Automatic Volume Control Research Articles

Automatic Tuning, Simplified Circuits, and Design Practice

The principles underlying automatic frequency control of the oscillator in superheterodyne receivers have been outlined in previous papers given before the Institute of Radio Engineers. This paper deals with simplification and improvements in operation of frequency control circuits and their application to automatic (electronic) tuning control. A new type of "discriminator" which differentiates between mis-tuned signals on the high-frequency side of resonance and those on the low-frequency side is described and its operation demonstrated by means of a visual frequency indicator. The operation of the discriminator is such that it may be used to supply audio-frequency components corresponding to the amplitude modulations of the received carrier wave and automatic volume control potentials as well as the control voltage for the frequency control circuits. This multifunction is described and illustrated. Alternative circuit connections to improve the compromise between discriminator sensitivity, audio fidelity, and selectivity are explained and illustrated. The use of vacuum tubes in such manner that they act as reactive components and the manner in which their apparent reactive impedance may be controlled by varying the tube parameters is demonstrated. The action of a complete receiver embodying automatic (electronic) tuning control in overcoming mis-tuning and oscillator frequency drift will be demonstrated.

Testing Broadcasting Receivers

AT an informal meeting of the Wireless Section of the Institution of Electrical Engineers held in November 1935, Dr. R. L. Smith-Rose opened a discussion on the methods of examining the performance of wireless sets used for the reception of broadcasting. No specification was then available of the standards of performance at which it was desirable to aim in the production of such receivers. Quite recently, however, the Radio Manufacturers Association has published a “Specification for Testing and Expressing Overall Performance of Radio Receivers”, and a discussion on this specification was opened by Mr. Stuart Hill at a meeting of the Wireless Section of the Institution of Electrical Engineers held on February 3. The above specification is in two parts, dealing respectively with electrical and acoustic tests. The first part describes laboratory methods of measuring the sensitivity and selectivity of a receiver, and also its susceptibility to noise and the performance of its automatic volume control. The second part describes the corresponding methods of measuring frequency response, acoustic sensitivity, hum and acoustic output. In each case the proposed methods of expressing the results are described and illustrated by means of typical graphs included in the specification.

A Direct-Reading Pitch Recorder and Its Applications to Music and Speech

An electrical arrangement was devised, by means of which rapid variations in pitch with time, such as occur in music or speech, could be directly recorded even in detail. The arrangement consisted of amplifiers, a wave form adjuster, an automatic volume control, and a frequency meter. The frequency meter itself is essentially the same as the two‐tube thyratron inverter, which was first described by Hull as one of the applications of thyratron, and recently modified by Hunt. Efforts were made to utilize the frequency meter in conjunction with the wave form adjuster and the automatic volume control in order to make it suitable for indicating the rapid pitch variations, accompanied by large intensity variations, in music as well as in speech. The final indication of pitch is made in logarithmic scale, several applications of the arrangement to music and speech being given.

Considerations in the design of a high-fidelity radio-gramophone

Receiver performance has in the past been limited by inadequate audio-frequency range (50–5000 cycles per sec.) and inadequate range of volume levels. The paper describes a radio-gramophone in which alternative upper frequencylimits of 3, 5, 7, and 8 kilocycles per sec. are provided, and the range of volume levels is increased by including a form of “negative automatic volume control” in the audio-frequency amplifier.The first section of the paper summarizes the requirements of the new radio-gramophone, which include radio-frequency, intermediate-frequency, and audio-frequency circuits each of adjustable band width. The radio-frequency section includes amplified automatic volume control and a selective quiet tuning and indicating circuit. For gramophone reproduction a new pick-up and needle, with a cut-off frequency of 8000 cycles per sec, are described, together with a motor giving extreme constancy of speed. For the final acoustic reproduction, an improved electrodynamic loud-speaker is described having a paper cone with a metallic centre portion to give good reproduction up to 8000 cycles per sec.Circuit diagrams and performance characteristics of the individual sections of the receiver are illustrated, and the paper concludes with a series of acoustic frequency-response curves taken under various conditions.

