US2124211A - Combined amplification and tuning controls - Google Patents

Description

COMBINED AMPLIFICATION AND TUNING CONTROLS Filed Oct. 17, 1934 7Q J//V/IZ M INVENTOR ATTORNEY Patented July 19, 1938 UNITED STATES 1 2,124,211 COMBINED AMPLIFICATION AND TUNING CONTROLS Walter van B. Roberts, Princeton, N. J., as'signor to Radio Corporation of America, a'corporation v of Delaware Application October 17, 1934, SerialNo. 748,610

- 1 claim; (01. 179 -171) My present invention relates to uni-controlled connection with the drawing in which I have in-,

tuning and amplification control adjustments for radio receivers, and more particularly to novel and improved devices for'correlatingpthe tuning and radio frequency energy transfer characteristics of the selector networks of radio receivers.

One of the main objects of my present invention is to provide capacity coupled radio frequency amplifiers wherein the'capacity coupling exists betweena following tunable radio, frequency selector network and a' preceding non-tunable plate circuit of a radio frequency amplifier; the energy transfer characteristic and the tuning characteristic of the coupled circuits being varied in such a manner, and by such devices, that a predetermined transfer characteristic over the entire tuning rangeis secured with the capacity coupling as small as possible at' the high frequency end of the tuning range, and as" large as convenient at the low frequency end.

Another important object of the invention is to provide an adjustable capacity device between ,v selector circuit of a radio frequency amplifier, the

tunable circuit being arranged for coupling to the untuned plate circuit of a preceding amplifier, the tuning condenser being providedwith.

The novel features which I believe to be char acteristic of my invention are set forth in particularity in the appended claim, 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 dicated diagrammatically several circuit organizations whereby my invention may be cariedinto effect.

In the drawing:-

Fig. 2 shows the circuit diagram of the amplifier embodying one mechanical form of a come, 1

bined tuning and amplification control'device.

Referring now to the accompanying drawing, wherein like reference characters in the dif' ferent figures designate similar circuit elements,

the radio frequency amplifier of Fig. 1 shows a pair ofscreen grid tubes I and 6 capacitatively coupled by a condenser C. The input electrodes, of amplifier tube 1 may be considered arranged for coupling to any source of signal energy. For example, the amplifier network of Fig. l'may be considered as the radio frequency amplifier of a superheterodyne receiver. In such case the .output electrodes of tube 6 may be adapted for connection to the first detector of the set, or the tube 6 may itself be the first detector Of course, the signal collector. may, in that case, be connected to the input electrodes of amplifier l, and a tunable selector circuit may be connected to the input of amplifier I. a l

If the amplifier network is in areceiyer of the tuned radio frequency type, then the amplifier I- may be the first tunable radio frequency amplifier, and the tube 6 may be the'secondtunable radio frequency amplifier, or it may be the dey tector. be understood as havinga wide applicability; whatever the nature of the circuits which are coupled, the problem to be solved by the present invention is tovary the tuning and radio fre-' quency energy transfer characteristics of the coupling network so as to obtain a desired energy transfer characteristic over the tuning range of the receiver.

The plate of amplifier l is connected to the low potential side of the usual grid biasing network 2' through a path which includes the radio frequency choke 3 and the source of plate voltage 4. The frequency selection network comprises the coil 5,and the variable tuning condenser t connect:

, ed in shunt with the coil 5; the tunable circuit be ing connected in series between the input grid ofv tube 6 and the low potential'side of the grid biasing network I. The coupling condenser C connects the plate side of choke 3 to the high alternating voltage side of the following tunable cir-- cuit. The problem presented for solution by the In any case the present invention istoinvention of the present application is to vary the tuning of the tunable input circuit of tube 6 over the tuning range of the receiver, and yet maintain a desired and predetermined radio frequency energy transfer through the coupling condenser C over the entire tuning range of variable condenser t.

Fig. 1 shows the manner of securing such a relationship, or rather such a correlation of tuning and energy transfer, and it is also accomplished in a simple, effective and economical manner. An auxiliary condenser S is connected across the plate circuit of tube I, and in shunt with condensers C and t. The magnitudes of condensers S and C are so chosen, and their rates of variation are uni-controlled with the variation of condenser t in such a manner, that a predetermined energy transfer characteristic can be secured. Such a characteristic may be of the uniform, or flat, gain type; that is to say, the amplification of the signal energy will be substantially uniform over the tuning range of the receiver embodying the amplifier network shown in Fig. 1.

