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Difficulties associated with swept-gain (ie, time-varied gain) as a means of controlling sensitivity in ultrasonic scanning are considered. Automatic sensitivity control as a possible technique for determining sensitivity is discussed. A simple automatic sensitivity control in the form of automatic gain control (AGC) was constructed and applied in scanning complex tissue structures. It is concluded that automatic sensitivity control allows acceptable ultrasonic images to be produced and involves the operator in little manipulation of controls.

An analog-digital hybrid decoder which combines amplitude and duration threshold detection and bipolar violation sensing capabilities for decoding bipolar signals is described. The main features of the decoder are: 1) a preamplifier with automatic gain control (AGC), 2) amplitude and duration threshold detectors, 3) a bipolar violation sensor, and 4) a unipolar pulse generator. The decoder is extremely robust and is self-synchronizing. If, during operation, burst errors occur, introducing bipolar violations in the received signal, the decoder decides that, where a violation has occurred, a binary "0" was transmitted. If, for some reason, the decoder is perturbed from its synchronous condition, it requires at most 1-b duration to reacquire synchronization. That is, the decoded message contains at most one erroneous bit.

Because of the space requirements, poor tracking capabilities, and connection difficulties of four-ganged potentiometers for use in quadraphonic volume controls, many manufacturers of four channel equipment have been reluctant to use a single master volume control. Instead they have tended to use pairs of dual controls, typically connected as front and back gain controls combined with a pair of left/right balance controls. This results in even poorer tracking and in virtually unrepeatable balance setting for any room arrangement other than an ideally symmetric one where the listener is located on the axis requiring equal level settings on both gain controls. This paper discusses a four channel monolithic volume control whose gain is set by a single dc control voltage, with the ease of connection and space savings this implies. In addition to good channel to channel tracking, it has a fully flexible set of dc controlled balance functions and the capability of gain variation with logic enhanced 4-2-4 matrix recording systems. 1

A seismic trace recorded with suitable gain control can be treated as a stationary time series. Each trace, χ j ( t ), from a set of traces, can be broken down into two stationary components: a signal sequence, α j ( t ) * s ( t —τ j ), which correlates from trace to trace, and an incoherent noise sequence, n j ( t ), which does not correlate from trace to trace. The model for a seismic trace used in this paper is thus χ j ( t ) =α j ( t ) * s( t —τ j ) n j ( t ) where the signal wavelet α j ( t ), the lag (moveout) of the signal τ j , and the noise sequence n j ( t ) can vary in any manner from trace to trace. Given this model, a method for estimating the power spectra of the signal and incoherent noise components on each trace is presented. The method requires the calculation of the multiple coherence function γ j ( f ) of each trace. γ j ( f ) is the fraction of the power on traced at frequency f that can be predicted in a least-square error sense from all other traces. It is related to the signal-to-noise power ratio ρ j ( f ) by where K j ( f ) can be computed and is in general close to 1.0. The theory leading to this relation is given in an Appendix. Particular attention is paid to the statistical distributions of all estimated quantities. The statistical behaviour of cross-spectral and coherence estimates is complicated by the presence of bias as well as random deviations. Straightforward methods for removing this bias and setting up confidence limits, based on the principle of maximum likelihood and the Goodman distribution for the sample multiple coherence, are described. Actual field records differ from the assumed model mainly in having more than one correctable component, components other than the required sequence of reflections being lumped together as correlated noise. When more than one correlatable component is present, the estimate for the signal power spectrum obtained by the multiple coherence method is approximately the sum of the power spectra of the correlatable components. A further practical drawback to estimating spectra from seismic data is the limited number of degrees of freedom available. Usually at least one second of stationary data on each trace is needed to estimate the signal spectrum with an accuracy of about 10%. Examples using synthetic data are presented to illustrate the method.

An automatic gain control circuit has been described in the paper, allowing stabilization of a radiation spectrum exhibiting no photopeak. Its operating principle is based on comparison of the count rate above two discrimination levels. One of them is usually selected near the upper end of the radiation spectrum where the relative slope of the integral curve is high, the other one where the relative slope is low. The AGC described can also be used for stabilization of a radiation spectrum exhibiting a photopeak.