A New Tube for Use in Superheterodyne Frequency Conversion Systems

The major disadvantage of existing methods of frequency mixing is found in high-frequency operation with comparatively low intermediate frequencies, where serious coupling exists between oscillator and signal circuits in spite of, electrostatic screening. Suppressor modulation of a radio-frequency pentode largely overcomes many of the defects but the oscillator voltage required is large and the low plate resistance limits the gain. For these reasons, a new tube has been developed (designated the 6L7) wherein the above disadvantages are largely overcome. The new tube contains five grids: the first grid is a remote cutoff signal grid, the second and fourth are screens, the third is used as the modulator grid controlled by a separate oscillator tube, and the fifth grid is a suppressor. The ideal characteristics of such a tube are derived. The actual characteristics of the tube developed are shown and a brief discussion of the results obtained is given. A discussion of the flow of electron current to a negative grid due to an unusual transit-time effect at high frequencies is given and it is shown that operation with sufficient grid bias reduces the phenomenon. The characteristics of this tube also make it particularly suitable for use as a radio-frequency amplifier in receivers where the available automatic volume control or detector voltage is low; in this case the automatic volume control voltage is applied to both No. 1 and No. 3 grids.

Considerations in the design of a high-fidelity radiogramophone

Receiver performance has in the past been limited by inadequate audio-frequency range (50–5 000 cycles per sec.) and inadequate range of volume levels. The paper describes a radio-gramophone in which alternative upper frequency-limits of 3, 5, 7, and 8 kilocycles per sec. are provided, and the range of volume levels is increased by including a form of “negative automatic volume control” in the audio-frequency amplifier.The first section of the paper summarizes the requirements of the new radio-gramophone, which include radio-frequency, intermediate-frequency, and audio-frequency circuits each of adjustable and width. The radio-frequency section includes amplified automatic volume control and a selective quiet tuning and indicating circuit. For gramophone reproduction a new pick-up and needle, with a cut-off frequency of 8 000 cycles per sec., are described, together with a motor giving extreme constancy of speed. For the final acoustic reproduction, an improved electrodynamic loud-speaker is described having a paper cone with a metallic centre portion to give good reproduction up to 8 000 cycles per sec.Circuit diagrams and performance characteristics of the individual sections of the receiver are illustrated, and the paper concludes with a series of acoustic frequency-response curves taken under various conditions.

Aircraft Radio Equipment for Use on European Air Lines

The apparatus to be described has been developed to provide a transmitting and receiving equipment for small and medium commercial and private aircraft which will be extremely simple to operate and as foolproof as possible. Many features are introduced which, although they have been in use for broadcast and other commercial radio apparatus, have not been applied to aircraft radio equipments. For example, an electrical remote tuning system is used for the receiver, and automatic volume control on both telephony and telegraphy is provided. The equipment provides a telephonic range of 180-200 miles, and a telegraphic range of 350-400 miles, and weighs only sixty pounds complete.

Recent Developments in Power Line Carrier

Some recent developments in power line carrier telephone equipment that greatly enhance the value of this type of communication are described in this paper. Two outstanding developments have been an automatic volume control, and means for interconnecting the carrier circuits with 2-wire telephone facilities. In addition, much has been achieved in lowering installation and maintenance costs, and in improving reliability of operation.

Recent developments in power line carrier

Some recent developments in power line carrier telephone equipment that greatly enhance the value of this type of communication are described in this paper. Two outstanding developments have been an automatic volume control, and means for interconnecting the carrier circuits with 2-wire telephone facilities. In addition, much has been achieved in lowering installation and maintenance costs, and in improving reliability of operation.