To preserve as large a tuning range as possible, say over the broadcast band which is between 500 and 1500 kilocycles, the value of condenser C should be as small as possible at the high frequency end of the tuning range of the receiver; it should be as large as convenient at the low frequency end. It is not believed necessary for the purposes of the present application to present the theoretical considerations which support the premise that for a given set of other conditions, the value of condenser C required for a given amplification depends upon the value of condenser S; It will be sufficient to point out that such a premise is established in an analysis entitled Maximum Amplification In Capacity-Coupled Circuits, appearing on page 20 of Electronics for July, 1931.

It can now be stated that it is the purpose of the present invention to vary the capacity value of condenser S in such a fashion that for a desired amplification characteristic the condenser C will be required to assume a small value at the high frequency end of the tuning range and a relatively large value at the lower frequency end. In Fig. 1 the dotted lines U designate the mechanical uni-control arrangement for varying the three condensers. This mechanical variation of the condensers should, of course, be accomplished in an economical, effective and simple manner, and

without the use of sliding contacts or pigtail connections.

In Fig. 2 such a mechanical construction is shown. The normal condenser construction is this purpose, and the shaft 9 will be understood as additionally being connected to, and supporting on it, the rotors of the tuning condensers of other amplifier stages. and I3 may be used in conjunction with each tuning condenser of each stage. For the purpose ofsimplicity, however, the construction between a given pair of amplifier tubes is only considered. It will also be understood that it is un- The auxiliary plates l4" necessary to show the side view of the condenser plates, or the housing construction of the plates because those skilled in the art are fully aware of the manner of constructing such condensers of the variable type.

The profile of the plates of condenser S are cut to give any desired variation of condenser S with respect to the variation of tuning condenser t. The two condenser assemblies S and t are located far enough apart on the shaft so that the stray capacity between stators is smaller than the smallestvalue of coupling capacity desired at C. The disposition of a grounded shield 8 between the adjacent stators l3 and I2 will reduce the required separation, but the separation should not be reduced too much, or the minimum capacity of condensers S and t will be increased too much by the close proximity of their stators to the grounded shield 8.

The variable capacity C consists of the metal conductor composed of two plates l6, l6 metallically connected together by a bolt l5. This conductor is insulated from shaft 9, although mechanically adjustable therewith. A block of insulation material l0, such as a collar of insulation material, is carried by the shaft 9, and the bolt I5 is disposed within the collar.

The collar I0 is rigidly connected to shaft 9 so that adjustment of shaft 9 results in movement of plates 16, lfi' with rotors l4 and H. Plate I6 is disposed adjacent the end stator'l2 of condenser 15, while plate i6 is disposed adjacent the end stator I3 of condenser S. The plates l6 and Hi cooperate with their adjacent stator plates to provide the condenser C. Hence it will be seen that as'shaft 9 is varied the capacity values of condensers S, C and t are varied. The conductor comprising plates l6 and I6 is not electrically connected to any portion of the circuit, but serves to vary the effective separation between the stadenser S to the high alternating potential side of the tunable circuit of amplifier 6. The value of this inter-stator capacity is varied by the plates It and I6, and the disposition of these plates between the adjacent end stators is varied at a rate dependent upon the rate of variation of the capacities of condensers S and t. It is not believed necessary to go into any further detail concerning specific profiles for the blades of the condensers, since such profiles can be easily determined by those skilled in the art when it has been decided what the amplification characteristic is to be; As stated before a specific type of such characteristic is one that is uniform over the receiver tuning range, and in Fig. 2 it is to be understood that the capacity values of condensers S and C are varied with the variation of condenser t so that the transfer of radio frequency energy to the output circuit of tube 6 is substantially uniform over the tuning range of the receiver. It will now be appreciated that this relation of amplification and tuning has been secured in a highly economical and simple fashion,and without sliding contacts.

For a further disclosure of the manner of constructing a variable condenser of the type shown in Fig. 2, reference is made to application Serial No. 387,148 of J. L. Bonanno, filed August 20, 1929,

issued as Patent No. 2,040,426 o'nMay 12, 1936, wherein there is claimed, as well as disclosed, the

type of variable condenser shown in Fig. 2, and

network; in the present application the variable condenser construction of the Bonanno patent is used to secure a predetermined amplification characteristic over the tuning range of the receiver. r 7

While I have indicated and described several systems for carrying myinvention into efiect, it will be apparent to one skilled in the art that my invention is by nomeans limited to the particular organizations shown and described, but that many modifications may be made without departing from the scope of my invention, as set forth in the appended claim.

What I claim is: V

In combination in a high frequency network which comprises a first tube having an untuned plate circuit which includes a radio frequency choke and a shunt capacity, a second tube provided with a tunable circuit, a condenser coupling the plate circuit of the first tube to the tunable circuit, and means including a common control for simultaneously varying the value of said shunt capacity, coupling condenser and the tun-

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