An IF amplifier that provides a temperature insensitive Q (adjustable independently of center frequency) of 50 at a center frequency of f/SUB 0/ of 1 MHz, over a 100/spl deg/C temperature range is presented. The design also features supply independent biasing, input and output buffering, a 40-dB (automatic gain control) range and a center frequency voltage gain of up to 60 dB. Results obtained from computer simulations, discrete, and integrated prototypes are compared.

The exact input-output relationship is derived for a firstorder automatic gain control loop wherein the variable gain is an exponential function of the gain control voltage. The exact solution is compared to the linearized solution, and the condition for valid linearization is given.

A systematic work has been done in designing and fabricating a complete remote control guidance system, using FM-AM, for a flying vehicle. This paper deals with the selection of the proper channel following the guidance receiver on the vehicle, the necessary amplification of the command signal on that channel and the final servo stage.The channel discriminator consists of two selective amplifiers using twin-T in the feedback loops, followed by a differential amplifier. The frequency sensitive output is fed to a high current gain control amplifier with actuator coils as the loads. The complete circuit, its working, printed board layout and the results obtained are discussed.

A microphone amplifier is described which possesses good noise characteristics at all gain settings and the capability of handling large input signals without appreciable distortion at low gain settings. A single potentiometer is used as the gain control to 1) vary the negative feedback to provide high overload capability at low gain, and 2) attenuate the output to provide a minimum gain of zero. The circuit is developed from a two-transistor building block.

1. The proposed method permits the comparison of the frequencies of generators having an identical nominal value and a submultiple ratio of nominal values of frequency. 2. Since the circuits shown do not contain resonant or phase-splitting circuits tuned to a specific frequency, they can be used over a wide frequency range without readjustment. 3. Use of a limiter at the input of the signal zero-crossing detector and a comparison circuit using tunnel diodes has afforded a dynamic range of amplitudes of input signals from 0.5 to 20 V, which is especially convenient in the comparison of the frequency of a test generator having a frequency obtained from radio receivers not having automatic gain control. 4. The errors in comparing frequencies by means of a flip-flop as the phase detector and with the aid of a recording of the oscillations of the difference frequency on the stripchart of a recording instrument are approximately the same as for the oscillographic method of comparing frequencies by means of a circular sweep with a modulating spot that is 1/100 the length of the periphery. 5. Recording of the indications on a stripchart eliminates continuous participation of an operator in counting the number of oscillations, which is convenient during long-term or round-the-clock comparison of the frequencies of generators. 6. Stencils and recording instruments the pointers of which move perpendicularly to the longitudinal axis of the stripchart over the entire width permit a rapid orientational evaluation of the difference frequencies from the recording being made.

The relation between input and output of many linear systems and circuits is ordinarily found by repeated use of functional inversion, i.e., the process where, given \bar{y} = Z\bar{x} one finds \bar{x} = (1 /Z)\bar{y} . Many nonlinear circuits and systems can be analyzed using functional inversion in exactly the same way. The methods for accomplishing this inversion however are different. Where the nonlinear relations are given as graphs, the inverse relations are shown by the same graphs. Where derivatives and integrals are involved, approximate inverses can be obtained using a generalization of the "reversion" method of Sims [11] and Pipes [12], or the iteration method. Practical examples given include the design of a nonlinear equalizer and the analysis of a feedback circuit, a tunnel diode network, and an automatic gain control circuit. The mathematical bases of the methods are discussed, along with their representation by flow graphs, and the insertion of initial conditions.

Short hop radio systems of the type described in this issue require broadband intermediate frequency amplifiers in the range of a few hundred MHz which have a large gain control range and stable characteristics with respect to temperature; they must also make efficient use of bias power and have well behaved noise properties. This paper describes the design of such amplifiers. We give extensive measurements for an amplifier with a 1 dB bandwidth of 120 MHz centered at 300 MHz and an automatic gain control range of 43 dB.

This paper describes a five-transistor automobile receiver designed to use newly developed RCA drift transistors. These drift transistors, which inherently have a high maximum available gain and low feedback capacitance, provide good performance with a minimum number of stages, thus contributing to low over-all circuit cost.