Diode Detection Analysis

This paper gives the current and output relations for the linear and square-law diode detector in terms of the detection efficiency and the detector and load resistances. The square-law case is shown to yield results similar to the linear for large input potentials and reasonable values of load. Employing the rectification-current-input-voltage characteristic, the graphical method is used to show that serious distortion is developed for deep modulation whenever an appreciable audio load is shunted across the diode resistor. It is found that M = 1 + D(A-1), where M is the modulation ratio at which cut-off begins, D the detection efficiency, and A the ratio of the audio impedance to the direct-current value of the diode load. The value of M is shown for various load conditions in both the linear and square-law cases. The paper shows that the use of a small condenser across the load decreases the detection efficiency but increases the input impedance. The connection to the driving circuit of a second diode for the development of automatic volume control potential is shown to cause distortion when such a tube is used with a delay bias. Mention is made of the importance of considering the impedance of the driving circuit, and attention is called to the failure of any of the methods of analysis to consider all of the factors involved.

Compulsory tuning in relation to a.v.c.

Automatic volume control in its simplest forms suffers from several defects. The principal difficulties are discussed here and a method of overcoming the troubles is described

Copper-Oxide Rectifier Used for Radio Detection and Automatic Volume Control

A new type of radio detector has been developed which depends for its action on the rectifying properties of the boundary between copper and cuprous oxide formed on the copper at a high temperature. In order to make the copper-oxide rectifier useful up to broadcast frequencies, it was necessary to use small disks and a high current density. The high current density was obtained in part by connecting an inductance in parallel with the rectifier and tuning it with the rectifier capacity. The circuits developed possess unique advantages in that harmonic distortion is practically eliminated, a stage of audio-frequency amplification is eliminated, and automatic volume control of variable , μ tubes as well as other tubes is achieved without the necessity of using an auxiliary tube for volume control. A newform of automatic volume control made possible by the use of a single rectifier element as an asymmetrical resistance is described and discussed.

Automatic volume control for aircraft radio receivers

Automatic volume control for aircraft radio receivers

Wide Range Scales for Fading Records by Electrical Means

The electrical means discussed in the following paper are two in number. Relatively small modifications of the response characteristics of the recording system may be obtained by the use of a combination of plate detection and grid detection in which the latter becomes active only for strong signals. Great modifications of the response characteristics are produced by circuit arrangements of the type used for "automatic volume control." Curves are given showing typical results. These show the possibility of obtaining greatly increased scale ranges and also of obtaining scales in which the recorder response is roughly proportional to the logarithm of the strength of the carrier wave. The response to side bands is stated to be small.

A Broadcast Receiver for Use in Automobiles

The purpose of this paper is to present several important features affecting the design of a broadcast receiver for use in automobiles. The design of the receiver is carried along step by step with special reference to (1) type of collector, (2) ignition shielding, (3) electrical characteristics of receiver, (4) physical structure of receiver, (5) power supply. From measurements made on an experimental receiver installed in an automobile the ignition interference is found to be greatest at the higher frequencies in the tuning range. Observations made during a road test of the receiver indicate a normal service range of from 50 to 100 miles on such stations as WJZ, WOR, and WEAF. The severe fluctuation of the signal encountered in travel through hilly country indicates the desirability of some form of automatic volume control.

Recent Developments in Superheterodyne Receivers

Major electrical elements of a modern superheterodyne receiver-tuned radio-frequency amplifier, intermediate frequency amplifier detector and audio-frequency amplifier-are briefly discussed in light of recent developments. A practical automatic volume control is described. Curves illustrating the major performance characteristics of the receiver are shown.

Automatic Volume Control for Radio Receiving Sets

A receiving set is described in which the radio-frequency amplification is automatically controlled to give a nearly constant radio-frequency voltage at the detector, independent of differences in antenna signal voltage. This results in nearly uniform response at the loud-speaker from nearby and distant broadcasting stations and also reduces the effect of fading. The method employed consists in using the rectified carrier voltage to adjust the grid bias of the radio-frequency amplifier tubes. There are indicated the solutions of special problems that arise in carrying out this method.