US2022478A - Volume control - Google Patents

Description

Nov. 26, 1935. H. o. PETERSON VOLUME CONTROL Filed Jan. 13, 1930 INVENTOR HAROLD o. PETERSON BY W M1 4, ATTORNEY Patented Nov. 26, 1935 VOLUME CQNTROL Harold 0. Peterson, itiverhead, N. 1 assignor to Radio Corporation of America, a. corporation'of Delaware Application January 13, 1930, Serial No..420,313:

2 Claims.

This invention relates to a volume controlled electrical system wherein it is desirable to maintain constant energy output from a variable energy input.

5; In volume control schemes as applied to radio receivers, collected signal energy, varying in in tensity, is split into two portions and separately rectified. One portion of the rectified energy is utilized for translation purposes and the other 101 for volume control so that the translation energy is maintained at a constant volume. A disadvantage of the system described resides in the fact that separate detectors are required, one for translation purposes and one for providing recti- 153 fied signal energy for volume control. An object of my present invention is to reduce the number of tubes required for volume control and I do this by utilizing one detector tube or electron discharge device for supplying rectified energy 203.5 for both translation and volume control. More specifically I accomplish this object by the use of a detector tube having an impedance associated with its output circuit. The detector rectifies the entire amount of collected or input en- 255 ergy; and, by virtue of the impedance referred to, potential differences are set up thereacross which are utilized for controlling the bias on a preceding electronic amplifier thereby volume controlling the system. The remaining portion of the energy appearing in the output circuit of the detector, rectifier or demodulator, is utilized for translation purposes.

Moreover, in known volume control systems, grid biasing potentials are applied to the recvtifier used for volume control, and the resultant anode current flow is utilized to vary the bias on the preceding radio frequency amplifier. In such a system with the input energy very weak, there is little fiow of plate current which, as

already indicated is to be used for increasing the amplification of the preceding amplifiers; and because of the small current flow, the system tends towards instability. A further object of the present invention is to provide a volume controlling system wherein a large current flow corresponds to a weak input and wherein the large current flow is utilized to control the amplification of the system. In this manner any tendency towards instability, for the reason mentioned, is effectively overcome.

Furthermore, in known systems, volume control is applied to only the radio frequency stages of a receiver. In order to improve sensitivity, a further object of this invention is to apply volume control to the intermediate frequency amplifier of a heterodyne system; and, to still further. ens hance volume controlling, it is a further object.

'of this invention to apply volume COIltIOl'lJObOth:

radio frequency and intermediate frequency amplifiers. 5.

If volume control biasing potentials are ap plied to the amplifiers instantaneously; that? is.- to say, with every minute and quick. change. in; intensity of the input energy, the tendency: of

the volume control arrangement would be to de- 10.

stroy the modulation of the incoming; energy.. To avoid such an effect is a further object of my invention and this I accomplish by inserting.

istic of my invention are defined with particu- 20;

larity in the appended claims. However, it may best be understood both as to its structural oreganization and method of operation by'referring; to the accompanying drawing in which Figure 1 shows my invention applied to: ax

simple radio receiving circuit,

Figure 2 illustrates.my invention applied to-:a heterodyne receiver; and

Figure 3 is given to aid in the explanation; of:

the operation of my invention, 30,:

Fig. 4 shows the circuit connections for the. automatic volume control. arrangement used: in. Fig. 2.

Referring to Figure 1, radiated signal energy collected upon antenna 2' is fed through tunable circuit t to the input side of an amplifier. comprising electron discharge device ii of suitable. type,here shown as a vacuum tube having a screen grid and indirectly heat-ed: cathodes Al:.

though only one amplifier stage has'been shown,.

for the sake. of simplicity, any suitable number; may be utilized. Amplified energy, from amplia fier 6: having a tunable circuit 8; in the output: circuit thereof, is fed to rectifying or demodulating apparatus Hl utilizing a single detector or rectifier it for rectifying or demodulating all of the collected signal energy. The output of detector I2 is fed to a suitable translating device such as phones It through, if desired, a suitable low frequency amplifier Iii of any well known 50 type. In order to utilize the same detector for volume controlling amplifier 6 as Well as for supplying translation currents to translating device l4, an impedance in the form of a resistance I8 is placed 55 in series with the output electrodes of rectifier 12. By means of a connection 20 between the output circuit of detector i2 and amplifier 5, the amplification thereof is varied inversely to the strength of the energy collected on antenna 2 and dir ctly as the unidirectional output current flow of the detector l2. In this manner, a single rectifier l 2, is utilized to provide both translation and volume controlling potentials.

