Audio-frequency Power Research Articles

Microwave Modulated Scatter Active Array Distortion Sidelobes

A signal processing antenna consisting of an array of modulated scatter elements is described. Time-modulation of array elements for radiation pattern and sidelobe control was initially described more than a half-century ago. Recent decades have produced many advances and extensive documentation for both transmit and receive arrays with time modulated elements. The new article presented here includes both receive and transmit functions in an array of modulated scattering elements. This new approach to time-modulated array experiments greatly simplifies both the physical array elements and the measurement apparatus. An incoming continuous wave (CW) signal in space arrives at the array, is time-modulated by the elements, and then re-radiated in space. The only electrical connections to the individual array elements are low-frequency time-modulation signals. The measurement apparatus consists of a spectrally pure and frequency stable CW source, an audio sine wave modulator with different phases for each element, a microwave receives down-converter to a baseband IF from dc to 24 kHz, and an audio frequency power spectrum analyzer running on a laptop computer. Models that incorporate both the CW signal arrival angle and radiation angles for each modulation and distortion product are presented, along with measurements of 16 element arrays in the anechoic chamber at 2.3 GHz using time-modulation frequencies near 1 kHz. The individual array element time-modulators are nearly ideal RF switches, and the agreement between the new time-modulated scatter array models and measurements is remarkable.

Experimental study and sterilizing application of atmospheric pressure plasmas

The atmospheric pressure surface barrier discharge (APSBD) in air has been used in killing Escherichia coli. We have developed two similar dielectric barrier discharge (DBD) structure types of nonthermal plasma jets (PJ) driven by 5–20 kHz audio-frequency power at atmospheric pressure. At a flow rate of 200 L/h (argon), a stable, arc-free discharge was produced. At 1.5 cm from the nozzle, the gas temperature was kept at 47 °C for PJ-1 source and 38 °C for PJ-2 source. Some research on sterilization has been carried out and results show that such a plasma jet source as PJ-2 is very effective in the disruption of E. coli.

Audio frequency power amplifiers with actively damped filter

Audio frequency power amplifiers with actively damped filter

High dynamic class-D power amplifier

Class-D amplifiers have high efficiency and are used when high audio frequency power is necessary and also when low power consumption in battery powered equipment is required. A new kind of class-D amplifier is presented and analyzed. The ripple of the high power class-D amplifier stage is compensated by a small (low power) high dynamic amplifier, which can be realized either as an analog one or as a second power class-D converter. The main part of the power is handled by a half-bridge with relatively small switching frequency (compared to the output bandwidth) and therefore low switching losses. Furthermore, the compensation mechanism leads to no additional current or voltage stress in the main switching stage. In the presented example the switching frequency of the main power processor is selected at only twice the required output bandwidth of the amplifier. The resulting output ripple is compensated by using the transformer coupled supplement power processor. Only small filters are necessary. The concept is well suited for consumer as well as aerospace applications as due to the improved efficiency, and the battery lifetime can be increased without any quality reduction.

Audio frequency power amplifiers with actively damped filter

An inverter for an audio amplifier. The inverter comprises a current damping feedback loop for actively damping oscillations caused by an output inductor within the inverter. A forward compensator is provided to compensate for the frequency response of the actively damped filter. The resulting inverter generates an output voltage that tracks an input voltage thereof with improved frequency response within the frequency range of interest.

High-accuracy sampling wattmeter

A high-accuracy sampling wattmeter was developed to investigate the feasibility of using waveform sampling techniques for making very accurate power measurements at frequencies from 50 Hz to 1000 Hz. The goal of this study was to develop an instrument having measurement uncertainty of less than +or-50 p.p.m. over these frequencies. The wattmeter was built around a wideband instrument developed earlier, and it uses 16-b analog-to-digital (A/D) converters and includes a two-stage current transformer in one of the input modules. It operates with asynchronous sampling, and high accuracy is achieved by approximately synchronizing the interval over which sampls are taken with the period of the input signal. Special care was taken to design input stages with a flat frequency response and low temperature sensitivity. The wattmeter has been calibrated using an audio-frequency power bridge. The two instruments agreed to better than +or-50 p.p.m. of full scale over the 50 Hz to 1000 Hz frequency range at all power factors.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An international comparison of low audio frequency power meter calibrations conducted in 1989