The design and performance of a versatile automatic recording spectrofluorometer are described. The instrument has a modular design and is capable of measuring fluorescence excitation and emission spectra, polarization of fluorescence, and phosphorescence spectra, each as a function of temperature and pH. Both right angle and frontal illumination may be used. A split beam optical system combined with an automatic gain control (AGC) amplifier assures long term stability and freedom from the effects of light source fluctuations. Corrected emission spectra in energy units are obtained automatically by the use of an adjustable function generator (Vernistat). A quantum counter used in conjunction with a second function generator and the AGC amplifier permits recording of true excitation spectra.

Investigation was conducted on the evaluation of various solid-state devices with particular emphasis on signal-handling capability (cross-modulation performance) and the circuit techniques for filtering the interfering signals for VHF TV tuners. From this investigation, some clear requirements are ascertained as to the selection of the solid-state devices and to the circuitry for the VHF TV tuners. On the basis of these requirements, a high performance solid-state tuner was developed whose performance surpasses that of tube equipped tuners in all respects except gain.

Two super-regenerative oscillators for an NQR spectrometer have been built covering the frequency range from 250 up to 1100 MHz. The two oscillators of microstrip type use 1/4 lambda or 1/2 lambda resonators, possess sideband suppression and automatic gain control and allow insertion of a finger dewar for low temperature investigations. A series of nitrogen-iodine charge-transfer compounds have been studied.

Sandia Laboratory is developing and testing prototype equipment to continuously record outputs from three short-period and three long-period unattended seismometers for up to 120 days. Timing accuracy will be within 0.1 second throughout the record period. The system will be capable of recording a 70 decibel signal range. As much as 42 decibel attenuation can also be applied to each short-period data channel by an automatic gain control system to compensate for high levels of background noise. Concurrent with the development of the recording system, a playback system is being developed and tested which will convert the recorded data and timing signals to the standard Vela Uniform tape format. According to present schedules, the systems should be fully evaluated in the laboratory and in the field by the beginning of 1967.

An electronic monitoring system has been developed to detect the four conditions that usually lead to fibrillation in the infarcted heart. Artifact-free QRS detection is accomplished by passing the preamplified QRS through a bandpass filter, an automatic gain control (AGC)circuit, a full-wave rectifier, a nonlinear amplifier, and positive and negative slope detectors. High-threshold logic circuitry then applies the timing criteria necessary for positive identification of a QRS complex. A printout of the ECG is made if 1) the number of premature beats in the last minute exceeds a physician-set number (0 through 10), 2) the number of successive anomalous beats (i. e., area increase, QRS increase, or polarity reversal) exceeds a physician-set number (0 through 5), 3) an "early" premature beat occurs (i.e., R-R' < QT), or 4) a multiformal beat is detected (i.e., its morphology differs from that of the previous anomalous beat).

An intermediate-frequency amplifier, providing double-tuned response using single-tuned circuits with negative feedback, is described. Particular attention is centered on the problems arising in the case where relatively narrow pass bands are wanted.

Impulse noise interference, such as may be caused by sparking electric motors or automobile ignition systems, can interfere with the performance of a television receiver in the following principal ways: First, the impulses appear directly in the picture; second, the synchronization separator input circuit may charge up to such an extent that the picture loses synchronization; third, the impulses may provide false information to the AGC system thereby causing a sharp reduction receiver gain. Of the three, the latter two effects are by far the more serious. Consequently, noise ``suicide'' or noise inverter circuits, for the protection of the sync separator and AGC circuits have been widely used.

Measurements on 4-terminal double-diffused field-effect transistors show considerable dissimilarity in the control characteristics of each gate, which can only be explained on the basis of a nonuniform channel doping. By using a linear approximation to the actual form of the channel doping, a theory of these devices in the pinchoff region is developed and compared with experimental observations. For the devices used, the agreement is extremely good in that it accurately predicts the ratios of the two transconductances and their variation with voltage. It is observed that the transconductance of the more heavily doped gate (gate 1) exhibits a nearly linear variation with voltage applied to the other gate and that the linearity is maintained over a wide range of gate 1 voltages. Such a property could be usefully exploited in automatic gain control systems.