In the ordinary type of detector utilized in the ordinary receiving circuit, the grid or control electrode thereof is biased negatively by a suitable potential source. However, if such a scheme were utilized in connection with detector l 2, with a weak incoming signal there would be a small current flow through resistance l8, resulting in unstable control of amplifier 5. Therefore, to provide a large current flow through resistance i8 when the incoming collected energy is weak, I bias the grid of tube !2 to a point such that in the presence of weak signals there is a large plate current fiow. Preferably I do this by the use of a blocking condenser 22 and a grid leak 24 rather than by biasing the grid 66 of the rectifier tube I2 positively. The relation of anode current to signal strength for the tube i2 is shown diagrammatically in Figure 3 where, for small signal values, plate current is a maximum. I have found that the use of large current flow to in crease amplification of the amplifier 6, materially improves stable action.

By virtue of the large unidirectional current flow through resistance I8 too large voltages may be applied to the grid of the amplifier tube 6. To

"preclude this possibility I insert in connection 20 a source of potential 255 opposed to the voltages produced across resistance 58. Voltage control may further be assisted by the use of variable tap 28 terminating connection 2%.

Biasing or control potentials applied to the radio frequency amplifier 5 need not necessarily be limited to the input or control electrodes thereof but may, by the suitable choice of elements such as resistance is and source of potential 26, be applied to the screen grid or anode thereof.

'Io smooth out the action of the volume con trolling apparatus and to make it unresponsive to sudden changes in volume caused, for example, by signal modulation of the collected high frequency energy, I associate with the volume control connection 2% a time delaying circuit comprising resistarice 3t and condenser 32. By suitable choice of values for resistance 38 and condenser 32, volume control action may be made as fast or as slow as desired.

My invention as applied to a heterodyne receiver is illustrated diagrammatically in Figure 2. Electromagnetic energy collected upon a suitable antenna 49 is amplified by radio frequency amplifier 22 of any desired number of stages. The amplified energy is fed into a modulator 44 together with locally generated energy generated by means of a generator 46. Beat frequency energy resulting from the modulation is fed into and amplified by an intermediate frequency amplifier 48, the output of which is detected or rectified by a suitable rectifier I ll similar to that shown in Figure l. The output of the detector l may then be amplified by amplifier 59 and translated by a suitable translating device 52.

For volume control, connections 29' and 299 similar to connection 2!] of Figure 1 are taken from detector Iii. As desired, volume control 10 biasing potentials may be applied to the control electrodes, screen grids oranodes of the amplifiers, and they may be obtained from separate resistances placed in the output circuit of detector ill or preferably from the same resistance using separate terminating taps for connections and zoo. Moreover, each connection 20, 200 may contain potential sources of the same or diiferent values as well as time delaying circuits similar to that shown in Figure 1. Fig. 4 shows 20 the latter connections. The connection 200 between the intermediate frequency amplifier and resistor 'l 8 includes the tap 28, voltage source 26', resistor 39' and condenser 32'. The detector l0 utilized in Figure 2 is preferably given, as described, the characteristic shown in Figure 3 whereby amplification of the amplifiers is varied in accordance with or directly as the unidirectional component appearing in the output circuit of the detector It; or, in other words, in- 80' versely to the strength of the signal collected upon antenna 40.

Having thus described my invention what I claim is:

1. In combination with the radio frequency 35 and intermediate frequency amplifiers of a superheterodyne receiver, a second detector of the leaky grid type, a biasing control path in the anode to cathode current path of the detector, and independent direct current connections sole- 1y from said biasing path to an amplification control electrode of each amplifier for regulating the gain of the amplifiers in a manner inversely proportional tothe receiver signal input variation, said connections being made to points of different potential of said biasing path.

2. In combination with the radio frequency and intermediate frequency amplifiers of a superheterodyne receiver, a second detector of the leaky gridtype, a biasing control path in the anode to cathode current path of the detector, and independent direct current connections solely from said biasing path to an amplification control electrode of each amplifier for regulating the gain of the amplifiers in a manner inversely proportional to the receiver signal input variation, said connections being made to points of different potential of said biasing path, and each connection containing a source of positive potential and a time delay network.

HAROLD O. PETERSON.

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