance 27 such as a resistor element. This resistor element 537 is shunted by a condenser 28 of relatively l rge value which smooths out the pulsations of current from the battery when several tubes are supplied with plate potential from one source of energy.

In the arrangement shown in Fig. 3, the degree of amplification of the radio frequency tubes may be varied by operation of the resistor element 27 which varies the potential impressed upon the plates of the radio frequency amplifying tubes. In case different relative potentials are desired for the plates of the two radio frequency amplifying tubes 5 and 6, the resistor elements 24 and 25 may be made variable although for ordinary purposes their value may be selected initially and remain unchanged. The resistor element 2? illustrates one manner of varying the potential transmitted from the battery 23 to the plates and is intended to be generic, it be ing understood that other equivalent means including battery taps or switches for varying the potential from the battery may be substituted within the principle and scope of the invention. The two condensers 8 which control the oscillations of the tubes 'may be either individually adjusted as shown in Fig. 3, or coupled for concomitant operation as by a common operating means as shown in Fig. 6 and described hereinafter.

In Fig. 4 a circuit arrangement similar to Fig. 3 is illustrated with the exception that the resistor elements 24 and 25 of Fig. 3 are replacedbycholrecoils24aand25a. Thechoke coils prevent the passage through the battery portion of the circuit of the radio frequency currents which are being amplified and transferred from relay to relay. The resistor element 2? in the plate circuits of the radio frequency amplifying tubes controls the plate potential therefor in the manner described in connection with the circuit shown in Fig. 3.

In Fig. 5 a circuit arrangement somewhat similar to Fig. 3 is illustrated in which the condenser 28 in the battery circuit is omitted, and a condenser 29 may be provided in series in the antenna circuit to further control the input circuit.

In Fig. 6 a somewhat similar diagram is also illustrated, but having all the condensers 8 coupled together for concomitant operation by means of a common operating handle or the like. The condensers 8, however, are electrically insulated from each other, but are simultaneously variable in order to simplify the number of controls required in the manipulation of the system. Preferably the common control or coupling means between the two condensers 8 should have provision for the adjustment of the condensers, relatively to one another, in order that they may be initially set to give the maximum amplification or transfer of energy, taking into account the constants of the particular plate circuits.

In receiving systems constructed in accordance with the invention, the incoming radio signals may be amplified at their original wave lengths by means of the relays, preferably of the thermionic tube or valve type, and with a maximum practically constant degree of amplification for all of the wave lengths within the tuning range of the amplifier, and without undesirable local oscillations, merely by the adjustment of the condensers 8 or 8a.

In referring to relays and thermionic valves, I intend to include devices having the functions specified, such as the well known three-electrode vacuum tube or audion and equivalents thereof.

In all of the circuits which have been described and illustrated, it will be understood that any number of radio frequency amplifying stages may be coupled by an obvious eX- pansion of the system, and that various changes in the details which have been herein described and illustrated in order to ex plain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

I claim 1. In a radio signaling system, a plurality of three-electrode thermionic relays, plate circuits and grid circuits associated therewith, an adjustable tuning means comprising a fixed inductance and a variable condenser cooperating with said grid circuit, an impedance associated with said plate circuit, and separated from said grid circuit, a variable condenser connected between said plate circuit and said grid circuit, and means comprising a mechanical connection between said tuning condenser and said variable con denser for causing the simultaneous actuation thereof, such that said variable con denser is reduced in value as said tuning condenser is adjusted for a higher oscillation frequency.

2. A radio receiving system comprising a plurality of three-electrode thermionic relays having plate and grid circuits, means comprising a coupling transformer associated between conjugate plate and grid circuits, means comprising av variable condenser for tuning the secondary of said coupling transformer, means comprising an impedance for the conveyance of direct current from said plate circuit, the primary of said coupling transformer being connected sub stantially in parallel with said impedance, and a. variable condenser connected in series with said primary for the adjustable controlling of the amount of radio frequency energy passed to said coupling transformer.

3. A radio receiving system comprising a plurality of three-electrode thermionic relays having plate and grid circuits, means comprising a coupling transformer associated between conjugate plate and grid circuits, means comprising a variable condenser for tuning the secondary of said coupling transformer, means comprising an impedance for the conveyance of direct current from said plate circuit, the primary of said coupling transformer being connected substantially in parallel with said impedance, 9. variable condenser connected in series with said primary for the adjustable controlling of the amount of radio frequency energy passed to said coupling transformer, and means comprising a mechanical connection between said tuning condenser and said variable condenser for reducing the effective value thereof when said coupling transformer secondary is tuned to a higher frequency.

4. A radio signalling system comprising in combination a first amplifier device having an anode, a cathode and a control electrode, a second amplifier, variable means to tune said first amplifier to a desired signal, variable means to couple said first amplifier to said second amplifier, said first mentioned means, said last mentioned means, said cathode and said anode being connected in series, and means for simultaneously varying said tuning means and said coupling means.

5. In a radio signalling system employing a plurality of amplifiers connected in cascade, means comprising a variablecondenser connected to one of said amplifiers of such a capacity range to tune the same to any desired frequency of a predetermined frequency range, and means to prevent said tube from going into oscillation, said means comprising a variable condenser having a range of smaller capacities than the capacities of said first named condenser for controlling the amount of energy transferred to said first mentioned amplifier from a preceding amplifier.

6. A tuned radio frequency amplifying system comprising means for coupling the plate circuit of one tube with the grid circuit of a succeeding tube and equalizing the transfer of energy between said circuits at all frequencies, said grid circuit having manual- 1y adjustable tuning means, said equalizing means comprising a manually adjustable condenser, and means whereby manual adjustment of said tuning means will automatically cause adjustment of said adjustable condenser to equalize the transfer of energy at all frequencies.

T. A tuned radio frequency amplifying system comprising means for coupling the plate circuit of one tube with the grid circuit of a succeeding tube and equalizing the transfer of energy between said circuits at all frequencies, said grid circuit having manually adjustable tuning means, and said equalizing means comprising a manually adjustable condenser, and means whereby manual adjustment of said tuning means will cause adjustment of said equalizing condenser to equalize the transfer of energy at all frequencies, the plate supply circuit being provided with a high impedance to restrict the escape of high frequency energy in the plate supply to thereby increase the effect of the high frequency energy on the equalizing condenser.

8. In a radio signalling system employing a plurality of space discharge amplifiers each thereof having grid circuits and anode circuits, a circuit including a tuning condenser in the grid circuit of one of said amplifiers and means for coupling the anode circuit of another of said amplifiers to said grid circuit comprising a condenser having a capacity of the order of one tenth the capacity of said tuning condenser.

9. In a radio signalling system employing a plurality of space discharge amplifiers each thereof having grid circuits and anode circuits, a circuit including an inductance and a variable tuning condenser in the grid circuit of one of said amplifiers, means for coupling the anode circuit of another of said amplifiers said grid circuit comprising a variable condenser having a capacity substantially smaller than said tuning condenser and a single means for simultaneously varying both said condensers.

i0. In a radio signalling system employing a plurality of space discharge devices eacn thereof having grid circuits and anode circuits. a circuit including a tuning condenser in the grid circuit of one of said devices for tuning said grid circuit to any one of a range of frequencies. and means for coupling the anode circuit of another of said devices to said grid circuit comprising a condenser whose capacity is of the order of magnitude of the capacity of said tuning condenser in the vicinity of the point where said tuning condenser is adjusted to tune said grid circuit to the highest frequency of said range of frequencies.

In witness whereof, I hereunto subscribe my signature.

JOHN M. AVERY.

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