A simple automatic control system capable of compensating for detector gain changes over a dynamic range of 10 has been developed for laboratory and aerospace radiation detection systems. The basic concept involves a feedback system that adjusts the system gain to keep the peak of a stable calibration source at a predetermined level. Two variations are described, one providing continuous calibration and the other calibrating on command. The effects of calibration source characteristics and critical circuit parameters on the total system accuracy are discussed. Typical results for a proportional counter X-ray spectrometer indicate that the system gain can be maintained to within 4 percent of its initial value for a detector gain degradation of a factor of 3.

Outputs of a Gray code counter are used to synthesize digital Walsh functions that are free from hazards. This method, which produces sequency-ordered Walsh functions, also uses a binary code to select the order.

Similar considerations govern the age circuit design of both tube and transistor television receivers.

Adaptive ferroelectric devices utilizing piezoelectric (PE)-ferroelectric (FE) interact~ons ate reviewed. These devices are typ~cally composed of two ceramic FE capacltors mechanically bonded together. When an input voltage 1s applled to one capacitor. it vibrates due to its PE properties. The vibrations are coupled to the output capacitor where a PE voltage is developed. Because of thc PE-FE interaction the PE coefficients of the capacitors depend on their state of FE polarization. Thus, the output voltage of the device can be ‘set’ to different values by the application of a polarizing voltage adapt pulse to either of its capacitors. Electronic control systems requiring analog memory for ‘setting’ a variable or function to a desired level have generally been limited to ones employing mechanical memory devices. Solid-state systems are possible using adaptive devices. One such system is described which supplies a ‘settable’ control voltage in the range 0 to + IO Vdc that can be remembered accurately for periods of time measured in years. yet can be changed quickly (milliseconds) or slowly (dekaseconds) merely by applying a polarizing voltage adapt pulse. Positive or negative pulses reduce or increase the control voltage setting, respectively. The system can be used for analog control of electronic functions provided appropriate automatic gain control circuits are employed.

The engineering of a data system for use on the switched message network is reviewed. First, the conditions imposed by this specific application are shown to influence the selection of signal characteristics, and the choice of raised-cosine pulse shaping is given support by a brief treatment of some pulse transmission fundamentals. Finally, the results of a field trial are summarized to show that, while the system objectives were met, factors such as delay distortion, attenuation distortion, and transmission loss limited the performance obtained.

Narrow band and broad band cold cathode discharge tubes have been developed for control of microwave power in the 3 cm band. Constructional details and operational data are discussed. Reference is made to the use of such devices in automatic gain control circuits and to the application of speech modulation of microwaves.

In order for the human retina to achieve its very wide operating range (one billion to one in light intensity), high accuracy of spectral discrimination (the eye can distinguish among at least 10 million different shades of object color), constancy of object color, and uniform field of color perception, it appears necessary that the retinal receptors incorporate the following feedback-control processes: time-average feedback, spatial-average feedback, and automatic gain control. Time-average feedback would adapt each receptor to the time-average light it receives; spatial-average feedback would modify the signal from each receptor as a function of a weighted spatial-average of the receptor signals throughout the retina; and automatic gain control would keep the sensitivity of each receptor constant regardless of the adaptation conditions. This paper presents a model of a retinal receptor which incorporates these feedback control processes, and which appears to be consistent with physiological and psychological evidence.

Radar angle tracking noise, such as that due to angular and amplitude scintillation of the target echo, is increased by the response of the receiver agc (automatic gain control) to the low frequency components of the fading of the echo envelope. An increase in angle tracking noise spectral density by a factor of two to three is representative of what can happen when the radar echo envelope is approximately Rayleigh distributed. This phenomenon has been investigated by analog simulation of the agc, both for an ordinary linear filter in the feedback path and for a nonlinear filter with quick attack and slow release in the loop. Since the increase in tracking noise decreases monotonically with increasing agc time constant, an analysis is presented to describe a particular basic problem which requires the agc time constant to be kept short, namely, the transient rise in average signal strength encountered by a radar when closing rapidly on a target. In fixing the agc time constant, a compromise must be reached between increase in tracking noise and the transient increase in mean output signal strength. Whatever considerations motivate a particular choice of agc time constant, the effect of the agc on angle noise spectral density can be determined from the curves presented. The results obtained show that the use of the nonlinear filter with quick attack and slow release does actually produce the desired result of reducing the transient rise in output signal strength while keeping the increase in noise spectral density constant.