Summary form only given. The results of comparison of audio-frequency power meter calibrations conducted in 1989 between the National Research Council, Canada, the National Physical Laboratory, United Kingdom, and the National Institute of Standards and Technology, USA, are reported. A time-division watt converter, developed at the National Research Council, was used as the transfer standard. The measurements were made at 120 V, 5 A, power factors of one, zero lead and lag, and frequencies up to 5 kHz. >

Performance evaluation of a new audio-frequency power bridge

Several techniques for measuring active and reactive power in the 50-Hz to 20-kHz frequency range are described. These approaches were developed to evaluate a new high-accuracy, audio-frequency power bridge that is based on AC voltage and impedance measurements. The results indicate that its uncertainties are within the expected +or-200 p.p.m. for active power. The bridge and a high-precision sampling wattmeter constructed using two sampling digital voltmeters are described. A dual-channel digitally synthesized source was used to verify measurements at zero power factor. >

Audio frequency power amplifier with improved circuit topology

The present invention is an audio frequency power amplifier input circuit having improved vacuum tube circuit topology. The improved circuit includes a direct current feedback circuit within the input circuitry which stabilizes the operating point of a phase inverter. The feedback circuit maintains optimum operation of the circuit despite variations in tube characteristics or supply voltages. Another aspect of the improved circuit comprises a low impedance phase inverter which improves the drive capability of the phase inverter to push-pull power output vacuum-tube grids.

A device for audio-frequency power measurement

A device for the measurement of audio-frequency power, voltage and current is discussed. The full range of power factors are accommodated (cos phi =0 to 1). Voltage and current measuring ranges are 15-600 V and 0.1-10 A, respectively. When cos phi =1, the permissible error of the power measurement is from 50 to 150 p.p.m. over the frequency range of 40 Hz to 10 kHz (including the line power frequency). >

The New Zealand harmonic legislation

The New Zealand power system, with a number of large rectifier loads and extensive use of audiofrequency power system signalling (ripple control) for load management, presents particular problems to the designers of harmonic-control measures. The approach adopted in the Limitation of Harmonic Levels Notice differs from that adopted in other standards and guidelines in a number of areas, in particular in its adoption of individual current and voltage limits for the transmission system, the use of psophometrically weighted limits for both current and voltage, the provision of a detailed measurement schedule, and the approach to the equitable sharing of available harmonic capacity. In parallel with the standard, a specially designed monitoring system has been developed to gather information on system harmonic behaviour, and to present this information to a user. A primary role of this equipment will be in the monitoring of power system harmonic conditions, to assess the influence of the legislation in controlling harmonic levels.

High-frequency high-power static induction transistor

The principal operating mechanism of the static induction transistor (SIT) that shows exponential rather than the saturated I-V characteristics, is based on the static induction of both gate and drain voltages. It is known that the SIT has low noise, low distortion, and high audio-frequency power capability. The SIT is also a very promising device for high-frequency and high-power operation because of its short channel length, low gate series resistance, small gate-source capacitance, and small thermal resistance. Si SIT's which generate a 40-W output power at 200 MHz and 10 W at 1 GHz, with a cutoff frequency higher than 2.5 GHz, have been fabricated. This is the first step toward the realization of a power microwave SIT. Future developments of a higher power higher frequency SIT can be realized by employing a distributed electrode structure and traveling-wave operation.

Audio-frequency power amplifier

FIELD: electronic engineering. SUBSTANCE: amplifier has input stage 1 built around operational amplifier 2 with negative feedback circuit common for ac and DC currents in the form of voltage divider. Operational amplifier 2 is supplied with power through parametric regulators built around transistors 3 and 4. Voltage amplifying stage 22 uses balanced circuit arrangement with two transistors 23 and 24 connected into common-base circuit and is provided with circuit setting potential across these transistors which has two groups of parallel-connected diodes 26,27 and 28,29 integrated by resistor 30. Current amplifying unit 31 uses balanced circuit arrangement and has stages built around transistors 32-37 connected into common- collector circuit. Output stage of unit 31 has two series- connected resistors 38 and 39 connected to respective transistors 36 and 37. Unit 31 is also provided with temperature controller 43 using transistors 44 and 45 of different structure; power amplifier has negative feedback circuit common for DC and ac currents. EFFECT: reduced nonlinear distortions and improved reliability. 1 dwg:

Alternating-Current Loss Measurements in Thin-Film Type II Superconductors

An electrical technique is described for measuring the audio frequency power dissipation in superconducting thin films as a function of the ac current density, frequency, and applied dc magnetic field. This system has been used to study the ac losses in thin films of Nb and NbN, and also the ac and dc critical current densities in these materials. The results can be explained by assuming that both hysteresis and eddy current losses contribute.

Ionization gauge power supply for use in a pulsed magnetic field

An audio-frequency power supply for the filament of an ionization gauge is described. The frequency chosen is higher than the natural frequency of oscillation of the filament, hence the gauge may be used in a magnetic field. Stabilization is achieved by comparing the potential at one end of a high-stability resistance through which the emission current is flowing with a reference potential, and controlling the filament current from the difference of the two. Stability over several weeks of continuous working and over a pressure range of 10-3 to 10-6 mm Hg is better than 1%.

Design principles for junction transistor audio power amplifiers

Junction transistors may be employed as audio frequency power amplifiers which will supply up to several watts of output power. The fact that there are two basic types of transistor (n-p-n and p-n-p) allows a freedom of circuit design which is impossible with electron tubes. In power amplifier design the usual small signal assumptions cannot always be considered valid. Hence, large signal techniques must be applied in order to describe the behavior of the device. The non-linear distortion associated with large signal operation is discussed in terms of the transistor characteristics and methods of reducing this distortion are outlined. Operation in several circuit connections is considered with particular emphasis on the common emitter configuration.

Discussion on “The design of semi-conductor wattmeters for power-frequency and audio-frequency applications”, by Professor Barlow, and “Audio-frequency power measurements by dynamometer wattmeters”, by Dr. Arnold, before the Measurements Section, 23rd November, 1954

Discussion on “The design of semi-conductor wattmeters for power-frequency and audio-frequency applications”, by Professor Barlow, and “Audio-frequency power measurements by dynamometer wattmeters”, by Dr. Arnold, before the Measurements Section, 23rd November, 1954

Audio-frequency power measurements by dynamometer wattmeters

Dynamometer wattmeters can be designed and constructed for the measurement of power at frequencies up to about 20kc/s. The achievement of an accuracy at the higher audio frequencies comparable to that which is possible at power frequencies is dependent first upon certain precautions being taken with regard to the screening of the load and the wattmeter, and secondly upon the possibility of an accurate determination of the frequency-dependent errors of the wattmeter. The screening necessary is described, and an account is given of the methods adopted at the N.P.L. to calibrate wattmeters. For any dynamometer a frequency is eventually reached at which a significant instrument deflection is obtained with voltage only or current only applied to the terminals. This is considered to be the useful upper limit of frequency for that instrument.

The authors' replies to the discussion on “The design of semi-conductor wattmeters for power-frequency and audio-frequency applications” and “Audio-frequency power measurements by dynamometer wattmeters”

The authors' replies to the discussion on “The design of semi-conductor wattmeters for power-frequency and audio-frequency applications” and “Audio-frequency power measurements by dynamometer wattmeters”

A high efficiency - high quality audio frequency power amplifier

The development of the power amplifier discussed in this paper was undertaken with the objective of providing a large amount of good quality audio power in a small package at relatively low cost. The size of an amplifier package and its cost are dependent largely on the efficiency of operation and the power sensitivity of the output stage. Ream power tubes satisfy these two requirements more readily than triodes. The quality of the audio power is improved. by the use of push-pull operation and large amounts of feedback. The use of a suitable amount and type of feedback with beam power tubes eliminates the advantage of inherent low output impedance obtained with triodes. In Class A or Class AB operation the dynamic characteristics of the two tubes may be matched to obtain a reasonably linear characteristic, and while feedback is desirable its use may sometimes be avoided. In Class B operation it is not possible to match dynamic characteristics to get linear operation, and therefore a large