Previous work on optimum gain control is extended to an important class of diversity receivers used for digital data transmission through fading media and for radar. As in the single diversity case the optimum gain (which yields minimum average cost of receiver saturation) is extremely insensitive to relative costs of saturation at the upper and lower dynamic range bounds. The sensitivity to relative cost decreases as the order of diversity increases. Optimum gain and performance characteristics are given from which dynamic range requirements for diversity receivers can be deduced.

Methods of automatically positioning tuned circuits for rapid frequency changes are discussed. Equipment ranging from low level single-sideband exciter-receivers to high power linear rf amplifiers are considered with attention given to the correlation of positioning accuracy, tuning change time, and ultimate cost of equipment. The merits and limitations of mechanical positioning, follow-up potentiometer servo systems, and phase servo systems, are noted. Special emphasis is placed upon the adjustment of tank circuits in linear power amplifiers. The problem of obtaining phase information for the servo systems is presented and several improved circuits for tuning and loading detection are explained. The paper is concluded with a general discussion of gain control, sequencing of control circuits, and protection of tubes during tuning cycles.

In the equipment described, group delay is measured by means of a carrier which is frequency modulated with a signal at 1 Mc/s. The change of phase delay of the demodulated signal relative to the original 1 Mc/s signal, before and after the insertion of the network in the signal path, is the group delay of the network under test. The systematic accuracy of the method is considered in relation to the accuracy required for measuring waveguide networks suitable for use in microwave multi-channel telephony links.A superheterodyne system is employed in the equipment with an intermediate frequency of 70 Mc/s. For measurements on a display basis the signal- and local-oscillator frequencies are mechanically varied in synchronism to give a constant intermediate frequency. Automatic gain control is provided in the i.f. amplifier so that networks with losses up to 20dB can be measured; limiters reduce the effect of amplitude modulation produced by networks having a large attenuaion/frequency slope. The phase stability of the equipment is ensured by the use of a feedback amplifier in the 1 Mc/s path. A phase comparator of the modulator type is used in which errors due to the variation of the input level have been reduced.An accuracy of ±0.1 ns is obtained for point-by-point measurements on networks such as filters. Group-delay/frequency characteristics over a band 40 Mc/s wide may be displayed on an oscilloscope with an accuracy of about ±0.2 ns.

The fine guidance sensor designed for the Princeton Experiment Package of the Orbiting Astronomical Observatory is described. The sensor is capable of providing two axis error signals over a field of view of 4 arc min and with an accuracy of 0.1 arc sec. The sensor uses the light-gathering capability of the experiment's primary optical system and also has its own optical system and electronics system for signal processing. The optical system and electronics block diagram are discussed in detail. Transfer characteristics are described for each axis. The signal-to-noise ratio of the sensor is derived and presented for various star intensities. The effect of several stars in the field of view is described. The redundancy configuration is described, and the predicted reliability is discussed.

A synthesis procedure is developed for a dominant third-order system (as opposed to the usual dominant second-order system) where the size of the complex closed-loop pole region is not specifically restricted but is contained within a circular boundary. The plant considered is of third order, with a real pole at the origin and a pair of complex poles with negative real parts. The added real pole affords an additional degree of freedom with which to meet the system-time domain specifications. The compensation prescribed is a biquadratic network with complex zeros, and compensation poles are constrained to exhibit only second-order effects. The procedure is based on the association of the desired closed-loop pole parameter values with open-loop parameter values in the ( \Omega^{2},\Sigma ) plane, which is in actuality the natural-frequency-squared damping-constant plane. A constant gain factor is assumed, but this constraint may be removed if a tandem gain control system is employed. This assures that the gain variations are much slower than the system response. Relations between the desired nominal closed-loop poles and the plant region and compensation locations are derived for a prescribed circular closed-loop pole region. The nominal plant pole location is a design specification, while the allowable plant region depends on the closed-loop pole location and region, i.e., a change in size of one region is reflected as a proportional change in size of the plant closed-loop pole region. The remote compensation pole location is primarily determined by minimizing transient distortion while ensuring a specified degree of stability.